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JUST THE FACTSH

UMAN

BODY

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INFORMATION AT YOUR FINGERTIPSINFORMATION AT YOUR FINGERTIPSINFORMATION AT YOUR FINGERTIPS INFORMATION AT YOUR FINGERTIPS

INFORMATION AT YOUR FINGERTIPSINFORMATION AT YOUR FINGERTIPS INFORMATION AT YOUR FINGERTIPS

HUMANBODY

2

This edition published in the United States in 2006 by School Specialty Publishing, a member of the School Specialty Family.

Copyright © ticktock Entertainment Ltd 2005 First published in Great Britain in 2005 by ticktock Media Ltd. Printed in China.

All rights reserved. No part of this book may be reproduced, stored in a central retrieval system, or transmitted in any form or by

any means, electronic, mechanical, photocopying, recording, or otherwise, withouth the prior written permission of the publisher.

Written by Steve Parker.

Library of Congress-in-Publication Data is on file with the publisher.

Send all inquiries to:

School Specialty Publishing

8720 Orion Place

Columbus, OH 43240-2111

ISBN 0-7696- 4255-1

1 2 3 4 5 6 7 8 9 10 TTM 11 10 09 08 07 06

32

CONTENTS

This edition published in the United States in 2006 by School Specialty Publishing, a member of the School Specialty Family.

Copyright © ticktock Entertainment Ltd 2005 First published in Great Britain in 2005 by ticktock Media Ltd. Printed in China.

All rights reserved. No part of this book may be reproduced, stored in a central retrieval system, or transmitted in any form or by

any means, electronic, mechanical, photocopying, recording, or otherwise, withouth the prior written permission of the publisher.

Written by Steve Parker.

Library of Congress-in-Publication Data is on file with the publisher.

Send all inquiries to:

School Specialty Publishing

8720 Orion Place

Columbus, OH 43240-2111

ISBN 0-7696- 4255-1

1 2 3 4 5 6 7 8 9 10 TTM 11 10 09 08 07 06

HOW TO USE THIS BOOK....................................................................................4

BODY SYSTEMS................................................................................................................6• Integumentary • Muscular • Skeletal • Nervous • Sensory • Respiratory • Circulatory • Digestive • Urinary • Reproductive • Hormonal • Lymphatic • Immune

THE SKIN ..................................................................................................................................8• Sense of touch • Fingertips • Sweat • Layers of the skin • Microsensors • Shed skin • Skin thickness • Main tasks of the skin • Size of the skin

HAIR AND NAILS ....................................................................................10• Nail parts • Growth of nails • Hair thickness • Structure of a hair • Eyebrows • Eyelashes • Growth of hair • Hair life cycle • Why have hair? • Why have nails?

MUSCLES & MOVEMENT...................................................................................12• Types of muscle • Muscle used for facial expressions • Inside a muscle • Power of muscles • How muscles work • Muscle records

THE SKELETON...............................................................................................................14

• Size and variation • The coccyx • Cartilage • Bone strength• Tasks of the skeleton • Number of bones

BONES AND JOINTS ...............................................................................................16• Parts of a bone • What a bone contains • Bone records • Ligaments • Synovial fluid • The knee joint • Different types of joint • Head movements

THE NERVOUS SYSTEM ......................................................................................18• Parts of the nervous system • Nerve cells • Nerve signals • Spinal cord • Nerve lengths

THE BRAIN..........................................................................................................................20• The cortex • Energy requirements • Blood supply to the brain • Brain parts • Size of the brain • Sleep • Left and right • Brain development through life

EYES AND SIGHT ........................................................................................................22• Parts of the eye • How the eye sees • Cones • Blind spot • Moving the eye • Blinking

EARS AND HEARING..............................................................................................24• How we hear • Sections of the ear • Bones in the ear • Pitch• Sense of balance • Stereo hearing • Ear measurements • The loudness of sounds

NOSE AND TONGUE................................................................................................26• How we smell • Parts of the nose • Parts of the tongue• How we taste • Other tasks of the tongue

TEETH AND JAW ..........................................................................................................28• Numbers of teeth • Parts of a tooth • Plaque • When teeth grow• Chewing • Roof of the mouth • Saliva

LUNGS AND BREATHING ..................................................................................30• Size and shape of the lungs • Gases used • Breathing rates• Parts of the lungs • The voicebox • Speech

THE HEART .........................................................................................................................32• Parts of the heart • Heart’s blood supply • Heart’s job • The pulse• Changing pulse rate through life • How the heart works • Size and shape • Typical day

CIRCULATORY SYSTEM .......................................................................................34• Veins and arteries • Using oxygen • Types of blood vessels• Size and length of blood vessels • Journey times of blood• Blood pressure in blood vessels

BLOOD .....................................................................................................................................36

• Blood flow • Amount of blood in the body • Blood types• Red blood cells • What is in blood?

DIGESTION..........................................................................................................................38• The digestive tract • Digestive juices • Length of food’s journey • Faeces • Stomach • Appendix • Small intestine • Large intestine

FOOD AND NUTRIENTS ......................................................................................40

• Food groups • Daily needs • Carbohydrates • Fats and oils • Proteins • Fiber • Fruit and vegetables • Vitamins • Minerals

LIVER AND PANCREAS........................................................................................42• Tasks of the liver • Gall bladder • Bile • Blood supply to the liver• Liver of young children • Jaundice • Shape of the liver• Shape of the pancreas

KIDNEYS AND URINARY SYSTEM .........................................................44• Size and shape of kidneys • Parts of the kidney • Nephrons • Urinary parts • Size of the bladder • Male and female systems• Filtering the blood

GENES.......................................................................................................................................46• DNA • Chromosomes • Genes • Inherited characteristics • Genetic fingerprinting • Clones

REPRODUCTION..................................................................48• Size and shape of female reproductive parts• Female parts • Egg release cycle• Eggs and sperm • Male parts • Size and shape of male reproductive parts

STAGES OF LIFE.....................................................50

• Growth rates • How an egg is fertilized • Embryo • Fetus • New baby • Puberty • Aging

HORMONES ............................................................52• Thyroid • Parathyroid • Pituitary • Pancreas • Thymus • Adrenals • Adrenaline• Other hormone making parts

LYMPH AND IMMUNE SYSTEMS ................................................................54• Lymph nodes • Lymph fluid • Lymphocytes• How the immune system works• Types of immunity

DISEASES AND MEDICINES.......................56• Types of medicines • Medical drugs • Causes of illness and disease • Bacteria • Viruses • Protists • Microfungi • Medical specialists

GLOSSARY ....................................................................58

INDEX .................................................................................60

4

42

Your body can’t digest food with just its digestive tract (passageway) –mouth, gullet, stomach and intestines. Also needed are two partscalled the liver and pancreas. These are next to the stomach and

they are digestive glands, which means they make powerful substances to break down food in the intestines. Together with the digestive tract,the liver and pancreas make up the whole digestive system.

The gall bladder is a small storage bag underthe liver.

• It is 8 cm long and 3 cm wide.

• Some of the bile fluid made inthe liver is stored in the gallbladder.

• The gall bladder can hold up to 50 millilitres of bile.

• After a meal, bile pours fromthe liver along the main bileduct (tube), and from the gallbladder along the cystic duct,into the small intestine.

• Bile helps to break apart or digest the fats and oils in foods.

• The liver makes up to one litre of bile each day.

The liver has more than 500known tasks in the body –and probably more thathaven’t yet been discovered.Some of the main ones are:

• Breaking down nutrients and other substances from digestion,brought direct to the liver from the small intestine.

• Storing vitamins for times whenthey may be lacking in food.

• Making bile, a digestive juice.

• Breaking apart old, dead, worn-out red blood cells.

• Breaking down toxins orpossibly harmful substances,like alcohol and poisons.

• Helping to control the amount ofwater in blood and body tissues.

• If levels of blood sugar(glucose) are too high,hormones from the pancreas tellthe liver to change the glucoseinto glycogen and store it.

• If levels of blood sugar(glucose) are too low,hormones from the pancreas tellthe liver to release the glycogenit has stored.

THE LIVER’S TASKS

The liver is so busy withchemical processes and tasksthat it makes lots of heat.

• When the body is at rest and themuscles are still, the liver makes

up to one-fifth of the body’s totalwarmth.

• The heat from the liver isn’twasted. The blood spreads out theheat all around the body.

WARM LIVER

See pages 34-35 for information on the circulatory system.

LIVER & PANCREAS

The liver is in the upper abdomen, behind

the lower right ribs. The pancreas is in the upper left abdomen, behind the stomach.

WHERE IN THE BODY?

WHEN THINGSGO WRONG

Alcohol is a toxin which the liver breaks down andmakes harmless. Too much

alcohol can overload the liverand cause a serious disease

called cirrhosis.

GALL BLADDERAND BILE

liver

pancreas

gall bladder

HOW TO USE THIS BOOK

JUST THE FACTS, HUMAN BODY is a quick and easy-to-use way to look up facts about the

systems that control how our bodies work. Every page is packed with cut-away diagrams, charts,

scientific terms and key pieces of information. For fast access to just the facts, follow the tips on

these pages.

TWO QUICK WAYSTO FIND A FACT:

Look at the detailed CONTENTS list onpage 3 to find your

topic of interest.

Turn to the relevantpage and use the BOX HEADINGS to find theinformation box you need.

Turn to the INDEX that starts on page 60 and search for key words relating to your research.

• The index will direct you to the correct page, and where on the page to find the fact you need.

1

2

JUST THE FACTSEach topic box presents the facts youneed in short, quick-to-read bullet points.

WHERE IN THE BODY?An at-a-glance look at where thepart of the body can be found.

PICTURE CAPTIONSCaptions explain whatis in the pictures.

EXTRA INFORMATIONThe black box on the right handside of the page explains a newaspect of the main topic.

6–7 Body Systems 58–59 Glossary

LINKSLook for the purple links throughout thebook. Each link gives details of otherpages where related or additional factscan be found.

3

HOW TO USE THIS BOOK ............................................................................4–5

BODY SYSTEMS ........................................................................................................6–7• Integumentary • Skeletal • Muscular • Nervous • Sensory Respiratory • Circulatory • Digestive • Urinary • ReproductiveHormonal • Lymphatic • Immune

THE SKIN...........................................................................................................................8–9• Sense of touch • Fingertips • Sweat • Layers of the skin • Microsensors • Shed skin • Skin thickness • Main tasks of the skin • Size of the skin

HAIR AND NAILS ...........................................................................10–11• Nail parts • Growth of nails • Hair thickness • Structure of a hair • Eyebrows • Eyelashes • Growth of hair • Hair life cycle • Why have hair? • Why have nails?

MUSCLES & MOVEMENT ........................................................................12-13• Types of muscle • Muscle used for facial expressions • Inside a muscle • Power of muscles • How muscles work • Muscle records

THE SKELETON.....................................................................................................14-15• Size and variation • The coccyx • Cartilage • Bone strength• Tasks of the skeleton • Number of bones

BONES AND JOINTS .....................................................................................16-17• Parts of a bone • What a bone contains • Bone records • Ligaments • Synovial fluid • The knee joint • Different types of joint • Head movements

THE NERVOUS SYSTEM............................................................................18-19• Parts of the nervous system • Nerve cells • Nerve signals • Spinal cord • Nerve lengths

THE BRAIN ...............................................................................................................20-21• The cortex • Energy requirements • Blood supply to the brain • Brain parts • Size of the brain • Sleep • Left and right • Brain development through life

EYES AND SIGHT..............................................................................................22-23• Parts of the eye • How the eye sees • Cones • Blind spot • Moving the eye • Blinking

EARS & HEARING............................................................................................24-25• How we hear • Sections of the ear • Bones in the ear • Pitch• Sense of balance • Stereo hearing • Ear measurements • The loudness of sounds

NOSE & TONGUE..............................................................................................26-27• How we smell • Parts of the nose • Parts of the tongue• How we taste • Other tasks of the tongue

TEETH & JAW ........................................................................................................28-29• Numbers of teeth • Parts of a tooth • Plaque • When teeth grow• Chewing • Roof of the mouth • Saliva

LUNGS & BREATHING...............................................................................30–31• Size and shape of the lungs • Gases used • Breathing rates• Parts of the lungs • The voicebox • Speech

THE HEART..............................................................................................................32–33• Parts of the heart • Heart’s blood supply • Heart’s job • The pulse• Changing pulse rate through life • How the heart works • Size and shape • Typical day

CIRCULATORY SYSTEM.............................................................................34-35• Veins and arteries • Using oxygen • Types of blood vessels• Size and length of blood vessels • Journey times of blood• Blood pressure in blood vessels

BLOOD...........................................................................................................................36-37• Blood flow • Amount of blood in the body • Blood groups• Red blood cells • What is in blood?

DIGESTION...............................................................................................................38-39• The digestive tract • Digestive juices • Length of food’s journey • Faeces • Stomach • Appendix • Small intestine • Large intestine

FOOD & NUTRIENTS ....................................................................................40-41• Food groups • Daily needs • Carbohydrates • Fats and oils • Proteins • Fibre • Fruit and vegetables • Vitamins • Minerals

LIVER AND PANCREAS..............................................................................42-43• Tasks of the liver • Gall bladder • Bile • Blood supply to the liver• Liver of young children • Jaundice • Shape of the liver• Shape of the pancreas

KIDNEYS & URINARY SYSTEM .......................................................44-45• Size and shape of kidneys • Parts of the kidney • Nephrons • Urinary parts • Size of the bladder • Male and female systems• Filtering the blood

GENETICS ...................................................................................................................46-47• DNA • Chromosomes • Genes • Inherited characteristics • Genetic fingerprinting • Clones

REPRODUCTION .......................................................48-49• Size and shape of female reproductive parts• Female parts • Egg release cycle• Eggs and sperm • Male parts • Size and shape of male reproductive parts

STAGES OF LIFE...........................................50-51

• Growth rates • How an egg is fertilized • Embryo • Fetus • New baby • Puberty • Ageing

HORMONES..................................................52-53• Thyroid • Parathyroid • Pituitary • Pancreas • Thymus • Adrenals • Adrenaline• Other hormone making parts

LYMPH & IMMUNE SYSTEMS......................................................54-55• Lymph nodes • Lymph fluid • Lymphocytes• How the immune system works• Types of immunity

DISEASES & MEDICINES ...................56–57• Types of medicines • Medical drugs • Causes of illness and disease • Bacteria • Viruses • Protists • Micro-fungi • Medical specialists

GLOSSARY..........................................................58-59

INDEX......................................................................60–64

CONTENTS

• The digestive tract • Digestive juices • Length of food’s journey • Faeces • Stomach • Appendix • Small intestine • Large intestine






60

Aabdomen 43b-caccidents 56c-dAchilles (calcaneal) tendon

13dacids 39a-cacquired immunity 55dactin 13a-cactive immunity 55d

‘Adam’s apple’ 31dadenine 46aadenoids (pharyngeal

tonsils) 54a, 54c-dadrenal glands 53c, 53dadrenaline (epinephrine)

36b, 52b-d, 53c, 53dageing 51dalcohol 21d, 42a-caldosterone 53calleles 47a-callergies 56b, 56c-dalveoli 31a-camino acids 41aammonia 44a-damniotic fluid 50a-danaesthetics 56a, 57danaesthetist 57danalgesics 56aankles 15danti-emetics 56banti-inflammatories 56bantibiotic drugs 56b, 57aantibodies 37d, 54b,

55a-c, 55danticoagluants 56banticonvulsants 56bantidepressants 56bantidiuretic hormone (ADH)

52c-dantifungal 56bantigens 55a-c, 55dantihistamine 56bantipyretic 56bantiseptic 56bantitoxin 56bantiviral 56banus 6-7c, 38a, 39a-c

anvil bone (incus) 24aaorta 33d, 34a-b,

34c-daortic valve 33a-c,

33dappendix 38a,

39daqueous humour

23a-carms 15d

arteries 20a, 33a-c,34, 35, 36a, 43b-c,

44b-darterioles 35a-c, 35d,

36bartificial acquired immunity 55d

ascorbic acid (Vitamin

C) 40b, 41dasthma 56bastigmatism 23catlas vertebra 16c-datria, heart 33a-c, 33datriopeptin 53a-cauditory nerve 25a-cauricle (pinna) 24aauricularis muscle 12a-dautoimmune problems

56c-dautonomic nerve system

18baxillary hair 10b-daxis 16c-daxons 18c-d, 19a-b, 19c,

20b-c

Bbabies 14b-c, 15a-b, 50-1bacilli 57abackbone 15dbacteria 6-7c, 45a-c, 55a-

b, 55c, 56b, 57abacterial infections 57abalance 6-7c, 24a-dball-and-socket joint 17dbeta-blocker 56abile 42a-c, 42d, 43abladder 44b-d, 45a-cblastocyst 50b-dblinking 23cblood 15a-c, 16a, 34b-d,

36-7, 40a, 45dclotting 6-7b, 36c-d, 37d,

40a, 56a, 56bblood groups 36c-dblood pressure 21a-c, 35a-

c, 40c-d, 53a-c, 56ablood sugar (glucose) 12a,

20a, 30b-d, 37d, 40c-d,42a-c, 53

blood transfusions 36c-dblood vessels 34a, 34b-d,

36b-d, 53d, 56abody salts 37d, 53a-cbody systems 6-7

see also named systemsbone marrow 15a-c, 16a,

37a-cbones 6-7a, 16-17, 40a,

41asee also named bones

bowel motions 6-7c, 39b-cBowman’s capsule 44a-dbrain 6-7a, 18a, 18b-d,

20-1, 24c-d, 37a-b,52b-d

breastbone 15dbreathing 21a-c, 30-1,

40c-d, 53dbronchi 31a-cbronchioles 31a-c, 56abronchodilator 56abuccinator muscle 12a-d

Ccaecum 39dcalcaneal (Achilles) tendon

13dcalciferol (Vitamin D) 9d,

41dcalcitonin 52acalcium 15a-c, 16b-d, 40a,

40b, 41c, 52a, 52bcalcium carbonate 16b-dcalcium phosphate 16b-dcancers 56c-dcapillaries 35a-c, 35d,

36acarbohydrates 40, 43acarbon dioxide 6-7a,

31a-c, 37dcarbonate 16b-dcardiac muscle

(myocardium) 12b-d,32c-d, 33a-c

cardiologist 57dcardiovascular system

6-7b, 34-5carotene (Vitamin A) 41dcarotid artery 20acartilage 15a-b, 17a-c,

17dcells 6-7a, 40, 49a-c,

50b-dsee also named types ofcell

cellulose 40b-dcerebellum 21a-ccerebral cortex 20b-c,

21a-ccerebral vessels 35a-ccerebrospinal fluid (CSF)

19a-b, 21a-bcerebrum 21a-ccervical vertebrae 15d,

16c-dcervix 48b, 48c-dchemosenses 26b-dchemotherapy 56achewing 29dchloride 40b

The letters a, b, c, d, followingthe page number indicate thecolumn (lettering from left toright) in which the informationmay be found on that page.

INDEX





36b, 52b-d, 53c, 53dageing 51dalcohol 21d, 42a-caldosterone 53calleles 47a-callergies 56b, 56c-dalveoli 31a-camino acids 41aammonia 44a-damniotic fluid 50a-danaesthetics 56a, 57danaesthetist 57d

aaaaaaaaa

a

axaxax


IND

INTRODUCTION TO TOPIC

BOX HEADINGSLook for heading words linked to yourresearch to guide you to the right fact box.

CUTAWAY DIAGRAMSClear, accurate diagrams show howthe parts of the body fit together.

54

4342

Your body can’t digest food with just its digestive tract (passageway) –mouth, gullet, stomach and intestines. Also needed are two partscalled the liver and pancreas. These are next to the stomach and

they are digestive glands, which means they make powerful substances to break down food in the intestines. Together with the digestive tract,the liver and pancreas make up the whole digestive system.

• Most body parts are supplied withblood flowing along one or a fewmain arteries.

• The liver has a main artery, thehepatic artery.

• The liver also has a second andmuch greater blood supply.

• This comes along a vessel calledthe hepatic portal vein.

• The hepatic portal vein is the only main vein that does not take blood straight back to the heart.

• It runs from the intestines to the liver, bringing blood full ofnutrients from digestion.

W H A T I S T H E L I V E R ?

The liver is the largestsingle part or organ insidethe body.

• Wedge-shaped, dark red incolour.

• Typical weight 1.5 kg.

• Depth at widest part on right side15 cm.

• Has a larger right lobe andsmaller left lobe.

• Lobes separated by a stronglayer, the falciform ligament.


• It is 8 cm long and 3 cm wide.


• The gall bladder can hold up to 50 millilitres of bile.

• After a meal, bile pours fromthe liver along the main bileduct (tube), and from the gallbladder along the cystic duct,into the small intestine.

• Bile helps to break apart or digest the fats and oils in foods.

• The liver makes up to one litre of bile each day.

The liver has more than 500known tasks in the body –and probably more thathaven’t yet been discovered.Some of the main ones are:

• Breaking down nutrients and other substances from digestion,brought direct to the liver from the small intestine.




• Breaking down toxins orpossibly harmful substances,like alcohol and poisons.

• Helping to control the amount ofwater in blood and body tissues.

• If levels of blood sugar(glucose) are too high,hormones from the pancreas tellthe liver to change the glucoseinto glycogen and store it.

• If levels of blood sugar(glucose) are too low,hormones from the pancreas tellthe liver to release the glycogenit has stored.

THE LIVER’S TASKS

Most babies and youngchildren have bigtummies (abdomens).This is partly becausetheir liver is much larger,in proportion to thebody’s overall size, thanthe liver of an adult.

• An adult liver is usually 1⁄40thof total body weight.

• A baby’s liver is nearer 1⁄20thof total body weight.

• Pancreas has two main jobs.

• One is to make hormones.

• The other is to make digestivechemicals called pancreaticjuices.

• These juices contain about 15powerful enzymes that breakapart many substances infoods, including proteins,carbohydrates and fats.

• Pancreas makes about 1.5litres of digestive juices daily.

• During a meal these passalong the pancreatic duct tubesinto the small intestine, toattack and digest foods there.

HOW THEPANCREAS WORKS




• The heat from the liver isn’twasted. The blood spreads out theheat all around the body.

Fatty foods, such as chips, are broken apart by enzymes

made in the pancreas.

WARM LIVER

See pages 34-35 for information on the circulatory system.

LIVER & PANCREAS



WHERE IN THE BODY?

W H A T I S T H EPANCREAS?

The pancreas is a long,slim, wedge- or triangular-shaped part.

• It is soft, greyish-pink in colour.• Typical weight 0.1 kg.

• Typical length 15 cm.

• Has three main parts: head(wide end), body (middle) andtail (tapering end).

• See pages 36-37 forinformation on the blood.

By the time a babybecomes a toddler, theirliver isn’t such a largeproportion of their totalbody weight.

• See page 52 forinformation on hormones.

One of the liver’s main functions is to break down nutrients forthe body. This means the liver has a unique blood supply.

A yellowish tinge to the skin and eyes is known asjaundice, and it is often a signof liver trouble.

Usually the liver breaks down old red blood cells and gets rid of thecolouring substance in bile fluid. If something goes wrong the colouringsubstance builds up in blood and skinand causes jaundice.Hepatitis, an infection of the liver, cancause jaundice.

WHEN THINGSGO WRONG

Alcohol is a toxin which the liver breaks down andmakes harmless. Too much

alcohol can overload the liverand cause a serious disease

called cirrhosis.


BABY LIVER

UNUSUAL SUPPLY

liver

liver

pancreas

liver

pancreas

gall bladder

• Mouth, teeth, throat, gullet, stomach, intestines, rectum and anus make up the digestive passagewayor tract.

• Liver, gall bladder and pancreas plus the tract make up the whole digestive system.• Breaks down or digests food into nutrients tiny enough

to take into the body.• Gets rid of leftovers as solid wastes (bowel motions, faeces).• Nutrients provide energy for all life processes and raw

materialsfor growth, maintenance and repairing everyday wear-

and-tear.

DIGESTIVE SYSTEM

• About 640 skeletal muscles all overthe body, mostly attached tobones (skeletal or voluntary

muscle).• Muscle layers in the walls

of inner parts like thestomach and intestines

(visceral orinvoluntary muscle).

• Muscle in the walls of the heart(heart muscle or myocardium).

• Muscles get shorter or contract to produce all forms of bodily

movement.• Sometimes combined with bones

and joints as the musculoskeletalsystem.

• Nose, windpipe, main chest airways and lungs.

• Obtains essential oxygen from the air around,and passes it to the blood for distribution.

• Gets rid of waste carbondioxide, which would be

poisonous if it built up in the blood.

• Useful ‘extrafunction’ is theability to make

vocal sounds and speech.

• Heart, blood vessels and blood.• Heart provides pumping power to send blood all around

the body.• Blood spreads vital oxygen, nutrients, hormones and

many other substances to all body parts.• Blood collects wastes and unwanted

substances from all body parts.• Blood clots to seal wounds

and cuts.• Closely involved with the

immune system in self-defence and fightingdisease.

CIRCULATORY (CARDIOVASCULAR) SYSTEM

• Lymph vessels, lymph nodes (‘glands’), lymphducts and lymph fluid.

• Gathers general body fluids from between cells and tissues.

• One-way flow channels fluid through lymphnetwork of nodes and vessels.

• Helps to distribute nutrients and collect wastes.

• Lymph fluid empties into blood system.• Closely linked with immune system.

• Defends the body against invadingdangers such as bacteria, virusesand other microbes.

• Gets rid of debris in tissues fromnormal wear-and-tear.

• Helps recovery from disease and illness.

• Helps repair of injury and normal wear-and-tear.• Keeps watch for problems and disease processes arising

inside the body, such as malignant (cancerous) cells.

• Only system which differs significantly in females and males.• Only system which is not working at birth, but starts to function

at puberty.• Male system produces sperm cells continually, millions per day.• Female system produces ripe egg cells, about one every 28 days, during menstrual cycle.

• If egg cell joins sperm cell to form an embryo, female systemnourishes this as it grows into a baby inside the womb.

The body is often divided into body systems, each one of which performs a certain job. Body systems are made from microscopic

‘building blocks’ called cells. A typical cell is only0.03 mm across, and there are about 50 million

million cells in the body. There are many differentkinds of cells, like nerve cells, muscle cells and so on. Many

cells of the same kind form a tissue, such as nerve tissue or fat tissue.Different kinds of tissue make up a main part of the body, known asan organ, like the brain, stomach or kidney. Severalorgans working together to carry out one majortask or function, like digesting food, are knownas a body system. About a dozen major systemsmake up the whole human body.

• Eyes, ears, nose, tongue and skinmake up the five main sets ofsense organs.• Also sensors inside the body fortemperature, blood pressure,

oxygen levels, positions of joints, amount of stretch in muscles and many other changes.

• Gravity and motion sensors in the inner earcontribute to the process of balance.

• Sometimes included as part of the nervoussystem, since the main sense organs are ineffect the specialized endings of sensorynerves.

• Kidneys, ureters, bladder and urethra.• Filters blood to get rid of unwanted substances and wastes.• Forms unwanted substances and wastes into

liquid waste or urine.• Stores urine, then releases it to

the outside.• Controls amount and concentration

of blood and body fluids, ‘waterbalance’, by adjusting amount of water lost in urine.

• About 10 main parts called endocrine or hormone-making glands.

• Some organs with other main tasks, like thestomach and heart, also make hormones.

• Hormones spread around the body in blood.• Closely linked to nervous system for coordinated

control of inner body processes.• Closely linked with reproductive system and

controls it by sex hormones.

• Skin, hair and nails.• Protect softinner parts fromphysical wear

and knocks, dirt,water, sun’s rays and

other harm.• Skin keeps in essential body fluids,

salts and minerals.• Helps to control body temperature

by sweating and flushing to loseheat, or going pale with‘goosebumps’ to retain heat.

• Provides sense of touch (seeSensory system).

• Gets rid of small amounts of wastesubstances, in sweat.

• Brain, spinal cord and peripheral nerves.• Controls and coordinates all body processes, from breathing and heartbeat to

making movements.• Allows mental processes such as thoughts, recalling memoriesand making decisions.• Sensory nerves bring information from the sense organs and other sensors.

• Motor nerves carry instructions to muscles about movement, and to glands about releasing their products.

• Works along with the hormonal system.

• 208 bones and the variouskinds of joints between them.• Gives physical support to holdup the body’s soft, floppy parts.

• Gives protection to certainbody parts like the brain,

eyes, heart, lungs.• Pulled by muscles, to allow movement.

• Acts as a store or reservoirof valuable minerals like calcium, in case these are in short supply in food.

• Sometimes combined withmuscles as the

musculoskeletal system.

RESPIRATORY SYSTEMBODY SYSTEMS INTEGUMENTARYSYSTEM

SENSORY SYSTEM

URINARY SYSTEM

LYMPHATIC SYSTEMNERVOUS SYSTEM

HORMONAL (ENDOCRINE) SYSTEM

IMMUNE SYSTEM

REPRODUCTIVE SYSTEM

MUSCULAR SYSTEM

6 7

SKELETAL SYSTEM

GLOSSARYmedulla of the kidney, or theadrenal medulla of theadrenal gland.

Meninges Three thin layerscovering the brain and spinalcord, and also making andcontaining cerebrospinalfluid. They are known as thedura mater, arachnoid andpia mater.

Meiosis Part of special typeof cell division, when thechromosomes are not copiedand only one set (not adouble-set) moves into each resulting cell.

Metabolism All of thebody’s thousands of chemicalprocesses, changes andreactions, such as breakingapart blood sugar to releaseenergy, and building upamino acids into proteins.

Mineral A simple chemicalsubstance, usually a metalsuch as iron or calcium, or a salt-type chemical such asphosphate, which the bodyneeds in small quantities infood to stay healthy.

Mitosis Part of normal cell division, when thechromosomes have beencopied and one full double-set moves into each resultingcell.

Motor nerve A nerve thatcarries messages from thebrain to a muscle, telling itwhen to contract, or to agland, telling it when torelease its content.

Mucus Thickish, sticky, slimysubstance made by manybody parts, often forprotection and lubrication,such as inside the nose andwithin the stomach.

Myo- To do with muscles,such as myocardium or heartmuscle.

Nephron Microscopicfiltering unit in the kidney forcleaning the blood.

Neuron A nerve cell, thebasic unit of the nervoussystem.

Olfactory To do with thenose and smell.

Optic To do with the eye,especially the optic nervecarrying messages from theeye to the brain.

Papillae Small lumps,bumps or ‘pimples’ on abody part such as thetongue.

Peripheral nerves Thebodywide network of nerves,excluding the central nervoussystem of brain and spinalcord.

Peristalsis Wave-likecontractions of muscles in thewall of a body tube, such asthe small intestine, ureter(from kidney to bladder) or oviduct (from ovary towomb).

Pulmonary To do with thelungs.

Renal To do with thekidneys.

Sebum Natural waxy-oilysubstance made in sebaceousglands associated with hairfollicles that keeps skinsupple and fairly waterproof.

Sensory nerve A nervethat carries messages to thebrain from a sense organ orpart, such as the eye, theear, the tiny stretch sensors inmuscles and joints, and theblood pressure sensors inmain arteries.

Skeletal To do with theskeleton, the 206 bones thatform the body’s supportinginner framework.

System In the body, aset of major parts ororgans that all worktogether to fulfil onemain task, such asthe respiratorysystem, which

transfers oxygen from the airaround to the blood.

Tendon The string, fibrous,rope-like end of a muscle,where it tapers and joins to abone.

Thoracic To do with thechest, which is also calledthe thorax.

Thrombosis The process ofblood going lumpy to form aclot, which is also known asa thrombus.

Tissue A group of verysimilar cells all doing the same job, such as muscletissue, adipose or fat tissue,epithelial (covering or lining)tissue, connective tissue(joining and filling in gapsbetween other parts).

Valve A flap, pocket orsimilar part which allows a substance to pass one way but not the other.

Vein A blood vessel (tube)which conveys blood towardsthe heart.

Vertebra A single bone ofthe row of bones called thebackbone, spine or vertebralcolumn.

Villi Tiny finger-like projectsfrom the microscopic cells invarious body parts, includingthe inner lining of the smallintestine.

Visceral To do with themain parts or organs insidethe abdomen (the lower partof the main body or torso),mainly the stomach andintestines, kidneys andbladder, and in females,reproductive parts.

Vitamin Substance neededin fairly small amounts infood for the body to workwell and stay healthy.

59

Abdomen The lower part of the main body or torso,below the chest, whichcontains mainly digestive andexcretory (waste-disposal)parts, and in females,reproductive parts.

Artery A blood vessel (tube)which conveys blood awayfrom the heart.

Axon The very long, thinpart of a nerve cell or neuron,also called a nerve fibre.

Bladder Bag-like sac orcontainer for storing fluids.The body has several,including the urinary bladder (often just called ‘thebladder’) and gall bladder.

Blood sugar Also calledglucose, the body’s mainenergy source, used by all its microscopic cells to carryout their life processes andfunctions.

Capillary The smallest typeof blood vessels, usually lessthan one millimetre long andtoo thin to see except througha microscope.

Cardiac To do with theheart.

Cartilage Tough, light,slightly bendy andcompressible bodysubstance, often called‘gristle’, which forms parts of the skeleton such as theears and nose, and alsocovers the ends of bones in joints.

Cell The basic microscopic‘building block’ of the body,a single living unit, with mostcells being 0.01-0.05 mmacross. The body containsover 50 million million cells.

Central nervous systemThe brain and spinal cord.

Cerebral To do with thecerebrum, the largest part of the brain which forms itswrinkled domed shape.

Cerebrospinal fluid Liquidsurrounding the brain andspinal cord, to protect andcushion them as well as helpprovide nourishment andtake away wastes.

Cilium Microscopic hair,usually sticking out fromthe surface of

a cell, which canwave or bend, andperhaps sensesubstances as in the

olfactory epithelium ofthe nose and in the tastebuds on the tongue. (Plural:cilia.)

Clone A living thing withexactly the same genes asanother living thing.

Collagen Tiny, tough, strongfibres found in body parts

such as skin and bones.

Cortex The outer part orlayer of a body part, such as the renal cortex of thekidney, or the cerebral cortex of the brain.

Cranium The upper domedpart of the skull or ‘braincase’, which covers andprotects the brain.

Cermis The inner layer ofskin, under the epidermis(see below), which containsthe touch sensors, hairfollicles and sweat glands.

DNA De-oxyribonucleicacid, the chemical substancethat forms the geneticinformation or genes.

Embryo The name for adeveloping human body,from fertilization as a single cell, to eight weekslater.

Endocrine To do withhormones and the hormonalsystem (see hormone).

Enzymes Substanceswhich alter the speed of achemical change or reaction,usually speeding it up, butwhich remain unchangedthemselves at the end of the reaction.

Epidermis The protectiveouter layer of skin, which isalways being worn away butcontinually replacing itself.

Excretory To do withremoving waste substancesfrom the body. The mainexcretory system is made up of the kidneys, bladder andtheir linking tubes.

Fertilization When an eggcell joins a sperm cell to startthe development of a newhuman body.

Fetus A developing humanbody from eight weeks afterfertilization until birth.

Fovea The small area in theretina of the eye where visionis most detailed and clearest,due to the great number ofcone cells.

Gastric To do with thestomach.

Gland A body part thatmakes a substance orproduct which it thenreleases, such as the tearglands which make tear fluidfor the eyes, and the sweatglands in the skin.

Glucose See blood sugar.

Gustatory To do with thetongue and taste.

Hepatic To do with the liver.

Hormone A natural‘chemical messengers’ thatcirculates in the blood andaffects how certain bodyparts work, helping thenervous system to control and coordinate all bodyprocesses.

Humour Old word used todescribe various body fluids,still used in some cases, forexample, to describe thefluids inside the eye, thevitreous (‘glassy’) humourand aqueous (‘watery’)humour.

Immunity Protection orresistance to microbial germs and other harmfulsubstances.

IntegumentaryConcerning the skin andother coverings, includingnails and hair.

Ligament A stretchy, strap-like part that joins the bonesaround a joint, so the bonesdo not move too far apart.

Medulla The inner orcentral region of a bodypart, such as the renal

GLOSSARY

58

HOW TO USE THIS BOOK

JUST THE FACTS, HUMAN BODY is a quick and easy-to-use way to look up facts about the

systems that control how our bodies work. Every page is packed with cut-away diagrams, charts,

scientific terms and key pieces of information. For fast access to just the facts, follow the tips on

these pages.

TWO QUICK WAYSTO FIND A FACT:

Look at the detailed CONTENTS list onpage 3 to find your

topic of interest.

Turn to the relevantpage and use the BOX HEADINGS to find theinformation box you need.

Turn to the INDEX that starts on page 60 and search for key words relating to your research.

• The index will direct you to the correct page, and where on the page to find the fact you need.

GLOSSARY• A GLOSSARY of words and terms

used in this book begins on page 58.• The glossary words provide

additional information to supplementthe facts on the main pages.

1

2

JUST THE FACTSEach topic box presents the facts youneed in short, quick-to-read bullet points.

WHERE IN THE BODY?An at-a-glance look at where thepart of the body can be found.

PICTURE CAPTIONSCaptions explain whatis in the pictures.

EXTRA INFORMATIONThe black box on the right handside of the page explains a newaspect of the main topic.

6–7 Body Systems 58–59 Glossary

LINKSLook for the purple links throughout thebook. Each link gives details of otherpages where related or additional factscan be found.

3

HOW TO USE THIS BOOK ............................................................................4–5

BODY SYSTEMS ........................................................................................................6–7• Integumentary • Skeletal • Muscular • Nervous • Sensory Respiratory • Circulatory • Digestive • Urinary • ReproductiveHormonal • Lymphatic • Immune

THE SKIN...........................................................................................................................8–9• Sense of touch • Fingertips • Sweat • Layers of the skin • Microsensors • Shed skin • Skin thickness • Main tasks of the skin • Size of the skin

HAIR AND NAILS ...........................................................................10–11• Nail parts • Growth of nails • Hair thickness • Structure of a hair • Eyebrows • Eyelashes • Growth of hair • Hair life cycle • Why have hair? • Why have nails?

MUSCLES & MOVEMENT ........................................................................12-13• Types of muscle • Muscle used for facial expressions • Inside a muscle • Power of muscles • How muscles work • Muscle records

THE SKELETON.....................................................................................................14-15• Size and variation • The coccyx • Cartilage • Bone strength• Tasks of the skeleton • Number of bones

BONES AND JOINTS .....................................................................................16-17• Parts of a bone • What a bone contains • Bone records • Ligaments • Synovial fluid • The knee joint • Different types of joint • Head movements

THE NERVOUS SYSTEM............................................................................18-19• Parts of the nervous system • Nerve cells • Nerve signals • Spinal cord • Nerve lengths

THE BRAIN ...............................................................................................................20-21• The cortex • Energy requirements • Blood supply to the brain • Brain parts • Size of the brain • Sleep • Left and right • Brain development through life

EYES AND SIGHT..............................................................................................22-23• Parts of the eye • How the eye sees • Cones • Blind spot • Moving the eye • Blinking

EARS & HEARING............................................................................................24-25• How we hear • Sections of the ear • Bones in the ear • Pitch• Sense of balance • Stereo hearing • Ear measurements • The loudness of sounds

NOSE & TONGUE..............................................................................................26-27• How we smell • Parts of the nose • Parts of the tongue• How we taste • Other tasks of the tongue

TEETH & JAW ........................................................................................................28-29• Numbers of teeth • Parts of a tooth • Plaque • When teeth grow• Chewing • Roof of the mouth • Saliva

LUNGS & BREATHING...............................................................................30–31• Size and shape of the lungs • Gases used • Breathing rates• Parts of the lungs • The voicebox • Speech

THE HEART..............................................................................................................32–33• Parts of the heart • Heart’s blood supply • Heart’s job • The pulse• Changing pulse rate through life • How the heart works • Size and shape • Typical day

CIRCULATORY SYSTEM.............................................................................34-35• Veins and arteries • Using oxygen • Types of blood vessels• Size and length of blood vessels • Journey times of blood• Blood pressure in blood vessels

BLOOD...........................................................................................................................36-37• Blood flow • Amount of blood in the body • Blood groups• Red blood cells • What is in blood?

DIGESTION...............................................................................................................38-39• The digestive tract • Digestive juices • Length of food’s journey • Faeces • Stomach • Appendix • Small intestine • Large intestine






STAGES OF LIFE...........................................50-51

• Growth rates • How an egg is fertilized • Embryo • Fetus • New baby • Puberty • Ageing

HORMONES..................................................52-53• Thyroid • Parathyroid • Pituitary • Pancreas • Thymus • Adrenals • Adrenaline• Other hormone making parts

LYMPH & IMMUNE SYSTEMS......................................................54-55• Lymph nodes • Lymph fluid • Lymphocytes• How the immune system works• Types of immunity

DISEASES & MEDICINES ...................56–57• Types of medicines • Medical drugs • Causes of illness and disease • Bacteria • Viruses • Protists • Micro-fungi • Medical specialists

GLOSSARY..........................................................58-59

INDEX......................................................................60–64

CONTENTS

• The digestive tract • Digestive juices • Length of food’s journey • Faeces • Stomach • Appendix • Small intestine • Large intestine






60





36b, 52b-d, 53c, 53dageing 51dalcohol 21d, 42a-caldosterone 53calleles 47a-callergies 56b, 56c-dalveoli 31a-camino acids 41aammonia 44a-damniotic fluid 50a-danaesthetics 56a, 57danaesthetist 57danalgesics 56aankles 15danti-emetics 56banti-inflammatories 56bantibiotic drugs 56b, 57aantibodies 37d, 54b,


52c-dantifungal 56bantigens 55a-c, 55dantihistamine 56bantipyretic 56bantiseptic 56bantitoxin 56bantiviral 56banus 6-7c, 38a, 39a-c

anvil bone (incus) 24aaorta 33d, 34a-b,


33dappendix 38a,

39daqueous humour

23a-carms 15d

arteries 20a, 33a-c,34, 35, 36a, 43b-c,

44b-darterioles 35a-c, 35d,

36bartificial acquired immunity 55d





20b-c



36-7, 40a, 45dclotting 6-7b, 36c-d, 37d,



20a, 30b-d, 37d, 40c-d,42a-c, 53




37a-cbones 6-7a, 16-17, 40a,



20-1, 24c-d, 37a-b,52b-d












17dcells 6-7a, 40, 49a-c,

50b-dsee also named types ofcell






INDEX





36b, 52b-d, 53c, 53dageing 51dalcohol 21d, 42a-caldosterone 53calleles 47a-callergies 56b, 56c-dalveoli 31a-camino acids 41aammonia 44a-damniotic fluid 50a-danaesthetics 56a, 57danaesthetist 57d

aaaaaaaaa

a

axaxax


IND

INTRODUCTION TO TOPIC

BOX HEADINGSLook for heading words linked to yourresearch to guide you to the right fact box.

CUTAWAY DIAGRAMSClear, accurate diagrams show howthe parts of the body fit together.

• See pages 36–37 forinformation on the blood.

DIGESTIVE SYSTEM






• Muscles contract to produce allforms of bodily movement.

• Sometimes combined with bones and joints as the musculoskeletal

system.

The body is often divided into body systems.

Each system, though performing specific

jobs, works together with the other systems.

Body systems are made from microscopic building

blocks, called cells. A typical cell is only 0.011 inches

across. There are about 10 trillion cells in the body.

There are many different kinds of cells, such as nerve cells

and muscle cells. Many cells of the same kind form tissue, such as nerve

and muscle tissue. Two or more different kinds of tissue create an organ,

like the brain, stomach, or kidney. Several organs working

together to carry out one major function, such as

digesting food, are known as a body system.

• The eyes, ears, nose, tongue, andskin make up the five main sets ofsensory organs.• Sensors inside the body monitorfor temperature, blood pressure,

oxygen levels, positions of joints, amount of stretch in muscles, and many other changes.



• The skin, hair, and nails.• Protectsinternal organs

from physicalwear, dirt, water,

sun’s rays, and harm.• Skin keeps in essential body fluids,


by sweating and flushing to loseheat, or going pale withgoosebumps to retain heat.

• Provides sense of touch (seeSensory System).

• Gets rid of small amounts of wastesubstances in sweat.

• The brain, spinal cord, and peripheral nerves.• Controls and coordinates all body processes, from breathing and heartbeat, to

making movements.• Allows mental processes, such as thoughts, recalling memories, and making decisions.

• Sensory nerves bring information from the sense organs and other sensors.• Motor nerves carry instructions to muscles about movement and to glands

about releasing their products.• Works with the hormonal system.







BODY SYSTEMS INTEGUMENTARYSYSTEM

NERVOUS SYSTEM

MUSCULAR SYSTEM

6

SKELETAL SYSTEM

• Mouth, teeth, throat, esophagus, stomach, intestines, rectum, and anus make up the digestivepassageway or tract.

• Liver, gall bladder, and pancreas are also part of the digestive system.• Digests food into nutrients tiny enough to take into the body.• Gets rid of leftovers as solid wastes.• Nutrients provide energy for all life processes and

raw materials for growth, maintenance, and repairingeveryday use.

DIGESTIVE SYSTEM






• Muscles contract to produce allforms of bodily movement.

• Sometimes combined with bones and joints as the musculoskeletal

system.

• Includes the nose, windpipe, main chestairways, and lungs.

• Obtains essential oxygen from the air aroundand passes it to the blood for distribution.

• Gets rid of waste carbondioxide, which would be

poisonous if it built up in the blood.

• Also provides theability to makevocal sounds

and speech.

• The heart, blood vessels, and blood.• The heart provides pumping power to send blood all

around the body.• Blood spreads vital oxygen, nutrients, hormones,

and other substances to all body parts.• Blood collects wastes and unwanted

substances from all body parts.• Blood clots seal wounds

and cuts.• Closely involved with the

immune system for fightingdisease.

CIRCULATORY (CARDIOVASCULAR) SYSTEM

• The lymph vessels, lymph nodes (glands), lymphducts, and lymph fluid.

• Gathers general body fluids from between cells and tissues.

• One-way flow channels fluid through thelymph network of nodes and vessels.

• Helps to distribute nutrients and collect wastes.

• Lymph fluid empties into blood system.• Closely linked with to immune system.

• Defends the body against invadingdangers such as bacteria, virusesand other microbes.

• Gets rid of debris in tissues fromnormal use.

• Helps the body recover fromdisease and illness.

• Helps repair injuries and normal use.• Keeps watch for problems and disease processes arising

inside the body, such as malignant (cancerous) cells.

• The only system which differs significantly in females and males.• The only system which is not working at birth, but starts to

function at puberty.• The male system produces sperm cells continually, millions per day.• The female system produces egg cells, about one every 28

days, during the menstrual cycle.• If an egg cell joins a sperm cell to form an embryo, the female

system nourishes this as the egg grows into a baby inside the womb.

The body is often divided into body systems.

Each system, though performing specific

jobs, works together with the other systems.

Body systems are made from microscopic building

blocks, called cells. A typical cell is only 0.011 inches

across. There are about 10 trillion cells in the body.

There are many different kinds of cells, such as nerve cells

and muscle cells. Many cells of the same kind form tissue, such as nerve

and muscle tissue. Two or more different kinds of tissue create an organ,

like the brain, stomach, or kidney. Several organs working

together to carry out one major function, such as

digesting food, are known as a body system.

• The eyes, ears, nose, tongue, andskin make up the five main sets ofsensory organs.• Sensors inside the body monitorfor temperature, blood pressure,

oxygen levels, positions of joints, amount of stretch in muscles, and many other changes.



• The kidneys, ureters, bladder, and urethra.• Filters blood to get rid of unwanted substances and wastes.• Forms unwanted substances and wastes into

liquid waste or urine.• Stores and releases urine.• Controls amount and concentration

of blood and body fluids, called water balance, by adjusting amount of water lost in urine.

• About ten main parts called endocrine or hormone-making glands.

• Some organs with other main tasks, like thestomach and heart, also make hormones.

• Hormones spread around the body in blood.• Closely linked to the nervous system for

coordinated control of inner-body processes.• Closely linked with reproductive system..

• The skin, hair, and nails.• Protectsinternal organs

from physicalwear, dirt, water,

sun’s rays, and harm.• Skin keeps in essential body fluids,


by sweating and flushing to loseheat, or going pale withgoosebumps to retain heat.

• Provides sense of touch (seeSensory System).

• Gets rid of small amounts of wastesubstances in sweat.

• The brain, spinal cord, and peripheral nerves.• Controls and coordinates all body processes, from breathing and heartbeat, to

making movements.• Allows mental processes, such as thoughts, recalling memories, and making decisions.

• Sensory nerves bring information from the sense organs and other sensors.• Motor nerves carry instructions to muscles about movement and to glands

about releasing their products.• Works with the hormonal system.







RESPIRATORY SYSTEMBODY SYSTEMS INTEGUMENTARYSYSTEM

SENSORY SYSTEM

URINARY SYSTEM

LYMPHATIC SYSTEMNERVOUS SYSTEM

HORMONAL (ENDOCRINE) SYSTEM

IMMUNE SYSTEM

MUSCULAR SYSTEM

6 7

SKELETAL SYSTEM

REPRODUCTIVE SYSTEM

8

An average patch of skin0.15 sq. in. (the size of afingernail) contains:

• 5 million microscopic cells of at least 12 main kinds.

• 100 tiny holes, called pores, forreleasing sweat.

• 1,000 micro-sensors of about six main shapes for detectingvarious features of touch.

• more than 100 hairs.

• About 3.2 ft. of blood vessels.

• About 20 in. of micronerves.

• About 100 of the tiny glandsthat make sebum, a naturalwaxy-oily substance that keeps skin supple and fairlywaterproof.

THE SKIN When you look at yourself in the mirror, most of what you see—skin,

hair and nails—is not living. Just underneath this dead surface,

however, skin is very much alive, and very busy, too—as you know

if you’re unlucky enough to scratch or cut yourself. Skin is the body’s largest

single organ. It has at least ten main tasks, which include providing your sense

of touch. It wears away every month—but it replaces itself every month, too.

Your sense of touch or feelingis more complicated than itseems. It is not just a singlesense, detecting physicalcontact. It is a multi-sensedetecting:

• Light contact, such as a brushfrom a feather.

• Heavy pressure, such as beingpushed or squeezed hard.

• Cold, like an ice-cube.

• Heat, such a hot water.

• Movement, including tiny, fastvibrations. Your fingertip skin candetect vibrations that are too small for your eyes to see.

• Surface texture, such as roughwood or smooth plastic.

• Moisture content, from dry sand to wet mud.

• Skin on the fingertips has morethan 465 microsensors persquare inch, to give themost sensitive touch.

• It has more sweatglands that makea thin layer ofsweat on the skinthat helps you to gripbetter.

• It also has tiny ridges or swirls togive even better grip. These formthe pattern of your fingerprints.

• Every set of fingerprints for everyperson around the world is

different—even betweenidentical twins.

The skin is a tough but flexiblelayer that covers the entire

body. It helps to controltemperature and protects

internal organs from damage.

WHERE IN THE BODY?

Total number of sweat glands 3–5 million

Total length of tubes in all sweat glands stretched outstraight and joined end-to-end 31 miles

Amount of sweat on average day 10–17 fl. oz.

Amount of sweat on a cold day 2.3 fl. oz.

SWEAT FACTS

epidermis

dermis

A thin layer ofsweat on the

fingertips helps you grip objects better.

Lowest layer - hypodermis• Contains mainly body fat, which

works as a cushion against knocksand pressure.

• Works as an insulator to keep inbody warmth.

Middle layer - dermis• Contains sweat glands, hair roots

(follicles), most of the microsensorsfor touch, and tiny blood vesselscalled capillaries.

• Also contains fibers of thesubstances collagen for strengthand elastin for elasticity.

sensory nerve

blood vessels

body fat

A person can lose 10.5–15 pintsof sweat before the body suffers from the loss of important saltsand minerals.

DANGEROUS SWEAT

Outermost layer - epidermis • Varies greatly in thickness from

0.019 to more than 0.2 in.

• If it has lots of wear, such asusing hands often or walkingbarefoot, it can make itself twiceas thick as normal, for extraprotection. This is called a callus.

Microscopic cells at its base multiplyfast, fill with the tough substancekeratin, move outward, becomeflatter and die, and form the surfacelayer which is continually rubbedaway.

hair root

SKIN MICROPARTS

TOUCH

Wearing warm clothes in winter helps protect our skin from feeling the cold.

EXTRA SENSITIVE

8 9

Protection

• Provides protection from knocksand bumps.

• Keeps out dirt, germs, andliquids. like water.

• Shields the body from the sun’s dangerous rays(especially ultraviolet, UV),perhaps by going darker(suntan).

Keeps fluids in

• Keeping in valuable bodyfluids, minerals, and salts.

Touch

• Provides sense of touch.

Temperature control

• Cools the body if it gets too hot.

• Keeps heat inside the body in cold conditions.

Vitamin D

• Produces an important nutrient,vitamin D, that keeps youhealthy.

Waste removal

• Removes of some wasteproducts (through sweat).

Anti-germ layer

• Produces germ-killingsubstances to form a layer on skin.

MAIN TASKS OF THES K I N

LAYERS OF THE SKIN

An average patch of skin0.15 sq. in. (the size of afingernail) contains:

• 5 million microscopic cells of at least 12 main kinds.

• 100 tiny holes, called pores, forreleasing sweat.

• 1,000 micro-sensors of about six main shapes for detectingvarious features of touch.

• more than 100 hairs.

• About 3.2 ft. of blood vessels.

• About 20 in. of micronerves.

• About 100 of the tiny glandsthat make sebum, a naturalwaxy-oily substance that keeps skin supple and fairlywaterproof.

THE SKIN When you look at yourself in the mirror, most of what you see—skin,

hair and nails—is not living. Just underneath this dead surface,

however, skin is very much alive, and very busy, too—as you know

if you’re unlucky enough to scratch or cut yourself. Skin is the body’s largest

single organ. It has at least ten main tasks, which include providing your sense

of touch. It wears away every month—but it replaces itself every month, too.

Your sense of touch or feelingis more complicated than itseems. It is not just a singlesense, detecting physicalcontact. It is a multi-sensedetecting:

• Light contact, such as a brushfrom a feather.

• Heavy pressure, such as beingpushed or squeezed hard.

• Cold, like an ice-cube.

• Heat, such a hot water.

• Movement, including tiny, fastvibrations. Your fingertip skin candetect vibrations that are too small for your eyes to see.

• Surface texture, such as roughwood or smooth plastic.

• Moisture content, from dry sand to wet mud.

• Skin on the fingertips has morethan 465 microsensors persquare inch, to give themost sensitive touch.

• It has more sweatglands that makea thin layer ofsweat on the skinthat helps you to gripbetter.

• It also has tiny ridges or swirls togive even better grip. These formthe pattern of your fingerprints.

• Every set of fingerprints for everyperson around the world is

different—even betweenidentical twins.

• The largest touch micro-sensorsare called Pacinian sensors.They have many layers like tinyonions and are up to 0.019 in.across. They detect hard pressure.

• The smallest microsensors are 100times smaller and feel light touch.

MICROSENSORS

AreaA typical adult’s skin, taken off and ironed flat, would cover some6.5 sq. feet—about the area of a single bed or a small shower curtain.

Weight The weight of the skin is about6.6–8.8 lbs. for a typical adult—twice as heavy as the next-largestorgan, the liver.

S I Z E O F T H ES K I N

The skin is a tough but flexiblelayer that covers the entire

body. It helps to controltemperature and protects

internal organs from damage.

WHERE IN THE BODY?

Total number of sweat glands 3–5 million

Total length of tubes in all sweat glands stretched outstraight and joined end-to-end 31 miles

Amount of sweat on average day 10–17 fl. oz.

Amount of sweat on a cold day 2.3 fl. oz.

SWEAT FACTS

• Each minute about 50,000 tinyflakes of skin are rubbed off orfall from the body.

• This loss is natural and is madeup by microscopic cells at thebase of the epidermis multiplyingrapidly.

• This happens so fast that theepidermis replaces itself aboutevery month.

• Over a lifetime the body shedsmore than 88 lbs. of skin.

Skin makes itself thicker where it is worn or rubbed more.On average:

Soles of feet - 0.2 in. or moreBack 0.1–0.15 in.Palms of hands - 0.08–0.15 in.Scalp on head - 0.06 in.Fingertips - 0.04 in.Average body 0.04–0.08 in.Eyelids - 0.019 in.

SKIN THICKNESS

epidermis

dermis

A thin layer ofsweat on the

fingertips helps you grip objects better.

Lowest layer - hypodermis• Contains mainly body fat, which

works as a cushion against knocksand pressure.

• Works as an insulator to keep inbody warmth.

Middle layer - dermis• Contains sweat glands, hair roots

(follicles), most of the microsensorsfor touch, and tiny blood vesselscalled capillaries.

• Also contains fibers of thesubstances collagen for strengthand elastin for elasticity.

sensory nerve

blood vessels

body fat

A person can lose 10.5–15 pintsof sweat before the body suffers from the loss of important saltsand minerals.

DANGEROUS SWEAT

Outermost layer - epidermis • Varies greatly in thickness from

0.019 to more than 0.2 in.

• If it has lots of wear, such asusing hands often or walkingbarefoot, it can make itself twiceas thick as normal, for extraprotection. This is called a callus.

Microscopic cells at its base multiplyfast, fill with the tough substancekeratin, move outward, becomeflatter and die, and form the surfacelayer which is continually rubbedaway.

hair root

• See pages 22–23 forinformation on eye.

• See pages 36–37 forinformation on blood circulation.

SKIN MICROPARTS

TOUCH

Wearing warm clothes in winter helps protect our skin from feeling the cold.

EXTRA SENSITIVE

SHED SKIN

0.2

0.1

hair shaft

HAIR GROWTH

10

W H Y H A V E I T ?

• After this final slow down, theyusually fall out and are replacedby new hairs growing up fromthe same follicles in the skin.

• This means, on average, about100 hairs are lost from the headevery day.

• In eyebrow hairs, the life cyclelasts about 20 weeks.

• In eyelash hairs, the life cyclelasts around 10 weeks.

• In scalp hairs, this life cycle lastsup to 5 years.

HAIR & NAILS

• Scalp hairs grow 0.011–0.015 in.each day, which is almost 0.5 in.each month.

• Eyebrow hairs grow slowly, only0.0005 in. per day, reaching agreatest length of 0.2 in.

• Eyelash hairs grow at a similar rateto eyebrow hairs, but usually stopgrowing at 0.27–0.31 in. long.

Hairs and nails, like the epidermis, the outer layer of skin, are dead.

Your body has hairs all over, except for a few places, like your

palms, the palm sides of your fingers, and the soles of your feet.

However, some hairs grow thicker and longer, and so we notice them more.

These are the hairs on the head, eyebrows, and eyelashes. As we grow up,

hairs also appear under the arms, called axillary hair, and between the legs.

Nail plateThe main flat part of the nail.

Free edgeThe end of the nail which you trim, not attached to the underlying finger or toe.

Nail bedThe underside of the nail plate, which isattached to the underlying flesh but slidesslowly along as it grows.

LunulaThe pale ‘half-moon’ where the youngest partof the nail emerges from the flesh of the fingeror toe.

EponychiumThe cuticle fold where the nail base disappearsunder the flesh of the finger or toe.

Nail root

The growing part of the nail, hidden in the fleshof the finger or toe.

• Most nails grow about 0.019 in.each week.

• In general, fingernails grow fasterthan toenails.

• Nails grow faster in summer thanin winter.

• If you’re right-handed, nails onyour right hand grow faster thanthose on your left, and the otherway round if you’re left-handed.

NAIL GROWTH

WHERE IN THE BODY?

Eyebrow hairsHelp to stop sweat dripping into the eyes.

Eyelash hairsHelp to whisk away bits of windblowndust, dirt, and pests like insects fromth e eyes.

• Most scalp hairs are around0.0019 in. thick, so 500 in arow would be almost 1 in.thick.

• Light colored hairs are usuallythinner than dark hairs.

• Eyelashes are thicker, up to0.003 in.

Finger nails have many different parts.

inches of hair growth per month

NUMBER OF HAIRS

Hair is found almost all over our bodies.

Nails grow at the end of each toe and finger.

Most kinds of hairs grow for a time, gradually slow down in growth rate, then hardly grow at all.

EYEBROWS AND EYELASHES

• See pages 22–23 forinformation on eyes.

NAIL PARTS

THE THICKNESS OF A HAIR

WHY HAVE EYELASHESAND EYEBROWS?

0.5 in

0.25in

0in

Scalp Hair

Eyebrow Eyelash

Different kinds of hairs grow at different rates.

• Because most scalp hairs growfor only 3-5 years, theirmaximum length is 20–31in. before they fall out andare replaced.

• However, some people haveunusual hair that falls outmuch less often, and canreach lengths of 26 feet.

Hair growth in thin, fairhair is slower than in thick,dark hair.

HAIR GROWTH

10 11

N A I L SWHY HAVE THEM?

A nail is a strong, stiff,dead, flat plate made of the same dead substance as hairs, keratin. Each nailacts as a flat, rigid pad onthe back of the fingertip.

Touch • When you press gently on an

object, the fingertip is squeezedbetween it and the nail.

• This makes it easier to judgepressure and the hardness of theobject. Without a nail, the wholefingertip would bend back.

Scratching• You also use nails to scratch and

get rid of objects on the skin.

• Hairs are glued-together rods of dead, flattened,microscopic cells filled withthe tough, hard bodysubstance, called keratin.

• A hair grows at its root, whichis buried in a pocket-like pitin the skin, called the follicle.

• Extra cells are added to theroot, which pushes the rest of the hair up out of the skin.

• The part of the hair above theroot is called the shaft.

Protection• Head hair protects against bangs

and bruises.

• It also shields the top of the head,and the delicate brain inside, from heat or cold.

Warmth• Body hairs stand on end when

you’re cold, each pulled by a tinymuscle attached to its root, calledthe erector pili muscle.

• These “goosebumps” around thebody helps to trap air and keepsin body warmth.

Safety• Our hair can also stand on end

when we feel frightened. Whenour body hairs were longer, inprehistoric times, the ‘hair-raising’also made us look bigger andmore impressive to enemies.

H A I RW H Y H A V E I T ?

• After this final slow down, theyusually fall out and are replacedby new hairs growing up fromthe same follicles in the skin.

• This means, on average, about100 hairs are lost from the headevery day.

• In eyebrow hairs, the life cyclelasts about 20 weeks.

• In eyelash hairs, the life cyclelasts around 10 weeks.

• In scalp hairs, this life cycle lastsup to 5 years.

HAIR & NAILS

• Scalp hairs grow 0.011–0.015 in.each day, which is almost 0.5 in.each month.

• Eyebrow hairs grow slowly, only0.0005 in. per day, reaching agreatest length of 0.2 in.

• Eyelash hairs grow at a similar rateto eyebrow hairs, but usually stopgrowing at 0.27–0.31 in. long.

Hairs and nails, like the epidermis, the outer layer of skin, are dead.

Your body has hairs all over, except for a few places, like your

palms, the palm sides of your fingers, and the soles of your feet.

However, some hairs grow thicker and longer, and so we notice them more.

These are the hairs on the head, eyebrows, and eyelashes. As we grow up,

hairs also appear under the arms, called axillary hair, and between the legs.

Nail plateThe main flat part of the nail.

Free edgeThe end of the nail which you trim, not attached to the underlying finger or toe.

Nail bedThe underside of the nail plate, which isattached to the underlying flesh but slidesslowly along as it grows.

LunulaThe pale ‘half-moon’ where the youngest partof the nail emerges from the flesh of the fingeror toe.

EponychiumThe cuticle fold where the nail base disappearsunder the flesh of the finger or toe.

Nail root

The growing part of the nail, hidden in the fleshof the finger or toe.

• Most nails grow about 0.019 in.each week.

• In general, fingernails grow fasterthan toenails.

• Nails grow faster in summer thanin winter.

• If you’re right-handed, nails onyour right hand grow faster thanthose on your left, and the otherway round if you’re left-handed.

NAIL GROWTH

WHERE IN THE BODY?

hair folliclehair shaft

Eyebrow hairsHelp to stop sweat dripping into the eyes.

Eyelash hairsHelp to whisk away bits of windblowndust, dirt, and pests like insects fromth e eyes.

• Most scalp hairs are around0.0019 in. thick, so 500 in arow would be almost 1 in.thick.

• Light colored hairs are usuallythinner than dark hairs.

• Eyelashes are thicker, up to0.003 in.

• Hair growth is faster at nightthan during the day.

• Hair growth is faster in summerthan in winter.

• Hair growth is faster around the ages of 15–25 years thanany other time.

FASTER HAIRGROWING

Finger nails have many different parts.

• See pages 8–9 forinformation on THE SKIN.

inches of hair growth per month

The number of hairs on the head varies according to the color of the hair. In a typical adult, thenumber is:

Fair hair 130,000

Brown 110,000

Black 100,000

Red 90,000

NUMBER OF HAIRS

Hair is found almost all over our bodies.

Nails grow at the end of each toe and finger.

Most kinds of hairs grow for a time, gradually slow down in growth rate, then hardly grow at all.

EYEBROWS AND EYELASHES

• See pages 22–23 forinformation on eyes.

• See page 51 for SIGNS OF AGING

HAIR LIFE CYCLES

NAIL PARTS

THE THICKNESS OF A HAIR

WHY HAVE EYELASHESAND EYEBROWS?

HAIR STRUCTURE AND THICKNESS

0.5 in

0.25in

0in

Scalp Hair

Eyebrow Eyelash

Different kinds of hairs grow at different rates.

• Because most scalp hairs growfor only 3-5 years, theirmaximum length is 20–31in. before they fall out andare replaced.

• However, some people haveunusual hair that falls outmuch less often, and canreach lengths of 26 feet.

Hair growth in thin, fairhair is slower than in thick,dark hair.

12

INSIDE A MUSCLEMUSCLES AND MOVEMENT

• All muscles need energy to work,which is brought by the blood inthe form of blood sugar (glucose).

• You use about 40 facial muscles to frown, but only half as many to smile.

Muscles power all of your body’s movements, from blinking to

jumping high in the air. Muscle actions are controlled by messages

from your brain along nerves called motor nerves. Muscles are the

body’s largest single system and are found throughout the body. Half of a

grown human being’s body weight is from their muscles.

The body has three mainkinds of muscles: skeletal,visceral, and cardiac.

• Skeletal muscles are mostlyattached to the bones of theskeleton and pull on them tomake you move.

• These are the ones we normally mean when we talk about muscles.

• Skeletal muscles are also called voluntary muscles,because you can control them at will just by thinking.

• Skeletal muscles are also calledstriped or striated muscles becauseunder the microscope they have apattern of stripes or bands.

• Visceral muscles form sheets, layers, or tubes in the walls of the inner body parts (viscera) like the stomach and bladder.

• Visceral muscles are alsocalled involuntarymuscles because theywork automatically.

• Visceral muscles are also calledsmooth muscles becauseunder the microscope they lack any pattern of stripes or bands.

• The third type of muscle is cardiac muscle, which forms the walls of the heart.

Muscles are found throughout the body. They help

us to move, from walking tolifting objects.

WHERE IN THE BODY?

• See pages 36–37 forinformation on BLOOD. • See pages 32–33 for information on THE HEART.

• See pages 20–21 for information on the brain.

SAVE ENERGY – GIVE A SMILE

Skeletal muscles, seen from the back.

TYPES OF MUSCLE

MUSCLES THAT MAKE FACESWe use our muscles to communicate and send information—and not just by speaking,which uses about 40 muscles. We also use muscles for facial expressions.

Muscle name Site What it does ExpressionFrontalis Forehead Raises eyebrows Surprise

Procerus Between eyes Pulls eyebrows in and down Stern, concentration

Auricularis Above and to side of ear Wiggles ear (only for some people)

Buccinator Cheek Moves cheek Blowing, sucking

Risorius Side of mouth Pulls corner of mouth Grin

Depressor labii Under lip Pulls lower lip down Frown

Face muscles allow us to make a huge range of expressions.

Muscle fibrilsEven thinner parts,forming a bundle withineach muscle fiber.

frontalis

levator labii superioris

orbicularis oris

depressor labii inferioris

12 13

MUSCLER E C O R D S

• There are about 640 mainskeletal muscles.

• They form about two-fifths ofthe body weight in adultmen, and slightly less, aboutone-third of body weight, inadult women, girls, andboys.

• Plenty of exercise and activitymakes muscles grow biggerand stronger. They can formup to half of body weight.

MUSCLER E C O R D S

BulkiestThe gluteus maximus, forming most of the buttock. It works when youpull your thigh back to push yourbody forward when you walk, run, and jump.

Smallest

The stapedius, deep in the ear. When the ear detects very loudnoises it pulls on the body’ssmallest bone, the stirrup (stapes),to prevent it moving too much anddamaging the delicate inner partsof the ear.

Longest

The sartorius, which runs from the side of the hip down across thefront of the thigh to the inner side of the knee.

Most powerful for its size

The masseter, which runs from thecheekbone to the lower side of the lower jaw and bulges when you chew.

Busiest

The orbicularis oculi, better knownas the eyelid muscles. They workup to 50,000 times each day asyou blink and wink.

Biggest tendon

The calcaneal tendon, which joins the calf muscles to the heel bone. It takes the strain when you standon tip-toe and is often called theAchilles tendon.

INSIDE A MUSCLEMUSCLES AND MOVEMENT

• All muscles need energy to work,which is brought by the blood inthe form of blood sugar (glucose).

• You use about 40 facial muscles to frown, but only half as many to smile.

Muscles power all of your body’s movements, from blinking to

jumping high in the air. Muscle actions are controlled by messages

from your brain along nerves called motor nerves. Muscles are the

body’s largest single system and are found throughout the body. Half of a

grown human being’s body weight is from their muscles.

The body has three mainkinds of muscles: skeletal,visceral, and cardiac.

• Skeletal muscles are mostlyattached to the bones of theskeleton and pull on them tomake you move.

• These are the ones we normally mean when we talk about muscles.

• Skeletal muscles are also called voluntary muscles,because you can control them at will just by thinking.

• Skeletal muscles are also calledstriped or striated muscles becauseunder the microscope they have apattern of stripes or bands.

• Visceral muscles form sheets, layers, or tubes in the walls of the inner body parts (viscera) like the stomach and bladder.

• Visceral muscles are alsocalled involuntarymuscles because theywork automatically.

• Visceral muscles are also calledsmooth muscles becauseunder the microscope they lack any pattern of stripes or bands.

• The third type of muscle is cardiac muscle, which forms the walls of the heart.

This list shows the power ofthe body’s muscle comparedto various machines, in watts(the scientific units of power).

Laser-pen pointer 0.002

Heart by itself 2

All the body’s muscles working hard 100

Family car on the highway 100,000

Space shuttle 10,000 million

MUSCLEPOWER COMPARED

Muscles are found throughout the body. They help

us to move, from walking tolifting objects.

WHERE IN THE BODY?

Actin

EpimysiumThe muscle’s outercovering.

Muscle FiberLong, thin part, about asthick as a hair.

Exercise can increase the size ofmuscles, but they have no effecton the actual number of musclesor the number of muscle cells—this stays the same.

• Some people have very smallversions of certain muscles ornone at all. This is part of thenatural variation betweendifferent people.

• For example, a few people lackthe thin, sheet-like muscle in theneck, called the platysma.

INDIVIDUALVARIATIONS

A muscle is a bundle of fibers. These bundlesare called fascicles. Within each fiber is agroup of fibrils. A single fibril contains myosin and actin filaments. These slide past each other to shorten the muscle.

• See pages 36–37 forinformation on BLOOD.

Myosin

• See pages 32–33 for information on THE HEART.

Muscles work by contracting andpulling their ends closer together.

• In most skeletal muscles, the endstaper to rope-like tendons, whichare joined firmly to bones.

• Muscles cannot push or forcefullyget longer, they are stretchedlonger when other muscles workelsewhere.

• Muscles contain two bodysubstances, or proteins, called actinand myosin, which are shaped likelong threads.

• In each muscle, millions of thesethreads slide past each other tomake the whole muscle shorten.

• Most muscles can shorten orcontract to about two-thirds theirresting length.

• A muscle bulges in the middlewhen it shortens but its overall size or volume does not change.

• See pages 20–21 for information on the brain.

• See pages 40–41 FOOD AND NUTRIENTS.

SAVE ENERGY – GIVE A SMILE

Skeletal muscles, seen from the back.

TYPES OF MUSCLE

MUSCLES THAT MAKE FACESWe use our muscles to communicate and send information—and not just by speaking,which uses about 40 muscles. We also use muscles for facial expressions.

Muscle name Site What it does ExpressionFrontalis Forehead Raises eyebrows Surprise

Procerus Between eyes Pulls eyebrows in and down Stern, concentration

Auricularis Above and to side of ear Wiggles ear (only for some people)

Buccinator Cheek Moves cheek Blowing, sucking

Risorius Side of mouth Pulls corner of mouth Grin

Depressor labii Under lip Pulls lower lip down Frown

Face muscles allow us to make a huge range of expressions.

Muscle fibrilsEven thinner parts,forming a bundle withineach muscle fiber.

HOW MUSCLES WORK

frontalis

levator labii superioris

orbicularis oris

depressor labii inferioris

Muscle fascicleBundle of musclefibers.

14

B O N E STHE SKELETON

There are three bones inthe body not joined to anyother bone.HyoidA U-shaped bone in the front of theupper neck, near the throat and thebase of the tongue.

Kneecap or patellaThis is inside a muscle tendon andslides over the front of the kneejoint, helping to protect it.

BONES NOT JOINED TO OTHER BONES

Your skeleton consists of all the bones in your body—over 200 of

them. It’s like an inner framework that supports the softer body

parts such as organs, nerves, and blood vessels. Your skeleton is not

fixed and stiff. It is a moving framework that muscles pull into hundreds of

different positions every day.

Imagining our bodies as various everyday objects can helpus to understand how they work.

Bones are the found throughoutthe body. Flexible parts of thebody, such as fingers and toes,

have more bones.

WHERE IN THE BODY?

The skeleton provides some protection for vital body parts,but it is helpful to provide extra protection, such as a helmet

when riding a bike.

Monkeys and humans are descended from the same distant ancestors.

SIZE AND VARIATIONS

Our bones are a strong inner framework that hold up the soft inner parts of the body.

SKELETON STRENGTH

The lowest part of the backboneis called the coccyx.It’s made of three to five smallerbones fused together into one,shaped like a small prong. It is all

that is left of the long tail that ourvery distant ancestors had,millions of years ago, when theylooked like monkeys and lived intrees.

TAIL END

• There is no truth in the old belief that men andwomen have differentnumbers of ribs. Both have 24ribs, as 12 pairs.

• However, the total number ofbones varies slightly as part of natural differences betweenpeople.

• For example, about oneperson in 20 (man or woman)has an extra pair of ribs,

making 21 pairs instead ofthe usual 20.

• There are more bones, over300, in the skeleton of a baby.

• As the baby grows, some ofthese enlarge and fusetogether to make bigger single bones.

• The skeleton forms about one-seventh of the body’stotal weight.

• See pages 50–51 for information on STAGES OF LIFE.

LeversThe long bones of the arms andlegs work like levers, with theirpivot, or fulcrum, at the joint.

A bicycle chainThe many separate bones orvertebrae of the backbone onlymove slightly compared to each other. But over the wholebackbone, this movement addsup to allow bending double, like the links of a bicycle chain.

A cageThe ribs work like the moveablebars of a cage. This protects theheart and lungs, yet gets biggerand smaller as the lungs breathein and out.

An eggshellThe dome shape of the craniumaround the brain is a very strongdesign, like an eggshell. Anysharp ridges or corners wouldweaken it.

• See pages 16–17 for information on BONES AND JOINTS.

WHAT ARE BONES LIKE?

14 15

A human skeleton contains,on average, 206 bones.They are divided in differentgroups through the body:

Skull

Cranium (brain case) 8

Face 14

Ear 3 tiny bones each

Total: 28 bones

Throat (hyoid bone) 1

Backbone

Neck (cervical vertebrae) 7

Chest (thoracic vertebrae) 12

Lower back (lumbarvertebrae) 5

Base of back (sacrum,coccyx) 2

Total: 26 bones

Rib cage

Ribs 24

Breastbone 1

Total: 25 bones

Arms

Shoulder 2

Upper arm 1

Forearm 2

Wrist 8

Palm 5

Fingers and thumb 14

Total: 32 bones in each arm(includes hand)

Legs

Hip 1

Thigh and knee 2

Shin 2

Ankle 7

Sole of foot 5

Toes 14

Total: 31 bones in each leg(includes foot)

N U M B E R S O FB O N E STHE SKELETON

The main tasks of theskeleton are to:• Hold up the body, giving support

to softer parts.• Allow the body to move when

pulled by muscles.• Provide openings for the nose and

mouth to breathe and eat.• Protect certain body parts, for

example, the upper skull aroundthe brain, the front skull aroundmost of the eyes, and the ribsaround the lungs and chest.

• Store many body minerals, suchas calcium and magnesium, fortimes when food is scarce andthese minerals are in short supplyfor other body processes, likesending nerve messages.

• Make new microscopic cells for theblood, at the rate of 3 million everysecond. These cells are produced inthe soft jelly-like bone marrowfound in the centers of some bones.

There are three bones inthe body not joined to anyother bone.HyoidA U-shaped bone in the front of theupper neck, near the throat and thebase of the tongue.

Kneecap or patellaThis is inside a muscle tendon andslides over the front of the kneejoint, helping to protect it.

BONES NOT JOINED TO OTHER BONES

Your skeleton consists of all the bones in your body—over 200 of

them. It’s like an inner framework that supports the softer body

parts such as organs, nerves, and blood vessels. Your skeleton is not

fixed and stiff. It is a moving framework that muscles pull into hundreds of

different positions every day.

Imagining our bodies as various everyday objects can helpus to understand how they work.

• Most bones of the skeleton beginnot as real bone, but as a slightlysofter, bendier, smooth substancecalled cartilage (gristle).

• In a developing baby, the shapesof the eventual bones form first ascartilage.

• Then, as the baby grows into achild, the cartilage shapes becomehardened into real bones.

• Even in the adult skeleton, somebones are partly cartilage.

• For example, the front end of each rib, where it joins to thebreastbone, is made not of bonebut of cartilage called costalcartilage.

• The nose and ears are mainlycartilage, not bone, which is whythey are slightly flexible.

NOT ALL BONE

• The bones of the skeleton arestronger, size for weight, thanalmost every kind of wood orplastic.

• If the skeleton was made ofsteel, it would weigh four timesas much.

• The thigh bone can stand apressure of 21 tons per sq. in.when we jump and land.

• The skeleton can also menditself, which no kind of plastic or metal can.

Bones are the found throughoutthe body. Flexible parts of thebody, such as fingers and toes,

have more bones.

WHERE IN THE BODY?

The skeleton provides some protection for vital body parts,but it is helpful to provide extra protection, such as a helmet

when riding a bike.

Monkeys and humans are descended from the same distant ancestors.

Our skeleton is made ofliving bones that can mend

themselves if broken.

Most of a baby’s skeleton is made of cartilage, not bone.

SIZE AND VARIATIONS

Our bones are a strong inner framework that hold up the soft inner parts of the body.

SKELETON STRENGTH

The lowest part of the backboneis called the coccyx.It’s made of three to five smallerbones fused together into one,shaped like a small prong. It is all

that is left of the long tail that ourvery distant ancestors had,millions of years ago, when theylooked like monkeys and lived intrees.

TAIL END

• There is no truth in the old belief that men andwomen have differentnumbers of ribs. Both have 24ribs, as 12 pairs.

• However, the total number ofbones varies slightly as part of natural differences betweenpeople.

• For example, about oneperson in 20 (man or woman)has an extra pair of ribs,

making 21 pairs instead ofthe usual 20.

• There are more bones, over300, in the skeleton of a baby.

• As the baby grows, some ofthese enlarge and fusetogether to make bigger single bones.

• The skeleton forms about one-seventh of the body’stotal weight.

• See pages 50–51 for information on STAGES OF LIFE.

LeversThe long bones of the arms andlegs work like levers, with theirpivot, or fulcrum, at the joint.

A bicycle chainThe many separate bones orvertebrae of the backbone onlymove slightly compared to each other. But over the wholebackbone, this movement addsup to allow bending double, like the links of a bicycle chain.

A cageThe ribs work like the moveablebars of a cage. This protects theheart and lungs, yet gets biggerand smaller as the lungs breathein and out.

An eggshellThe dome shape of the craniumaround the brain is a very strongdesign, like an eggshell. Anysharp ridges or corners wouldweaken it.

• See pages 16–17 for information on BONES AND JOINTS.

WHAT ARE BONES LIKE?

SKELETON’S MAIN TASKS

16

PARTS OF A BONEBONES & JOINTS

• The word skeleton comes from anancient word meaning dried up. Butliving bones are not dry, they areabout one-quarter water. (Overall,the body is two-thirds water.)

• The main minerals in bone arecalcium, phosphate, and

carbonate. These form tiny crystalswhich give bone its hardness andstiffness.

• Bone also contains tiny fibers ofthe substance collagen, whichmakes it slightly flexible underpressure, and less likely to snap.

• If a bone is soaked in a specialacid chemical, the crystals ofcalcium phosphate and calciumcarbonate are removed. Only thecollagen fiber are left. This meansthat it is so flexible that a longbone like the upper-arm bone canbe tied in a knot.

BONE RECORDS

Your skeleton holds you up, but you would not be able to move if it

was not for the joints that link your bones together. More than half of

your body’s bones—112 out of 206—are in your wrists, hands,

fingers, ankles, feet, and toes. So are more than half of your 200-plus joints.

Your bones, muscles and joints work so closely together that they are

sometimes viewed as a single system, called the musculoskeletal system.

The two topmost backbones(cervical vertebrae), justunder the skull, have specialjoint designs. They allow thehead to make importantmovements.

• The axis (uppermost) backbonehas a curved shape like a saddle.It allows the head to tilt to theside and nod.

• The atlas (second uppermost)backbone is more like a ring andallows the head to turn or rotateto look to the side.

Joints allow the skeleton to move. They can be found

all over the body.

WHERE IN THE BODY?

Nodding and shaking yourhead is only possible with

two special joint designs inthe backbone.

HeadThe rounded end of

a long bone.

TubercleA lumpy projection on abone, usually where a

muscle is attached.

ShaftThe slimmer middlepart of a long bone.

PeriosteumThe outer covering wrapped allaround the bone.

ForamenSmall hole in a bone, where a nerveor blood vessel passes inside.

Compact boneVery strong, hard outer layer ofbone, like a shell.

Osteons (Haversian systems)Tiny cells of bone substance bundledand glued together to makecompact bone.

Spongy or cancellous boneInner layer of a bone, under thecompact bone, that has holes like a sponge.

MarrowJelly-like substance in the center of most bones.

Red marrowFound in all bones of a baby, butonly in the long bones of the armsand legs, ribs, backbone,breastbone and upper skull in anadult. Makes new microscopic cellsfor the blood.

Yellow marrowIn adults, found mainly in smallerbones of the hands and feet.Contains fat for use as an energyreserve, but can change to redmarrow if needed.

Bones are held together at a joint by stretchy straps calledligaments, which stop themmoving too far or coming apart. If the bones slip and come out oftheir usual position, a dislocationoccurs.

Ligament Muscle

During long space flights, the lackof gravity puts bones under lesspreasure than they are on Earth.The bones start to lose mineralsand become weaker. Astronautsexercise regularly to keep their

bones strong.

PARTS OF A BONE

LIGAMENTS YES AND NO

BONE MAKE UP

Your single biggest joint, the knee, has an unusual design with extra cartilages and ligaments.

• In addition to the cartilage covering theends of the thigh and shin bones, the cartilage covers the knee withtwo pieces of moon-shapedcartilage.

• The cartilage pieces are calledmenisci and help the knee tolock straight so you can standup easily.

• When atheletes have tornknee cartilage, it’s usually oneof these menisci which isdamaged.

• The knee has two strong sets of ligaments, the lateral

ligaments on the outer side andthe medial ligaments on the

inner side (next to the other knee).

• As well as these, it hastwo ligaments inside, keeping

the ends of the bones very closetogether.

• These two ligaments form an X-like shape and are called

cruciate ligaments.

Exercising and playing sportscan sometimes damage

your knee. It isimportant to always

warm up.

• See pages 40–41 FOOD AND NUTRIENTS

16 17

D E S I G N O F T H EJ O I N T

The different designs of yourbody’s joints are sometimescompared to machines andmechanical gadgets.

Hinge joint Allows the bones to move only backand forth, not side to side (as in adoor hinge).

Examples: knee and smaller knuckles of fingers.

Ball-and-socket joint Allows the bones to move back andforth, side to side, and sometimesrotate.

Examples: hips, shoulders, largestknuckles.

Saddle joints Shaped like a saddle for tilting and sliding.

Example: thumb.

Washer joints Limited tilting with a pad or washerof cartilage between the bone ends.

Examples: joints between thebackbones, where the cartilage padis called the intervertebral disc.

Fixed or suture joint No movement at all, because thebones are firmly joined together.

Examples: between the bones of thecranium (upper skull) around the brain.

PARTS OF A BONEBONES & JOINTS

• The word skeleton comes from anancient word meaning dried up. Butliving bones are not dry, they areabout one-quarter water. (Overall,the body is two-thirds water.)

• The main minerals in bone arecalcium, phosphate, and

carbonate. These form tiny crystalswhich give bone its hardness andstiffness.

• Bone also contains tiny fibers ofthe substance collagen, whichmakes it slightly flexible underpressure, and less likely to snap.

• If a bone is soaked in a specialacid chemical, the crystals ofcalcium phosphate and calciumcarbonate are removed. Only thecollagen fiber are left. This meansthat it is so flexible that a longbone like the upper-arm bone canbe tied in a knot.

BONE RECORDS

Your skeleton holds you up, but you would not be able to move if it

was not for the joints that link your bones together. More than half of

your body’s bones—112 out of 206—are in your wrists, hands,

fingers, ankles, feet, and toes. So are more than half of your 200-plus joints.

Your bones, muscles and joints work so closely together that they are

sometimes viewed as a single system, called the musculoskeletal system.

The two topmost backbones(cervical vertebrae), justunder the skull, have specialjoint designs. They allow thehead to make importantmovements.

• The axis (uppermost) backbonehas a curved shape like a saddle.It allows the head to tilt to theside and nod.

• The atlas (second uppermost)backbone is more like a ring andallows the head to turn or rotateto look to the side.

• Where the ends of a bone touchin a joint, they are covered withsmooth, glossy cartilage, toreduce wear and rubbing.

• The space between the bones isfilled with a slippery liquid calledsynovial fluid, thatreduceswear evenmore.

• The fluid is kept in by a loose bagaround the joint, the joint capsule.

• New synovial fluid is alwaysbeing made by

the inner lining of this bag, calledthe synovial membrane.

REDUCING WEAR AND TEAR

Joints allow the skeleton to move. They can be found

all over the body.

WHERE IN THE BODY? Longest

The thigh bone (femur), formingabout one-quarter of total bodyheight.

WidestThe hip bone (pelvis), forming thebody’s broadest part.

SmallestThe stirrup (stapes) deep inside theear, a U shape just .031 in. long.

ToughestThe lower jaw (mandible), usedhundreds of times daily when

Nodding and shaking yourhead is only possible with

two special joint designs inthe backbone.

HeadThe rounded end of

a long bone.

TubercleA lumpy projection on abone, usually where a

muscle is attached.

ShaftThe slimmer middlepart of a long bone.

PeriosteumThe outer covering wrapped allaround the bone.

ForamenSmall hole in a bone, where a nerveor blood vessel passes inside.

Compact boneVery strong, hard outer layer ofbone, like a shell.

Osteons (Haversian systems)Tiny cells of bone substance bundledand glued together to makecompact bone.

Spongy or cancellous boneInner layer of a bone, under thecompact bone, that has holes like a sponge.

MarrowJelly-like substance in the center of most bones.

Red marrowFound in all bones of a baby, butonly in the long bones of the armsand legs, ribs, backbone,breastbone and upper skull in anadult. Makes new microscopic cellsfor the blood.

Yellow marrowIn adults, found mainly in smallerbones of the hands and feet.Contains fat for use as an energyreserve, but can change to redmarrow if needed.

Bones are held together at a joint by stretchy straps calledligaments, which stop themmoving too far or coming apart. If the bones slip and come out oftheir usual position, a dislocationoccurs.

Ligament Muscle

During long space flights, the lackof gravity puts bones under lesspreasure than they are on Earth.The bones start to lose mineralsand become weaker. Astronautsexercise regularly to keep their

bones strong.

Even a large joint like the hipcontains only about a teaspoonof synovial fluid.

PARTS OF A BONE

LIGAMENTS YES AND NO

BONE MAKE UP

Your single biggest joint, the knee, has an unusual design with extra cartilages and ligaments.

• In addition to the cartilage covering theends of the thigh and shin bones, the cartilage covers the knee withtwo pieces of moon-shapedcartilage.

• The cartilage pieces are calledmenisci and help the knee tolock straight so you can standup easily.

• When atheletes have tornknee cartilage, it’s usually oneof these menisci which isdamaged.

• The knee has two strong sets of ligaments, the lateral

ligaments on the outer side andthe medial ligaments on the

inner side (next to the other knee).

• As well as these, it hastwo ligaments inside, keeping

the ends of the bones very closetogether.

• These two ligaments form an X-like shape and are called

cruciate ligaments.

Exercising and playing sportscan sometimes damage

your knee. It isimportant to always

warm up.• See pages12–13 for information

on muscles.

• See pages 40–41 FOOD AND NUTRIENTS

There are eight bones in thecranium. They are fused togetherto protect the brain underneath.

BIGGEST JOINT

THE NERVOUS SYSTEMThe nervous system controls every movement and action we make, as

well as every process that happens inside the body. Your nervous

system is made up of your brain, spinal cord, and nerves. It works by

sending tiny electrical signals, called nerve impulses. Millions of these travel

around the body and brain every second.

A nerve signal is a tiny pulse of electricity made by movingchemical substances into and out of the nerve cell.

• Average signal strength is 1⁄10 th of a volt.

• Average signal length is 1⁄1000th of a second.

• Average recovery time before another signal can pass is 1⁄500 th of a second.

• Slowest signals travel 19 inches per second.

• Fastest signals travel 459 feet per second.

NERVE SIGNALS• Some parts of the nerve system

work automatically.

• Those processes are called theautonomic nerve system.

• They control heartbeat, fooddigestion, body temperature,and blood pressure.

AUTOMATIC SYSTEM

There are two mainnervous systems within thebody. The central nervoussystem is the brain’s maincontrol center. It sendsnerve impulses to the restof the body using theperipheral nervous system.We have conscious controlover the central andperipheral nervous systems.

Central nervous system:BrainInside the top half of the head.Spinal cordThe main nerve link between the brain and the body.

Peripheral nervous system:Cranial nervesConnect directly to the brainrather than the spinal cord. They go mainly to parts in thehead like the eyes, ears, andnose.Spinal nervesBranch out from the spinal cordto the arms, legs, back, chest,and all other body parts.

MAIN PARTS OF THENERVOUS SYSTEM

The sciatic nerve, in the hip and upperthigh, is about thewidth of its owner’sthumb. This is thickerthan the spinal cord,which is usually thewidth of its owner’slittle finger.

Nerves run throughout the body,carrying electrical signals

from the brain.

WHERE IN THE BODY?

We have no conscious controlover some parts of our body,such as the systems thatcontrol digestion.

NERVES AND NERVE CELLS

axons

A nerve’s outer covering is called theepineurium. Inside are bundles of nerve fibers, called axons,each too small to see without a microscope.

SLOW TO HURTWhen you hurt a finger, youprobably feel the touch first, andthen the pain starts a moment later.This is because the signals abouttouch travel faster along the nervesthan the signals about pain.

18

• See pages 20–21 forinformation on THE BRAIN.


THICKEST NERVE

epineurium

12 pairs of cranial nervesjoin directly to the brain and link it to the followingparts:

1. Nose For smelling

2. Eyes For seeing

3. Eyeball-moving muscles


5. Skin and touch On forehead, face, cheeks, jaw muscles, muscles for chewing


7. Tongue For taste, saliva glands, tear glands, facial expressions

8. Ear For hearing and balance

9. Rear of tongue For taste, swallowing muscles

10. Swallowing musclesAlso lungs and heart in chest

11. Voicebox muscles For speaking

12. Tongue muscles For speaking and swallowing

D I R E C T T O T H EB R A I NNerves are flexible but tough, so they can move easily at joints but

withstand being squeezed by the muscles around them.

• Each nerve fiber is the long, wire-like part of a single microscopicnerve cell, called a neuron.

• Usually near one end, the nervecell has a wider part, called thecell body.

• Branching from the nerve cell body are even thinnerspidery-looking parts, calleddendrites.

• Nerve messages from other nerve cells are picked up by the dendrites, processed andaltered as they pass around the cell body, and then sent by the axon (fiber) to other nerve cells.

• Most nerve fibers are 0.0003 in.wide, so 4000 side by sidewould be just over 1 inch.

• They have a covering wrappedaround them, called the myelinsheath. It makes nerve messagestravel faster and stops themleaking away.

• Joins the brain to the mainbody.

• Is about 17 in. long in a typicaladult.

• Has 31 pairs of nerves branchingleft and right from it.

• Is protected inside a “tunnel”formed by a row of holes throughthe backbones.

• Like the brain, it has a layer of liquid around it, calledcerebrospinal fluid, to cushion itfrom injury.

NERVE LENGTHS• All the nerves in the body,

taken out and joined end to end, would stretch about 62 miles.

• The longest single nerve fibers,found in the legs, are up to 3feet in length.

The spinal cord, in the back, is one of the most important partsof our nervous system.

Each nerve cell receivessignals from thousands ofother cells and passes onsignals to thousands more.

• Individual nerve cells do notactually touch each other wherethe ends of their dendrites andaxons come together.

• The ends are separated by tinygaps, at junction points, calledsynapses.

• The gap inside a synapse is just1 microinch wide, which means1 million in a row would stretch1 inch.

• Nerve messages jump across asynapse not as electrical signals,but in the form of chemicals,called neurotransmitters.

• This chemical “jump” takes lessthan 1⁄1,000th of a second.

A typical nerve looks likewire or string.

Synapses are so small thatscientists have to use special

electron microscopes to study them.

Nerves are connected toevery body part.

• The thickest ones near the brainand spinal cord are known asnerve trunks.

• The thinnest ones spreading intobody parts are called terminalfibers.

NERVEST O E V E R Y P A R T

19

THE NERVOUS SYSTEMThe nervous system controls every movement and action we make, as

well as every process that happens inside the body. Your nervous

system is made up of your brain, spinal cord, and nerves. It works by

sending tiny electrical signals, called nerve impulses. Millions of these travel

around the body and brain every second.

A nerve signal is a tiny pulse of electricity made by movingchemical substances into and out of the nerve cell.

• Average signal strength is 1⁄10 th of a volt.

• Average signal length is 1⁄1000th of a second.

• Average recovery time before another signal can pass is 1⁄500 th of a second.

• Slowest signals travel 19 inches per second.

• Fastest signals travel 459 feet per second.

NERVE SIGNALS• Some parts of the nerve system

work automatically.

• Those processes are called theautonomic nerve system.

• They control heartbeat, fooddigestion, body temperature,and blood pressure.

AUTOMATIC SYSTEM

There are two mainnervous systems within thebody. The central nervoussystem is the brain’s maincontrol center. It sendsnerve impulses to the restof the body using theperipheral nervous system.We have conscious controlover the central andperipheral nervous systems.

Central nervous system:BrainInside the top half of the head.Spinal cordThe main nerve link between the brain and the body.

Peripheral nervous system:Cranial nervesConnect directly to the brainrather than the spinal cord. They go mainly to parts in thehead like the eyes, ears, andnose.Spinal nervesBranch out from the spinal cordto the arms, legs, back, chest,and all other body parts.

MAIN PARTS OF THENERVOUS SYSTEM

The sciatic nerve, in the hip and upperthigh, is about thewidth of its owner’sthumb. This is thickerthan the spinal cord,which is usually thewidth of its owner’slittle finger.

Nerves run throughout the body,carrying electrical signals

from the brain.

WHERE IN THE BODY?

We have no conscious controlover some parts of our body,such as the systems thatcontrol digestion.


axons

A nerve’s outer covering is called theepineurium. Inside are bundles of nerve fibers, called axons,each too small to see without a microscope.

SLOW TO HURTWhen you hurt a finger, youprobably feel the touch first, andthen the pain starts a moment later.This is because the signals abouttouch travel faster along the nervesthan the signals about pain.

18



THICKEST NERVE

epineurium

NERVE JUNCTIONS

SPINAL CORD


• See pages 50–51for information on the

STAGES OF LIFE.

20

• Bigger brains are not necessarilysmarter, and there is no linkbetween the size of a healthybrain and intelligence.

• The average female brain isslightly smaller than the averagemale brain.

• But the average female body issmaller, in comparison, to theaverage male body.

• Compared to body size, womenhave slightly larger brains than men.

SIZE ISN’T EVERYTHING

The brain contains more than 100 billion nerve cells, called neurons—

about as many stars as in our galaxy, the Milky Way. The brain also

contains perhaps ten times as many support cells, called neuroglia.

It’s not the size of a brain which makes it smart, or the number of cells. It

depends on how often its owner uses it, and in how much detail—by looking,

listening, learning, remembering, using imagination, and having ideas.

THE BRAIN

The brain is inside the cranium,forming the upper half of

the head.

WHERE IN THE BODY?

• The brain consumes about one-fifth of all the energy used bythe body.

• But the brain forms only about1⁄50 th of the whole body.

• That means the brain uses tentimes more energy for its size,compared to most other body parts.

• This energy is mainly in the form of blood sugar, calledglucose, brought to the brain byits main blood vessels, thecarotid and vertebral arteries.

• Average blood flow to the brainis 1.5 pints per minute, aboutone-eighth of the heart’s totaloutput.

• This flow is the same whetherthe body is at rest or very active.

• This is unusual because bloodflow to other body partschanges greatly between restand activity. For example, it increases to the muscle by ten times and decreases to thestomach by half.

HUNGRY FOR ENERGY

The weight of an averageadult brain is 3 pounds.

The largest accurately measured normal human brain is 6.3 pounds.

THE WEIGHT OFTHE BRAIN

planningmovement

making movement

hearing

speechtouch on the skin

vision

• The outer gray layer of thecerebrum, over the top of thebrain, is called the cerebral cortex.

• Spread out flat, it would be thearea of a pillowcase, and almost asthin.

• However, deep grooves, called sulci,are wrinkled and folded into thespace inside the upper skull.

• The cortex has about half thebrain’s total number of nerve cells,around 50 billion.

• Each of these can have connectionswith more than 200,000 othernerve cells.

• The connections are made by thespidery-looking arms, calleddendrites, and a much longer, wire-like part, the nerve fiber.

• The cortex is the main place wherewe become aware of what we see,hear, smell, taste, and touch..

• It is also the place where we plan movements and actions and get them started, known asmotor skills.

• Each of these sensory and motorprocesses takes place in a different area of the cortex,known as a center.

• The cortex is also the major site forthinking and consciousness, whatwe call our “mind”.

• The cortex is also involved inlearning and memory, althoughscientists are not quite sure how.

• See pages 34–35for information on the CIRCULATORY SYSTEM

• See pages 22–27 forinformation on the senses.

• See pages 12–13 forinformation on muscles.

CORTEX IN CONTROL

21

• Nerve messages from the bodycross over from left to right at thebase of the brain.

• This means the left side of the brainreceives signals from, and sendsthem to, the right side of the body.

• In most people, the left side of thebrain is more active in speakingand reading, scientific skills, usingnumbers and maths, and workingout problems in a logical way.

• The right side of the brain is more

active in dealing with shapes andcolors, artistic skills like paintingand music, and having creativeideas.

• In a right-handed person, the leftside of the brain is generallydominant. In a left-handed person,the right side of the brain isgenerally dominant.

Even when asleep, the brain is justas active sending nerve messagesaround itself as it is when awake.This is shown by recordings of itselectrical nerve signals.• Older people tend to sleep more

hours overall but often in severalshorter sessions, such as “cat-naps” through the day.

• Usual sleep needs for most peopleevery 24 hours:

New born 20 hours

10-year-old 10 hoursAdult 7–8 hours

SLEEP• The brain has four small chambers

inside it called ventricles.

• These are filled with a pale liquidcalled cerebrospinal fluid, CSF.

• CSF is found around the brain,between two of the protectivelayers, called meninges, thatsurround it. CSF is also found inand around the spinal cord.

• The total amount of CSF insideand around the brain and spinalcord is about 4.2 fl.oz.

• This fluid flows very slowly and isgradually renewed about threetimes every 24 hours.

• CSF is important as it helps tocushion the brain from damage.

• The liquid also supports the brainwithin the skull, bringsnourishment, and takes awaywastes.

HOLLOW BRAIN

CerebrumThe big wrinkled, domed partcovering most of the top of thebrain, forms more than four-fifths of the whole brain. It hasa thin outer layer of “graymatter,” the cerebral cortex,which is mainly nerve cells,covering an inner mass of“white matter,” which ismainly nerve fibers. Hypothalamus

Just below and in front of the thalamus,is a main center for

powerful feelings,emotions, and urgessuch as anger, fright,love, and joy.

ThalamusThis is two egg-shaped partsalmost at the center of thebrain. It helps to sort andprocess information fromfour of the senses (sight,hearing, taste, and touch)going to the cerebrumabove.

CerebellumA smaller wrinkled part at thelower back, looks like a smallerversion of the whole brain. infact its name means little brain.It carries out detailedcontrol of muscles sowe can move about,keep our balance, and carryout skilled actions.

The brain stem At the base of the brain contains the main life support areas for

heartbeat, breathing, blood pressure, and control of digestion. Its lowerend merges into the top of the spinal cord.

In a left-handed person, theright side of the brain is

generally dominant.

T H E G R O W I N GB R A I N

The development of thebrain happens quickly afterconception. It continues togrow in size after birthand makes new nerveconnections throughoutchildhood.

Inside the womb• The brain is one of the first

main body parts to form just

three weeks after conception

as a large arched bulge at the

head end.

Four weeks after conception• The brain is almost larger than

the rest of the body.

20 weeks after conception• Brain weighs about 3.5 oz.

At birth• The brain is 14–17 oz., about

one-third of its final adult size.

In comparison, a new baby’s

body is about 1/25th

of its final adult size.

Growing up• By 3 years, the brain is

approaching fully grown at

2.4 lbs.

• The brain does not make any

new nerve cells after birth.

• The brain does make new

connections between nerve cells,

perhaps millions every week, as

we take in knowledge, develop

skills and learn new things.

From 20 years old onward• The brain shrinks by about 0.03

oz. of weight per year. This

represents the loss of around

10,000 nerve cells each day.

• Certain drugs, including alcohol,

can speed this cell loss and make

the brain shrink faster.

• See pages 50–51for information on the

STAGES OF LIFE.

20

• Bigger brains are not necessarilysmarter, and there is no linkbetween the size of a healthybrain and intelligence.

• The average female brain isslightly smaller than the averagemale brain.

• But the average female body issmaller, in comparison, to theaverage male body.

• Compared to body size, womenhave slightly larger brains than men.

SIZE ISN’T EVERYTHING

The brain contains more than 100 billion nerve cells, called neurons—

about as many stars as in our galaxy, the Milky Way. The brain also

contains perhaps ten times as many support cells, called neuroglia.

It’s not the size of a brain which makes it smart, or the number of cells. It

depends on how often its owner uses it, and in how much detail—by looking,

listening, learning, remembering, using imagination, and having ideas.

THE BRAIN

The brain is inside the cranium,forming the upper half of

the head.

WHERE IN THE BODY?

• The brain consumes about one-fifth of all the energy used bythe body.

• But the brain forms only about1⁄50 th of the whole body.

• That means the brain uses tentimes more energy for its size,compared to most other body parts.

• This energy is mainly in the form of blood sugar, calledglucose, brought to the brain byits main blood vessels, thecarotid and vertebral arteries.

• Average blood flow to the brainis 1.5 pints per minute, aboutone-eighth of the heart’s totaloutput.

• This flow is the same whetherthe body is at rest or very active.

• This is unusual because bloodflow to other body partschanges greatly between restand activity. For example, it increases to the muscle by ten times and decreases to thestomach by half.

HUNGRY FOR ENERGY

The weight of an averageadult brain is 3 pounds.

The largest accurately measured normal human brain is 6.3 pounds.

THE WEIGHT OFTHE BRAIN

planningmovement

making movement

hearing

speechtouch on the skin

vision

• The outer gray layer of thecerebrum, over the top of thebrain, is called the cerebral cortex.

• Spread out flat, it would be thearea of a pillowcase, and almost asthin.

• However, deep grooves, called sulci,are wrinkled and folded into thespace inside the upper skull.

• The cortex has about half thebrain’s total number of nerve cells,around 50 billion.

• Each of these can have connectionswith more than 200,000 othernerve cells.

• The connections are made by thespidery-looking arms, calleddendrites, and a much longer, wire-like part, the nerve fiber.

• The cortex is the main place wherewe become aware of what we see,hear, smell, taste, and touch..

• It is also the place where we plan movements and actions and get them started, known asmotor skills.

• Each of these sensory and motorprocesses takes place in a different area of the cortex,known as a center.

• The cortex is also the major site forthinking and consciousness, whatwe call our “mind”.

• The cortex is also involved inlearning and memory, althoughscientists are not quite sure how.

• See pages 34–35for information on the CIRCULATORY SYSTEM

• See pages 22–27 forinformation on the senses.


CORTEX IN CONTROL

MAIN BRAIN PARTS

LEFT AND RIGHT

• See pages12–13 for information

on muscles.

22

• The eye’s inner lining, the retina,is where light rays are changed tonerve signals.

• The retina has an area about thesame as a larger postage stamp.

• It has millions of microscopic cellsthat make nerve signals when hitby light rays.

• 125 million are rod cells, whichwork well in dim light, butcannot see colors, only shades ofgray.

• 7 million are cone cells, whichsee fine details and colors, butwork only in bright light.

• Most of the cones areconcentrated in a slightly bowl-shaped hollow at the back of the

retina, the fovea, or yellow spot.

• This is where light falls to give usthe clearest, most detailed view.

Experts believe that over half of the information we process comes in

through our eyes, as words (through reading), pictures, drawings,

real-life scenes, and images on screens. Yet the eye does not really

see. It turns patterns of light rays into patterns of nerve signals, which go to

the brain. The visual center at the back of the brain is the “mind’s eye,”

where we recognize and understand what we see.

EYES AND SIGHT

Each eyeball is in a bony bowl called the eye socket.It is formed by curved parts

of five skull bones.

WHERE IN THE BODY?

• Some people see spots or “floaters”that seem to be in front of the eye.

• These are actually in the vitreoushumor jelly filling the inside of theeyeball.

• They are usually stray red bloodcells or bits of fibers that haveescaped from the retina.

• We can’t look straight at thembecause as we move the eyeball,they move also.

• A few floaters are normal, butmedical help is needed if theysuddenly increase in number.

FLOATERS

The place where all the retina’snerve fibers come together toform the start of the optic nerveis called the optic disc.• Since light cannot be detected

here, it is known as the blind spot.• Normally, we don’t notice the

blind spot because our eyescontinually dart and look aroundat different parts of a scene.

• As we do this the brain guessesand “fills in” the missing areafrom what is around and what ithas seen just before or after.

• The optic nerve contains onemillion nerve fibers—the most of any nerve carrying senseinformation to the brain.

BLIND SPOT

As it goes dark in the evening, what we see seems to lose color. This is because the cone cells work less,and we rely on the rods.

Many people who are red-greencolor blind can learn to tell colorsapart by their shade or huerather than the actual color.

• There are three kinds of light-detecting cone cells in the retina.

• They are called red, green, andblue cones.

• This is not because of their colors;they all look the same.

• The three types of cones detectthree different colors of light.

• The brain works out the color ofan object from the active cones.

• In some people, not all thesecones are present or workproperly.

• This is called color blindness,or color vision deficiency.

• Most common is when red andgreen are not seen very differently.

• This often runs in families andaffects more males than females.

• True color blindness, seeingeverything in shades of gray (like a black-and-white movie), isvery rare, affecting less than 1 in10,000 people.

• See pages 18–19 forinformation on the nerves.

WHAT AN INCREDIBLE SIGHT

COLOR CONES

The saying 20/20 vision came about from the way of describing how clearly a person can see.

23

M O V I N G T H E EYEBALLBehind the eyeball are six small ribbon-shapedmuscles that make it turnand swivel in its socket or eye orbit.

Medial rectus

Moves the eye inward, toward the nose.

Lateral rectus

Moves the eye outward, away from the nose.

Superior rectus

Moves the eye upward, to look at the sky.

Inferior rectus

Moves the eye downward, to lookat the floor.

Superior oblique

Pulls eye inwards and downwards.

Inferior oblique

Pulls eye upwards and outwards.

In total the eye can tilt as follows:

• look up by 35 degrees.

• look down by 50 degrees.

• look inward towards the noseby 50 degrees.

• look outward by 45 degrees.

• Every person in the world hasdifferent fingerprints, which canbe used for identification andsecurity checks.

• The same applies to the colouredpart of the eye, the iris.

• Each person has a different colorand detailed pattern of marks onthe iris.

• Scans of the iris, fed into acomputer, can be used likefingerprints for identification andsecurity checks.

• Rarely does a person have twodifferent colored irises, though itcould happen at birth, or throughinjury.

• 20/20 means a person can see,at a distance of 20 feet, whatnormal eyesight can show.

• The larger the second number, theworse the eyesight.

• Someone with 20/60 vision cansee at 20 feet what normaleyesight sees clearly at 60 feet.

• Nearsightedness, or myopia, isdue to the eyeball being toolong form front to back.

• Farsightedness, or hypermetropia,is due to the eyeball being tooshort from front to back.

• Astigmatism is when the curve ofthe eyeball is not the same in alldirections.

• We spend about up to 30 minutes ofour waking day with our eyes shutduring blinks.

• Blinking washes soothing, cleansingtear fluid over the eye. The fluidwashes away dust and helps to kill germs.

• Tear fluid comes from the lacrimalgland, just above and to the outerside of each eye, under a fold of skin.

• On average:Number of blinks per minute: 6Length of blink: 0.3-0.4 secondsTotal amount of tear

fluid made in a day: 50 ml

This can treble if surroundings are dustyor have chemical fumes.

BLINKING AMAZING

20/20 VISION

MAIN PARTS OF THE EYE

M E A S U R I N GTHE EYE

The eyeball is almost aperfect sphere or ballshape.

Side-to-side: 0.94 in.

Front-to-back: 0.94 in.

Top-to-bottom: 0.91 in.

• The eyeball’s total weight is0.8–1 oz.

• The eye is one of the bodyparts that grows least frombirth to adulthood.

PupilHole in the iris, through whichlight enters the eye’s interior.

IrisColored ring of muscle that can alter thesize of the hole within it, the pupil,making it smaller in bright light toprotect the delicate inside of the eye.

ScleraTough outer layer around the wholeeye apart from the cornea.

Cornea Thick clear dome at the front of the eye.

ConjunctivaSensitive covering at the front of theeyeball, over the cornea.

LensPea-shaped blob about 0.4 in. acrossthat alters in shape to see and focusclearly, from looking at farawayobjects to nearby ones.

RetinaInner layer lining the eyeball’s interior.

ChoroidBlood-rich layer between sclera and retina.

Ciliary muscle Ring of muscle around the lens thatalters its shape.

Aqueous humor Thin, clear fluid filling the spacebetween the cornea and the lens.

Vitreous humor Thick, clear jelly-like substance fillingthe main eyeball and giving itsrounded shape.

Usually, people with darkerskin and hair have browneririses. People with lighter skinand hair have bluer irises.


on muscles.

22

• The eye’s inner lining, the retina,is where light rays are changed tonerve signals.

• The retina has an area about thesame as a larger postage stamp.

• It has millions of microscopic cellsthat make nerve signals when hitby light rays.

• 125 million are rod cells, whichwork well in dim light, butcannot see colors, only shades ofgray.

• 7 million are cone cells, whichsee fine details and colors, butwork only in bright light.

• Most of the cones areconcentrated in a slightly bowl-shaped hollow at the back of the

retina, the fovea, or yellow spot.

• This is where light falls to give usthe clearest, most detailed view.

Experts believe that over half of the information we process comes in

through our eyes, as words (through reading), pictures, drawings,

real-life scenes, and images on screens. Yet the eye does not really

see. It turns patterns of light rays into patterns of nerve signals, which go to

the brain. The visual center at the back of the brain is the “mind’s eye,”

where we recognize and understand what we see.

EYES AND SIGHT

Each eyeball is in a bony bowl called the eye socket.It is formed by curved parts

of five skull bones.

WHERE IN THE BODY?

• Some people see spots or “floaters”that seem to be in front of the eye.

• These are actually in the vitreoushumor jelly filling the inside of theeyeball.

• They are usually stray red bloodcells or bits of fibers that haveescaped from the retina.

• We can’t look straight at thembecause as we move the eyeball,they move also.

• A few floaters are normal, butmedical help is needed if theysuddenly increase in number.

FLOATERS

The place where all the retina’snerve fibers come together toform the start of the optic nerveis called the optic disc.• Since light cannot be detected

here, it is known as the blind spot.• Normally, we don’t notice the

blind spot because our eyescontinually dart and look aroundat different parts of a scene.

• As we do this the brain guessesand “fills in” the missing areafrom what is around and what ithas seen just before or after.

• The optic nerve contains onemillion nerve fibers—the most of any nerve carrying senseinformation to the brain.

BLIND SPOT

As it goes dark in the evening, what we see seems to lose color. This is because the cone cells work less,and we rely on the rods.

Many people who are red-greencolor blind can learn to tell colorsapart by their shade or huerather than the actual color.

• There are three kinds of light-detecting cone cells in the retina.

• They are called red, green, andblue cones.

• This is not because of their colors;they all look the same.

• The three types of cones detectthree different colors of light.

• The brain works out the color ofan object from the active cones.

• In some people, not all thesecones are present or workproperly.

• This is called color blindness,or color vision deficiency.

• Most common is when red andgreen are not seen very differently.

• This often runs in families andaffects more males than females.

• True color blindness, seeingeverything in shades of gray (like a black-and-white movie), isvery rare, affecting less than 1 in10,000 people.

• See pages 18–19 forinformation on the nerves.

IRIS SECURITY SCANS

WHAT AN INCREDIBLE SIGHT

COLOR CONES

The saying 20/20 vision came about from the way of describing how clearly a person can see.

24

• Three semicircular canals in the earare at right angles to each other.

• Each canal has a jelly-like blob at oneend in its ampulla or widened part.

• There are microhairs in the jelly-like blob.

• As the head moves, fluid in thecanal swishes and moves the jelly-like blob.

• This moves the hairs of the haircells, which make nerve signalsand send them to the brain.

• The wider parts next to the canals,the utricle and saccule chambers,have more blobs with hairs in them.

• Gravity pulls these down, bendingthe hairs and making the hair cellsproduce nerve signals.

• The canals sense headmovements while the chambersdetect head position.

• But balance involves much more,including information from theeyes about what is upright andlevel, from the skin about whetherthe body is leaning, and frominside the muscles and jointsabout strains on them.

• The brain uses all this informationto adjust muscles and keep uswell-balanced.

THE SENSE OF BALANCE

• The body’s six smallest bones,three in each middle ear.

• They were named long agofrom items more common atthe time, to do withhorseriding and ironsmiths.

• Hammer (malleus) isattached to the eardrum.

• Anvil (incus) is the middle ofthe three.

• Stirrup (stapes) is attachedto the oval window of thecochlea.

We can usually hear some kind of sound, whether it be the roar of a

jet plane, friends talking, birds singing, or the wind rustling

grass. Most of the time, we are not aware of sounds around us,

because they tell us nothing new. The brain blocks out frequent noise like

humming machinery or distant traffic. Only when we hear something new,

important, or exciting, does the mind turn its attention to hearing.

EARS AND HEARING

EAR BONESThe outer ear is on the side ofthe head, usually level with

the nose. The inner ear is deepin the temporal skull bone,

almost behind the eye.

WHERE IN THE BODY?

• Sound travels about 0.2 mi. persecond in air.

• A sound from one side reachesthe ear on that side more than1,000th of a second before itreaches the other ear.

• The sound is louder and clearer in the closer ear, too.

• The brain can detect thesedifferences in time, volume, andclarity, and work out the directiona sound comes from.

• This is known as stereophonichearing.

• Headphones and earphonescopy these differences to givethe impression of directionalsounds.

• Even sounds in front and behindcan be told apart, whether they come from below or above.

• A sound from the floor directlyin front causes some echoes andbrings these mixed in with it.

• A sound from directly above hasfewer echoes and reach the earsafter the main sound.

STEREO HEARING

The ear is divided into threemain sections:Outer earEar flap (pinna or auricle) and earcanalMiddle ear Eardrum, tiny ear bones, andmiddle ear chamberInner ear Cochlea, semi-circular canals, andtheir chambers

OUTSIDE TO INSIDE

In space, there is no gravity to help give astronauts a sense of balance. The lack of gravity causes some people to

develop motion sickness.

• See pages 14–17 forinformation on bones.


25

L O U D N E S S O FSOUNDSSound intensity (roughlythe same as loudness orvolume) is measured inunits called decibels, dB.

0 dB Total silence

10 dB Limit of human hearing

20 dB Watch ticking

30 dB Whisper

40 dB Quiet talking, distant traffic

50 dB Normal talking

60 dB Normal television volume

70 dB Traffic on city street,vacuum cleaner

80 dB Alarm clock ringing,nearby truck

90 dB Heavy traffic on highway,music at a concert

100 dB Chainsaw, construction drill

Eardrum surface area 0.085 sq in. (about the size of the nail on the little finger).

Stirrup bone less than 0.2 in. long.

Cochlea spiral like a snail, with two 27° turns.

Cochlea 0.35 in. across at the wide end.

Cochlea straightened out would stretch 1.4 in.

Semicircular canals each0.6–0.78 in. long, curved into a C-shape.(for balance)

Semicircular canals each less than 0.04 in. wide.

1 Sound waves approach asinvisible ripples of high and low air pressure.

2 Outer ear flap funnels soundwaves.

3 Ear canal carries them into the skull.

4 Eardrum vibrates as sound wavesbounce off it.

5 Vibrations pass along row ofthree tiny bones, called ossicles.

6 Third ossicle makes the thin“window” of cochlea vibrate.

7 Vibrations pass into fluid insidecochlea, causing ripples.

8 Ripples shake 50–100microhairs on each of 25,000microscopic hair cells inside cochlea.

9 Hair cells make nerve signalswhen shaken.

10 Nerve signals pass along nervefibers into the cochlear nerve.

11 Cochlear nerve is joined byvestibular nerve from balanceparts.

12 Both nerves form the auditory nervethat carries nerve signals to brain.

Sound reaches us as wavesof vibrations of the air.Higher sounds make the air vibrate more quicklythan lower sounds.

• Pitch is the scale of a sound—whether it makes the airvibrate at a high or lowfrequency.

• Our ears can detect soundsfrom 25 to 20,000 vibrationsper second.

• Dogs can detect much lowerand higher sounds than humanbeings.

PITCH

HOW WE HEAR

D A M A G ECONTROLSome sounds are too loudfor us to hear comfortably.We put our hands over our ears to try to protectour ears.• Sounds above 90 dB, especially

if high-pitched, can damagehearing.

• Many places have lawscontrolling noise, like factories,airports and music clubs.

ear bones

eardrum

cochlea

tensor tympanicmuscle

The ear canal leads from theouter ear to the eardrum.

It is 0.78 in. long and slightly S-shaped.

24

• Three semicircular canals in the earare at right angles to each other.

• Each canal has a jelly-like blob at oneend in its ampulla or widened part.

• There are microhairs in the jelly-like blob.

• As the head moves, fluid in thecanal swishes and moves the jelly-like blob.

• This moves the hairs of the haircells, which make nerve signalsand send them to the brain.

• The wider parts next to the canals,the utricle and saccule chambers,have more blobs with hairs in them.

• Gravity pulls these down, bendingthe hairs and making the hair cellsproduce nerve signals.

• The canals sense headmovements while the chambersdetect head position.

• But balance involves much more,including information from theeyes about what is upright andlevel, from the skin about whetherthe body is leaning, and frominside the muscles and jointsabout strains on them.

• The brain uses all this informationto adjust muscles and keep uswell-balanced.

THE SENSE OF BALANCE

• The body’s six smallest bones,three in each middle ear.

• They were named long agofrom items more common atthe time, to do withhorseriding and ironsmiths.

• Hammer (malleus) isattached to the eardrum.

• Anvil (incus) is the middle ofthe three.

• Stirrup (stapes) is attachedto the oval window of thecochlea.

We can usually hear some kind of sound, whether it be the roar of a

jet plane, friends talking, birds singing, or the wind rustling

grass. Most of the time, we are not aware of sounds around us,

because they tell us nothing new. The brain blocks out frequent noise like

humming machinery or distant traffic. Only when we hear something new,

important, or exciting, does the mind turn its attention to hearing.

EARS AND HEARING

EAR BONESThe outer ear is on the side ofthe head, usually level with

the nose. The inner ear is deepin the temporal skull bone,

almost behind the eye.

WHERE IN THE BODY?

• Sound travels about 0.2 mi. persecond in air.

• A sound from one side reachesthe ear on that side more than1,000th of a second before itreaches the other ear.

• The sound is louder and clearer in the closer ear, too.

• The brain can detect thesedifferences in time, volume, andclarity, and work out the directiona sound comes from.

• This is known as stereophonichearing.

• Headphones and earphonescopy these differences to givethe impression of directionalsounds.

• Even sounds in front and behindcan be told apart, whether they come from below or above.

• A sound from the floor directlyin front causes some echoes andbrings these mixed in with it.

• A sound from directly above hasfewer echoes and reach the earsafter the main sound.

STEREO HEARING

The ear is divided into threemain sections:Outer earEar flap (pinna or auricle) and earcanalMiddle ear Eardrum, tiny ear bones, andmiddle ear chamberInner ear Cochlea, semi-circular canals, andtheir chambers

OUTSIDE TO INSIDE

In space, there is no gravity to help give astronauts a sense of balance. The lack of gravity causes some people to

develop motion sickness.

• See pages 14–17 forinformation on bones.


EAR MEASUREMENTS

TWISTERUsually we don’t have tothink about talking. Thewords just come out of our mouth.

When we try to say a tonguetwister, we realize how difficult it can be for the brain and thetongue to work together. Try these!

• Which wristwatches are Swisswristwatches?

• A skunk sat on a stump and thunkthe stump stunk, but the stumpthunk the skunk stunk.

26

• The olfactory patch in the top of the nasal chamber is aboutthe size of a thumbnail.

• Each olfactory patch has 10 million smell hair cells.

• Each smell hair cell has 10–20micro-hairs sticking down from it.

• All the micro-hairs from onenose, joined end to end, wouldstretch over 109 yards.

• The micro-hairs stick into thesticky slimy mucus that lines the inside of the nasal chamber,inside the nose.

• Odorant particles floating in air seep into the slimy mucuscoating the inside of the nasalchamber.

• They then come into contact with the micro-hairs.

• A single smell hair cell lives for about 30 days and is thenreplaced.

• Over many years, some smellhair cells die but are notreplaced. Younger people have a more sensitive sense of smellthan older people.

Experts are still not exactlysure how smell and tastework. The main idea is thelock and key theory.

• Microscopic sense cellsfor both smell andtaste are called haircells, and have manytiny hairs stickingout, known as cilia.

• These hairs are coated withthousands ofdifferent-shapedreceptors, or“landing pads”.

• Each type of smell or flavor particlehas its own particular shape.

• Particles try to fit in all thereceptors on the hairs, but only

fit into certain receptorsof the same shape,like a key fitting into alock.

• When a particle fits into a receptor,

the hair cell sends a nerve signal to the brain.

• The brain works outthe smell or taste from the overall pattern of nerve signals it receives.

Smell and taste are called chemosenses. This means the nose and tounge

detect chemical substances—tiny particles too small to see. The nose

reacts to particles called odorants floating in the air. The tongue

detects particles called flavorants in foods and drinks. Both these senses are

very useful, since they can warn us of danger, but they also give us plenty

of pleasure.

NOSE AND TONGUE

LOCK AND KEYThe nasal and oral chambers—

nose and mouth—form thefront lower quarter of the head,

each shaped by the skull andjaw bones around it.

WHERE IN THE BODY?

Nerve signals about smelltake a different routethrough the brain, comparedto signals from other senses.They pass through the part of braincalled the limbic system, that isinvolved in feelings and emotions.This is why a strong smell bringsback powerful memories andfeelings.

FAST TRACK SIGNALS

NostrilsTwo holes, each leading to one sideof the nasal chamber.

Nasal cartilagesCurved sheets of cartilage formingthe sticking-out part of the nose.

Nasal chamber The air space inside the nose,roughly below the inner sides of theeyes.

SeptumFlat sheet of cartilage dividing thetwo halves of the nasal chamber.

Turbinates Shelf-like ridges on each outer sideof the nasal chamber.

Olfactory patch Fuzzy-looking area inside the top of each half of the nasal chamberthat detects smells.

INSIDE THE NOSE

nasal cavity

olfactory (smell nerves)

teeth

lips

tongue


A rose produces aparticular smellparticle that our

nose can recognize.

MICRO-DETAILS: THE NOSE

27

T O N G U ET A S K SThe tongue is the body’smost flexible muscle.

It has twelve parts of musclesinside it, and it goes from longand thin, poking out, to short andwide at the back of the mouth, inless than a second.

In addition to taste, the tongue:

Helps in eating• Moves food around inside the

mouth to chew it well.

• Separates a smaller lump of foodfrom the whole chewed mouthful,for swallowing.

• Cleans food off the teeth and lips.

Touches the lips• Moistening the lips helps them

seal together well.

• Stopping drool.

Communicates• Changes shape while speaking

to make words sound clear.

• Helps to make other sounds forcommunication, like whistles,hisses, and clicks.

When we taste a meal, it isnot only taste at work.

• Smells from food in the mouthfloat up, around the back of theroof of the mouth, into the nose.

• Here they are sensed by the nosein the usual way.

• Touch sensors in the gums and

cheeks and on the tongue tell us

about the food, too.

• These touch sensors detect if the

food is hot or cold, hard or soft,

or rough or smooth.

• Enjoying a meal involves taste,

smell, and touch.

• Most taste buds are around andbetween the little lumps on thetongue, called papillae.

• Each taste bud is shaped like a tinyonion and contains about 25 tastereceptor cells.

• Each taste receptor smell has about10 short microhairs sticking upfrom it.

• The microhairs stick through a holecalled a taste pore, at the top ofthe taste bud, onto the tongue’ssurface.

• Flavorant particles in foods anddrinks seep into the saliva covering

the tongue and come into contactwith the microhairs.

• A single taste receptor cell lives forabout 10 days and is thenreplaced.

• Over many years, some tastereceptor cells die but are notreplaced. So younger people havemore sensitive taste than olderpeople.

NOT ALL IT SEEMS

With practice, most peoplecould probably tell apart up to 10,000 different smells,odors, scents, and fragrances.

However, this depends on having a good memory as well as asensitive nose.

The nasal chamber inside the nosemakes up to one litre of slimymucus every day. Most we sniff inand swallow, some we blow out.

SNIFF SNIFF

We sense four differentbasic flavors on thetongue, sweet, salty,sour, and bitter.

• While there may be largergroupings of certain tastebuds, we can taste all favorsall over the tongue. The“tongue map” (on right)was disproved in 1974.

• There are no taste buds onthe main middle part of thetongue’s upper surface orunderneath the tongue.

bitter

soursour

salty salty

sweet

The tip, sides, and rear of thetongue have about 10,000 tinytaste buds, too small to see.

A close up view of a taste bud.

taste budpapillae

Food is less appetizing if wehave a cold. The nose is full of

mucus, hindering scent, andfood seems less “tasty.” In

fact, it is less “smelly.”

T O N G U ETWISTERUsually we don’t have tothink about talking. Thewords just come out of our mouth.

When we try to say a tonguetwister, we realize how difficult it can be for the brain and thetongue to work together. Try these!

• Which wristwatches are Swisswristwatches?

• A skunk sat on a stump and thunkthe stump stunk, but the stumpthunk the skunk stunk.

26

• The olfactory patch in the top of the nasal chamber is aboutthe size of a thumbnail.

• Each olfactory patch has 10 million smell hair cells.

• Each smell hair cell has 10–20micro-hairs sticking down from it.

• All the micro-hairs from onenose, joined end to end, wouldstretch over 109 yards.

• The micro-hairs stick into thesticky slimy mucus that lines the inside of the nasal chamber,inside the nose.

• Odorant particles floating in air seep into the slimy mucuscoating the inside of the nasalchamber.

• They then come into contact with the micro-hairs.

• A single smell hair cell lives for about 30 days and is thenreplaced.

• Over many years, some smellhair cells die but are notreplaced. Younger people have a more sensitive sense of smellthan older people.

Experts are still not exactlysure how smell and tastework. The main idea is thelock and key theory.

• Microscopic sense cellsfor both smell andtaste are called haircells, and have manytiny hairs stickingout, known as cilia.

• These hairs are coated withthousands ofdifferent-shapedreceptors, or“landing pads”.

• Each type of smell or flavor particlehas its own particular shape.

• Particles try to fit in all thereceptors on the hairs, but only

fit into certain receptorsof the same shape,like a key fitting into alock.

• When a particle fits into a receptor,

the hair cell sends a nerve signal to the brain.

• The brain works outthe smell or taste from the overall pattern of nerve signals it receives.

Smell and taste are called chemosenses. This means the nose and tounge

detect chemical substances—tiny particles too small to see. The nose

reacts to particles called odorants floating in the air. The tongue

detects particles called flavorants in foods and drinks. Both these senses are

very useful, since they can warn us of danger, but they also give us plenty

of pleasure.

NOSE AND TONGUE

LOCK AND KEYThe nasal and oral chambers—

nose and mouth—form thefront lower quarter of the head,

each shaped by the skull andjaw bones around it.

WHERE IN THE BODY?

Nerve signals about smelltake a different routethrough the brain, comparedto signals from other senses.They pass through the part of braincalled the limbic system, that isinvolved in feelings and emotions.This is why a strong smell bringsback powerful memories andfeelings.

FAST TRACK SIGNALS

NostrilsTwo holes, each leading to one sideof the nasal chamber.

Nasal cartilagesCurved sheets of cartilage formingthe sticking-out part of the nose.

Nasal chamber The air space inside the nose,roughly below the inner sides of theeyes.

SeptumFlat sheet of cartilage dividing thetwo halves of the nasal chamber.

Turbinates Shelf-like ridges on each outer sideof the nasal chamber.

Olfactory patch Fuzzy-looking area inside the top of each half of the nasal chamberthat detects smells.

INSIDE THE NOSE

nasal cavity

olfactory (smell nerves)

teeth

lips

tongue


HOW MANY? NOSE AND MEMORY

A rose produces aparticular smellparticle that our

nose can recognize.

MICRO-DETAILS: THE TONGUE

MICRO-DETAILS: THE NOSE

A dentistchecks thatyour teeth

are healthyand that nocavities aredeveloping.

NeckWhere the gum

folds in anddown around

the tooth at thegum surface.

28

• The upper jaw bone is called themaxilla.

• The lower jaw bone is called themandible.

• The mandible is the largest andstrongest bone of the face.

• The mandible has some of thehardest, toughest bone in the body.

• One of the main chewing musclesis the temporalis, which runs fromthe temple (side of the headabove the ear) to the lower side of the lower jaw.

• Another main chewing muscle isthe masseter, which runs from thecheekbone to the lower side ofthe lower jaw.

Bite small pieces of largeitems of food.

Crush food into softer pieces.

Chew these into even softerpieces for easier swallowing.

Teeth are the hardest parts of the whole body. We use them hundreds

of times each day as we bite and chew. But they are the only body

parts that cannot try to heal themselves if damaged or diseased. Not

only do teeth break down the food we eat into smaller pieces, but they also

work with the tongue to help us speak.

TEETH AND JAW

WHAT TEETH DO

The two jaw bones form thelowest parts of the face including

the chin and lower cheeks.

WHERE IN THE BODY?

Baby, milk, or deciduous:8 incisors4 canines8 premolars Total: 20 in full setBaby teeth are important becausethey help the adult teeth to growinto the correct shape.

Adult or permanent:8 incisors4 canines8 premolars12 molars Total: 32 in full set

NUMBERS OF TEETH

The roof of the mouth hastwo main parts.

• The front part behind the noseis called the hard palate.

• It is formed by a backward-facing curved plate of theupper jaw bone (maxilla) pluspart of another skull bonebehind this, the palatine bone.

• The rear part above the back of the mouth is the soft palate.

• This is made mainly ofmuscles, cartilage (gristle)and fibers.

• It can bend up as a lump offood is pushed to the back of the mouth for swallowing.

TWO ROOFS

CaninesLonger and pointed,

for ripping.

PremolarsFairly wide and low,

for chewing.

MolarsWide and low with lumpy

surfaces, for chewing.

IncisorsThin and

straight-edgedlike tiny spades,

for slicing.

maxilla

mandible

• See pages 14–17 for information on bones.


on muscles.

• See page 50–51STAGES OF LIFE

JAWS AND CHEWING

TOOTH NAMES AND SHAPES

29

F A C T S A B O U TS A L I V AWe could not chew andswallow without saliva. It would be very difficult to eat.

Chewing• It moistens food so it is easier

to chew.

• The moist food can be formedinto a lump that slips down easilywhen swallowed.

• Our taste sensors do not work aswell when food is dry, so salivagives dry food its taste.

Enzymes• Chemicals called enzymes in saliva

begin to digest the food as it ischewed, especially starchy foodslike potato, bread, rice, and pasta.

Hygiene• Saliva washes away small

particles of food and helps tokeep the mouth clean.

Teeth When baby teeth appear When adult teeth appear(months) (years)

1st incisors 6–12 6–82nd incisors 9–15 7–9Canines 14–20 9–121st premolars 15–20 10–122nd premolars 24–30 10–121st molars --- 6–72nd molars --- 11–133rd molars --- 18–21

FALLING OUT, GROWING IN• Eye teeth are called canines.

• Wisdom teeth are the rear-mostmolars, not appearing until aperson is grown up andsupposedly more experiencedand wiser than when a child.

• In some people the wisdomteeth never grow above thegum.

FUNNY NAMES

PARTS OF A TOOTH

CrownThe part of the toothabove the gum.

CementumThe “living glue” thatsticks the tooth’s rootinto the jaw.

DentineSlightly softer but stilltough layer under theenamel of the crown

and forming the outerlayer of the root.

Root canal Small tunnel-like hole atbase of root, where theblood vessels and nervesgo from the jaw bone intothe pulp.

Dental pulp Soft innermost layer ofthe tooth, made mainlyof blood vessels andnerve ends.

RootThe part of the tooth

fixed into the jaw bone.

H O W S A L I V A I SM A D E

Saliva is made in sixsalivary glands around the face.• The parotid glands are below

and to the front of each ear.

• The submandibular glands arein the angle of the lower jaw.

• The sublingual glands are in thefloor of the mouth below the tongue.

• Together the six glands make atotal of about 3 pints of salivaeach day.

• See page 38–39 forinformation on digestion.• All mouths are full of bacteria,

although not all are harmful.

• Without proper brushing, bacteriawill form on the hard enamel ofthe teeth.

• The bacteria multiply and form a film over the enamel. This iscalled plaque.

• Sugary foods help the plaquestick on to the tooth enamel.

• Sugar will also make the plaqueproduce acid, which eats into thetooth enamel.

• The acid makes tiny holes in theenamel. These get bigger and arecalled cavities.

• The tooth does not hurt until theacid reaches the nerves. By then,the cavity is already there.

PLAQUE DANGER

A dentistchecks thatyour teeth

are healthyand that nocavities aredeveloping.

NeckWhere the gum

folds in anddown around

the tooth at thegum surface.

28

• The upper jaw bone is called themaxilla.

• The lower jaw bone is called themandible.

• The mandible is the largest andstrongest bone of the face.

• The mandible has some of thehardest, toughest bone in the body.

• One of the main chewing musclesis the temporalis, which runs fromthe temple (side of the headabove the ear) to the lower side of the lower jaw.

• Another main chewing muscle isthe masseter, which runs from thecheekbone to the lower side ofthe lower jaw.

Bite small pieces of largeitems of food.

Crush food into softer pieces.

Chew these into even softerpieces for easier swallowing.

Teeth are the hardest parts of the whole body. We use them hundreds

of times each day as we bite and chew. But they are the only body

parts that cannot try to heal themselves if damaged or diseased. Not

only do teeth break down the food we eat into smaller pieces, but they also

work with the tongue to help us speak.

TEETH AND JAW

WHAT TEETH DO

The two jaw bones form thelowest parts of the face including

the chin and lower cheeks.

WHERE IN THE BODY?

Baby, milk, or deciduous:8 incisors4 canines8 premolars Total: 20 in full setBaby teeth are important becausethey help the adult teeth to growinto the correct shape.

Adult or permanent:8 incisors4 canines8 premolars12 molars Total: 32 in full set

NUMBERS OF TEETH

The roof of the mouth hastwo main parts.

• The front part behind the noseis called the hard palate.

• It is formed by a backward-facing curved plate of theupper jaw bone (maxilla) pluspart of another skull bonebehind this, the palatine bone.

• The rear part above the back of the mouth is the soft palate.

• This is made mainly ofmuscles, cartilage (gristle)and fibers.

• It can bend up as a lump offood is pushed to the back of the mouth for swallowing.

TWO ROOFS

CaninesLonger and pointed,

for ripping.

PremolarsFairly wide and low,

for chewing.

MolarsWide and low with lumpy

surfaces, for chewing.

IncisorsThin and

straight-edgedlike tiny spades,

for slicing.

maxilla

mandible

• See pages 14–17 for information on bones.


on muscles.

• See page 50–51STAGES OF LIFE

JAWS AND CHEWING

TOOTH NAMES AND SHAPES

EnamelVery hard outer covering of the

crown, up to 0.08 in. thick.

submandibular glands

sublingual glands

parotidglands

Spread out flat, all the alveolifrom both lungs would cover

a tennis court.

NOSEHairs in the nostrils filter out dustand germs, the slimy mucus lining

in the nasal chamber traps dirtand germs, and this blood-richlining also warms and dampensincoming air.

BRONCHIMain tubes branching from the

base of the windpipe, the left one 1 in. long, and right

one 2 in. long.

WINDPIPE (TRACHEA)About 4.3 in. long and

0.6–0.8 in. wide, kept openby 16–20 C-shaped pieces

of ringed cartilage.

BRONCHIOLESSmaller airways

branching fromthe mainbronchi.

TERMINALBRONCHIOLES

Smallest air tubes,thinner than hairs,formed after about15–17 branchingsfrom the mainbronchi.

30

The body’s breathing or respiratory system obtains the vital substance

oxygen from the air around us. Oxygen is needed to take part in the

body chemistry that breaks apart blood sugar, called glucose,

releasing its energy to power almost every body process and action. The main

parts of the system are the lungs, reached by the series of airways leading

down through the nose, throat, and windpipe.

LUNGS AND BREATHING

Air is expelled from ourlungs at different rates.

Normal breathing –6.5 feet per second

Fast breathing –23 feet per second

Coughing –65 feet per second

Sneeze –96 feet per second

Fresh air breathed in

79% nitrogen

20% oxygen

0.03% carbon dioxide

Stale air breathed out

79% nitrogen

16% oxygen

4% carbon dioxide

These are average volumes for an adult man. For women, theamounts are about one-quarter less.

All the air in the lungs when fully breathed in: 12.6 pintsAir in the lungs left after completely breathing out: 2.5 pintsAir between breathing out normally, and breathing out forcefully and completely: 2 pintsAir breathed in and out at rest: 17 fl. oz.Extra air when breathing in very forcefully: 7 pintsNormal breathing rate at rest: 15 in-and-out per minuteBreathing rate after great activity: 50 per minuteAmount of air breathed in and out after great activity: 6.3 pints

• The amount of air going into and coming out of lungs per minute variesfrom 1.9 gallons at rest to 40 gallons after strenuous activity.

AIR AND BREATHING RATES

HOW AIR CHANGES

AIR SPEEDS

• See page 32 for the heart rate during exercise.

• Each lung is shaped almost likea cone.

• The upper point, or apex,reaches slightly higher than thecollar bone across the top ofthe chest to the shoulder.

• The wide base sits on thedome-shaped main breathingmuscle, the diaphragm, whichis roughly level with the bottomof the breastbone but curvesdown to the bottom ribs aroundthe sides.

• The left lung has two mainparts, or lobes, and a scooped-out shape where the heart fits.

• The right lung has three lobesand is on average about one-fifth bigger than the left lung.

SIZE AND SHAPE OF THE LUNGS

• Volume of air passing throughthe lungs in a year: 1,056,000gallons.

• Number of breaths in a lifetime:about 500 million.

TOTAL BREATHINGAir enters the respiratory systemthrough the nose or mouth and

travels down the windpipe to thelungs in the chest.

WHERE IN THE BODY?

• See pages 26–27 for information on the nose.

feet per second

100 ft.

75 ft.

50 ft.

25 ft.

0 ft.

feet

nitrogen

oxygenother

nitrogen

oxygenother

31

B R E A T H I N G A N DSPEECHAir passing out of the lungs has a useful extraeffect—speech.• There are nine pieces of cartilage

in the larynx.

• Front ridge of the thyroidcartilage forms the “Adam’sapple” that males and femaleshave, but is more noticeable inmales.

• About 19 muscles of the larynxalter the length of the vocal cords,called vocal folds, to make thesounds of speech.

• The vocal cords are about 0.2 in.longer in men than women,giving a deeper voice.

• Average pitch of male vocalcords: 120 Hz (vibrations persecond).

• Average pitch of female vocalcords: 220 Hz (vibrations per second).

• Average pitch of child’s vocalcords: 260 Hz (vibrations persecond).

The places where oxygen istaken into the body are tinybubble-shaped spaces deep in the lungs, called alveoli.

• Alveoli are bunched at the end of the smallest airways, the terminalbronchioles.

• There are 250-300 million alveoli in each lung.

• Breathing not only takes in oxygen,it also gets rid of the waste productcarbon dioxide, which would soonpoison the body if it was notexpelled.

BRANCHING AIRWAYS

T H EVOICEBOX

Above the voicebox is the leaf-shaped flap of epiglottis cartilage.When food is swallowed, this foldsdown over the entrance to thevoicebox to prevent food enteringthe airway and causing choking.

Spread out flat, all the alveolifrom both lungs would cover

a tennis court.

NOSEHairs in the nostrils filter out dustand germs, the slimy mucus lining

in the nasal chamber traps dirtand germs, and this blood-richlining also warms and dampensincoming air.

BRONCHIMain tubes branching from the

base of the windpipe, the left one 1 in. long, and right

one 2 in. long.

WINDPIPE (TRACHEA)About 4.3 in. long and

0.6–0.8 in. wide, kept openby 16–20 C-shaped pieces

of ringed cartilage.

BRONCHIOLESSmaller airways

branching fromthe mainbronchi.

TERMINALBRONCHIOLES

Smallest air tubes,thinner than hairs,formed after about15–17 branchingsfrom the mainbronchi.

30

The body’s breathing or respiratory system obtains the vital substance

oxygen from the air around us. Oxygen is needed to take part in the

body chemistry that breaks apart blood sugar, called glucose,

releasing its energy to power almost every body process and action. The main

parts of the system are the lungs, reached by the series of airways leading

down through the nose, throat, and windpipe.

LUNGS AND BREATHING

Air is expelled from ourlungs at different rates.

Normal breathing –6.5 feet per second

Fast breathing –23 feet per second

Coughing –65 feet per second

Sneeze –96 feet per second

Fresh air breathed in

79% nitrogen

20% oxygen

0.03% carbon dioxide

Stale air breathed out

79% nitrogen

16% oxygen

4% carbon dioxide

These are average volumes for an adult man. For women, theamounts are about one-quarter less.

All the air in the lungs when fully breathed in: 12.6 pintsAir in the lungs left after completely breathing out: 2.5 pintsAir between breathing out normally, and breathing out forcefully and completely: 2 pintsAir breathed in and out at rest: 17 fl. oz.Extra air when breathing in very forcefully: 7 pintsNormal breathing rate at rest: 15 in-and-out per minuteBreathing rate after great activity: 50 per minuteAmount of air breathed in and out after great activity: 6.3 pints

• The amount of air going into and coming out of lungs per minute variesfrom 1.9 gallons at rest to 40 gallons after strenuous activity.

AIR AND BREATHING RATES

HOW AIR CHANGES

AIR SPEEDS

• See page 32 for the heart rate during exercise.

• Each lung is shaped almost likea cone.

• The upper point, or apex,reaches slightly higher than thecollar bone across the top ofthe chest to the shoulder.

• The wide base sits on thedome-shaped main breathingmuscle, the diaphragm, whichis roughly level with the bottomof the breastbone but curvesdown to the bottom ribs aroundthe sides.

• The left lung has two mainparts, or lobes, and a scooped-out shape where the heart fits.

• The right lung has three lobesand is on average about one-fifth bigger than the left lung.

SIZE AND SHAPE OF THE LUNGS

• Volume of air passing throughthe lungs in a year: 1,056,000gallons.

• Number of breaths in a lifetime:about 500 million.

TOTAL BREATHINGAir enters the respiratory systemthrough the nose or mouth and

travels down the windpipe to thelungs in the chest.

WHERE IN THE BODY?

• See pages 26–27 for information on the nose.

feet per second

FAIR EXCHANGE

Air passes through a series ofchambers and tubes on its wayto deep in the lungs.

The total length of all the air tubes in the lungs joined end to end is about 31 miles.

• See page 54 forinformation on the tonsils.

THROAT A passageway for

both food and air.

100 ft.

75 ft.

50 ft.

25 ft.

0 ft.

feet

nitrogen

oxygenother

nitrogen

oxygenother

THE HEART

The heart is between the lungs.It tips slightly to the left side,which is why people think it ison the left side of the body.

PULSE RATE (HEARTBEATS) PER MINUTE

The right and left sides ofthe heart work side-by-sidelike two pumps. Every time the heart contracts, or beats, the right side pumpsoxygen-poor blood back to thelungs to pick up oxygen, and theleft side pumps oxygen-rich bloodfrom the lungs out into the body.

THE HEART’S JOB

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In the center of your chest, below a thin layer of skin, muscle, and bone,

sits your heart. This simple, yet essential, pump carries blood to and

from your body’s billions of cells nonstop, day and night. During an

average lifetime of 70 years, the heart beats 2.5 billion times. Without the

heart’s second-by-second collection and delivery service, your cells—and

your body—would die.

WHAT MAKES THE HEART BEAT?

The muscle that makes up the walls of the heart, called cardiac muscle or

myocardium, never ceases workingand needs a continuous supply

of blood. Two coronary arteries

branch off from the aorta to

carry essentialsupplies to the heart’s cells.

THE HEART’S OWN BLOOD SUPPLY

The number of heartbeats per minute is called the pulse rate. The resting heart ratechanges throughout our lives. When we exercise, our heart needs to supply moreoxygen to our bodies, so it pumps harder and faster.

At the top of the heart is a tiny areacalled the sinoatrial node. It sends

out electrical signals that make thecells in the heart wall contract.

32

The heart is about the size of its owner’s clenched fist. As yougrow from a child into an adult, your heart will grow at the samerate as your clenched fist.

PHYSICAL CHARACTERISTICS

Average heart weight male: 10.5 oz.Average heart weight female: 8.8 oz.

Size: Length: 4.7 in.Width: 3.1–3.5 in.Front to back: 2.3 in.

WHERE IN THE BODY?

coronary arteries

Dotted lines represent oxygen-poor blood1) Blood flows in from the body to the right

atrium through the superior and inferior vena cavas.It is known as oxygen-poor blood because the bodyhas taken and used the oxygen that the blood wascarrying.

2) The right atrium pumps the blood throughthe tricuspid valve into the right ventricle.

3) The right ventricle pumps the bloodthrough the pulmonary valve into the pulmonaryartery and off into the lungs.

Inside the lungs4) As the blood travels through the lungs, it releaseswaste gases and picks up oxygen.

Dashed lines represent oxygen-rich blood5) The blood flows from the lungs into the

left atrium through the pulmonary veins.

6) The left atrium pumps the blood into theleft ventricle.

7) The left ventricle pumps the blood throughthe aortic valve into the aorta and off around the body.

P A R T S O F T H EH E A R T

AortaThe largest artery in the body. It is about the diameter of a garden hose.

AtriumOne of the two small upperchambers in the heart thatreceives blood from the veins andpasses it to the ventricles below.

HeartstringsCords that hold the valve in place between the atrium andthe ventricle.

Inferior Vena CavaA large vein that collects bloodfrom the lower half of the body.

PericardiumThe tough outer covering of the heart.

SeptumMuscular wall that divides the left and right sides of the heart.

Superior Vena CavaA large vein which collects bloodfrom the upper half of the body.

ValveA sort of door that only opensone way to let blood through, but stops it flowing backwards.The heart has four valves: thetricuspid, pulmonary, mitral, andaortic valves.

VentricleOne of the two large lowerchambers in the heart thatreceives blood from the atriumabove and passes it out into the arteries.

Superior (upper)vena cava

Inferior(lower)

vena cava

Tricuspidvalve

Pulmonaryvalve

Mitralvalve

Septum

Rightventricle

Heartstrings

Muscular wallof cardiac

(heart) muscle

Left ventricle

Right atrium

Sinoatrialnode

Leftatrium

Pericardium

Aorta

Pulmonary veins

THE HEART (VIEWED FROM THE FRONT)

An average adult heart:• Pumps 2.3 fl. oz. of blood

per heartbeat.

• Pumps 10.5 pints of blood perminute.

• Pumps 1,900 gallons of blood each day.

• Beats 100,000 times each day.

• Circulates the body’s blood 1000 times each day.

A DAY IN THE LIFE OF THEH E A R T

Pulmonary artery

33

THE HEART

The heart is between the lungs.It tips slightly to the left side,which is why people think it ison the left side of the body.

PULSE RATE (HEARTBEATS) PER MINUTE

The right and left sides ofthe heart work side-by-sidelike two pumps. Every time the heart contracts, or beats, the right side pumpsoxygen-poor blood back to thelungs to pick up oxygen, and theleft side pumps oxygen-rich bloodfrom the lungs out into the body.

THE HEART’S JOB

200

175

150

125

100

75

50

25

0

New

born

3 m

onth

s

6 m

onth

s

1 ye

ar

3-6

year

s

8 ye

ars

AD

ULT

at

res

t

AD

ULT

ru

nnin

g

In the center of your chest, below a thin layer of skin, muscle, and bone,

sits your heart. This simple, yet essential, pump carries blood to and

from your body’s billions of cells nonstop, day and night. During an

average lifetime of 70 years, the heart beats 2.5 billion times. Without the

heart’s second-by-second collection and delivery service, your cells—and

your body—would die.

WHAT MAKES THE HEART BEAT?

The muscle that makes up the walls of the heart, called cardiac muscle or

myocardium, never ceases workingand needs a continuous supply

of blood. Two coronary arteries

branch off from the aorta to

carry essentialsupplies to the heart’s cells.

THE HEART’S OWN BLOOD SUPPLY

The number of heartbeats per minute is called the pulse rate. The resting heart ratechanges throughout our lives. When we exercise, our heart needs to supply moreoxygen to our bodies, so it pumps harder and faster.

At the top of the heart is a tiny areacalled the sinoatrial node. It sends

out electrical signals that make thecells in the heart wall contract.

32

The heart is about the size of its owner’s clenched fist. As yougrow from a child into an adult, your heart will grow at the samerate as your clenched fist.

HOW THE HEART WORKS

PHYSICAL CHARACTERISTICS

Average heart weight male: 10.5 oz.Average heart weight female: 8.8 oz.

Size: Length: 4.7 in.Width: 3.1–3.5 in.Front to back: 2.3 in.

WHERE IN THE BODY?

coronary arteries

34

Something that circulates goes around and around, and that’s exactly

what your blood does inside your body. Pumped by your heart, your

blood flows around a network of pipes and tubes called blood vessels,

on a nonstop, never-ending journey around your body. The blood vessels,

together with the heart and blood, all make up the circulatory system.

• Arteries carry blood from the heart,but not all of this blood is high inoxygen.

• The pulmonary arteries from the rightside of the heart to the lungs carryblood low in oxygen.

• Similarly, veins carry blood to theheart, but not all of this blood is lowin oxygen.

• The pulmonary veins from the lungsto the left side of the heart carryblood high in oxygen.

LENGTH AND AREAThe journey time for anytiny drop of blood dependson its route around thecirculatory system.

• A short trip from the heart’sright side to the lungs andstraight back to the heart’s leftside can take less than 10 seconds.

• A long trip from the heart’s leftside all the way down throughthe body and legs to the toes,then all the way back theheart’s right side, can take more than a minute.

CIRCULATORY SYSTEM

Blood vessels reach every tinypart of your body from the topof your head to the ends of yourfingers and toes. • Some parts have much fewer

blood vessels than others, suchas the tough, tapering tendons atthe ends of muscles, which havemore than 10 times fewer bloodvessels than the muscle itself.

• Only a few small body partshave no blood vessels at all, forexample, the lens of the eye.

WHERE IN THE BODY?

The circulatory system isalso called thecardiovascular system.

• Cardio comes from the ancientGreek word kardia that meansheart.

• Vascular comes from the Latinword vas that means vessel.

• The vessels leading to and fromeach body part are known as itsvascular supply.

DIFFERENT NAMES

Veins• The main vein bringing blood

from the head, arms, and upperbody back to the heart is calledthe superior vena cava.

• The main vein bringing bloodfrom the lower body, hips, andlegs back the heart is called theinferior vena cava.

• Both these main veins are about1.2 in. wide.

• Blood flows very slowly throughthem, at only 0.04 in. per second.

• At any single moment, thesemain veins contain one-tenth ofall the body’s blood.

Arteries• The body’s main artery is the

aorta, carrying blood from theleft side of the heart to allbody parts.

• The aorta is 15.7 in. long andarches up, over, and behind theheart, inside the chest.

• The aorta’s width is about0.98 in.

• Its walls are 0.1 in. thick.

• Blood surges through the aorta at about 1.18 in. per second.

Exercise pumps the blood around the body faster.

MAIN VEINS AND ARTERIES


• See pages 30–31 forinformation on the lungs.

heart

Blood that has a lot of oxygen in it is red. When the body has used theoxygen, the blood becomes blue.

BLUE AND RED

pulmonary veins

pulmonary arteries

inferior vena cava

aorta

3534

Something that circulates goes around and around, and that’s exactly

what your blood does inside your body. Pumped by your heart, your

blood flows around a network of pipes and tubes called blood vessels,

on a nonstop, never-ending journey around your body. The blood vessels,

together with the heart and blood, all make up the circulatory system.

• Arteries carry blood from the heart,but not all of this blood is high inoxygen.

• The pulmonary arteries from the rightside of the heart to the lungs carryblood low in oxygen.

• Similarly, veins carry blood to theheart, but not all of this blood is lowin oxygen.

• The pulmonary veins from the lungsto the left side of the heart carryblood high in oxygen.

T Y P E S O F B L O O DVESSELSArteries• Carry blood away from the

heart.

• Thick, muscular walls to copewith the surge of high pressureas blood is forced from the heartwith each heartbeat.

• Take blood to the body’s mainparts or organs.

• Divide and become thinnerforming arterioles.

Arterioles• Smaller and shorter than

arteries.

• Muscles in the walls can tightento make the arterioles smaller, orrelax and make them wider tocontrol amount of blood flowingthrough.

• Divide and become narrower,forming capillaries.

Capillaries• The smallest blood vessels, very

short and too thin to see withouta microscope.

• Walls are so thin (just one cellthick) that nutrients and usefulsubstances can pass from theblood inside, through the wallsto cells and tissues around.

• Thin walls also allow wastes andunwanted substances to passfrom cells and tissues around,into the blood, to be taken away.

• Join together to form venules.

Venules• Thin-walled and very flexible.

• Collect blood from within eachmain body part.

• Join together, forming veins.

Veins• Wide, with thin, floppy walls.

• Have pocket-like valves stickingout from their walls, to makesure blood flows the correct way.

• Carry blood from main bodyparts back to the heart.

Blood vessel Typical diameter across (in.) Wall thickness(in.) Typical length (in.) Blood pressure inside (blood emerging from heart = max 100)

Arteries 0.2 0.4 6 90Arterioles 0.019 0.0007 0.2 60Capillaries 0.00003 0.00004 0.02 30Venules 0.0007 0.000001 0.1 20Veins 0.6 0.019 6 10

• If all the body’s blood vesselscould be taken out and joined endto end, they would stretch about62,137 m., which is two and a half times around the world.

• If all the capillaries were ironedflat their total surface area wouldbe about half a soccer field.

NAMING THE PARTS

LENGTH AND AREAThe journey time for anytiny drop of blood dependson its route around thecirculatory system.

• A short trip from the heart’sright side to the lungs andstraight back to the heart’s leftside can take less than 10 seconds.

• A long trip from the heart’s leftside all the way down throughthe body and legs to the toes,then all the way back theheart’s right side, can take more than a minute.

CIRCULATORY SYSTEM

JOURNEY TIMES

Blood vessels reach every tinypart of your body from the topof your head to the ends of yourfingers and toes. • Some parts have much fewer

blood vessels than others, suchas the tough, tapering tendons atthe ends of muscles, which havemore than 10 times fewer bloodvessels than the muscle itself.

• Only a few small body partshave no blood vessels at all, forexample, the lens of the eye.

WHERE IN THE BODY?

The circulatory system isalso called thecardiovascular system.

• Cardio comes from the ancientGreek word kardia that meansheart.

• Vascular comes from the Latinword vas that means vessel.

• The vessels leading to and fromeach body part are known as itsvascular supply.

DIFFERENT NAMES

Coronary arteries carryblood to the heart’s

muscular walls, and arenamed because their

branching shape looks like a crown (corona)

around the heart.

Gastric artery andvein for the stomach.

Hepatic artery andvein for the liver.

Renal artery and veinfor the kidney.

Iliac artery and vein to the leg.

Cerebral vessels in the head.

Veins• The main vein bringing blood

from the head, arms, and upperbody back to the heart is calledthe superior vena cava.

• The main vein bringing bloodfrom the lower body, hips, andlegs back the heart is called theinferior vena cava.

• Both these main veins are about1.2 in. wide.

• Blood flows very slowly throughthem, at only 0.04 in. per second.

• At any single moment, thesemain veins contain one-tenth ofall the body’s blood.

Arteries• The body’s main artery is the

aorta, carrying blood from theleft side of the heart to allbody parts.

• The aorta is 15.7 in. long andarches up, over, and behind theheart, inside the chest.

• The aorta’s width is about0.98 in.

• Its walls are 0.1 in. thick.

• Blood surges through the aorta at about 1.18 in. per second.

Exercise pumps the blood around the body faster.

MAIN VEINS AND ARTERIES

• See pages 32–33 forinformation on THE HEART.


• See pages 30–31 forinformation on the lungs.

heart

Blood that has a lot of oxygen in it is red. When the body has used theoxygen, the blood becomes blue.

BLUE AND RED

BLOOD VESSEL CHART

Most arteries and veins are named from thebody parts they supply.


on THE BRAIN.


on the stomach.

pulmonary veins

pulmonary arteries

inferior vena cava

aorta

36

Pumped by the heart, blood flows through tubes, called blood vessels,

to every part of the body. Blood carries useful substances like oxygen

and nutrients to all body parts. It also collects wastes and unwanted

substances that are removed mainly by the kidneys. But the blood does much

much more than just delivering oxygen and picking up waste.

In general, busier body partsneed more blood supply.

• When a body part is active,changes occur in the bloodvessels in order to supply it with more blood.

• The muscles in the walls of thesmall blood vessels, calledarterioles, relax.

• This allows more blood to flowthrough them to the part theysupply.

• The width of the arterioles iscontrolled mainly by signalsfrom the brain sent along nerves.

• The hormone adrenaline alsoaffects the width of the arterioles.

BLOOD FLOW THROUGHBODY PARTS

A pinhead-sized drop ofblood, contains:

• 5 million red blood cells.

• 5,000 white blood cells.

• 250,000 platelets.

If a person is ill, the number ofgerm-fighting white cells in bloodmay rise from 5,000 to 25,000.

BLOOD

At any single moment about 1⁄6 of all the body’s blood isin the arteries, almost 3⁄4 is in theveins, and less than 1⁄20 is in the

tiny capillaries inside body parts or organs.

WHERE IN THE BODY?

The amount of blood in thebody depends mainly onbody size.

• On average, blood is 1⁄12

of the body’s total weight.

• This is slightly less in womencompared to men.

• Most women naturally havemore fatty tissue than men,which has less blood supplycompared to other body parts.

• Also, most women naturallyhave less muscle tissue thanmen, which has more bloodsupply compared to other body parts.

• An average adult female has8.4–10.5 pints of blood.

• An average adult male has10.5–12.6 pints of blood.

• For people of average weightand build, the volume of bloodis about 1.8 fl. oz. per lb. ofbody weight.

HOW MUCH?

The four different blood types were discovered in 1900. Before this,blood transfusions had a high rate of failure. Today, we realize it isvital to know the blood types of the donor and the patient in order forblood to be used safely.

• Certain kinds or groups of blood,when mixed together, may formclumps or clots.

• This can be dangerous during ablood transfusion, when bloodis given or donated by oneperson, to be put into anotherperson, the recipient .

• ABO is the system for testingblood for its group. A personcan be either A, B, AB, or O.

• A person with type O is a universaldonor, whose blood can be givento almost anyone. A person withtype AB is a universal recipient,who can receive blood fromalmost anyone.

Blood type Can donate Can receiveof person blood to blood from

A A, AB A, OB B, AB B, OAB AB A, B, AB, OO A, B, AB, O O


• See pages 34–35 for information on theCIRCULATORY SYSTEM.

BLOOD TYPES

3736

Pumped by the heart, blood flows through tubes, called blood vessels,

to every part of the body. Blood carries useful substances like oxygen

and nutrients to all body parts. It also collects wastes and unwanted

substances that are removed mainly by the kidneys. But the blood does much

much more than just delivering oxygen and picking up waste.

W H A T I S I NBLOOD?

Blood is mostly made up ofplasma and red blood cells.White blood cells andplatelets make up a tinyproportion of the total.

Plasma• Forms just over half of blood by

volume.

• Pale, tan color.

• Over nine-tenths is water.

• Contains many dissolvedsubstances, such as glucose,hormones, body salts, andminerals, unwanted wastes suchas urea, disease-fightingantibodies, and dozens of others.

Red blood cells• Nearly half of all blood.

• Also called erythrocytes.

• Carry oxygen from the lungs allaround the body.

• Pick up carbon dioxide to takeback to the lungs for removal.

White blood cells

• Form less than 1⁄100 of blood.

• Also called leucocytes.

• Attack, disable, and kill invadinggerms.

• Engulf or eat waste bits such aspieces of old, broken-down cells.

Platelets

• Form less than 1⁄100 of blood.

• Also called thrombocytes.

• Are not so much whole livingmicroscopic cells, but parts orfragments of cells.

• Help blood to clot (thrombose) toseal cuts and wounds.

In general, busier body partsneed more blood supply.

• When a body part is active,changes occur in the bloodvessels in order to supply it with more blood.

• The muscles in the walls of thesmall blood vessels, calledarterioles, relax.

• This allows more blood to flowthrough them to the part theysupply.

• The width of the arterioles iscontrolled mainly by signalsfrom the brain sent along nerves.

• The hormone adrenaline alsoaffects the width of the arterioles.

BLOOD FLOW THROUGHBODY PARTS

Red blood cells carry oxygenaround the body.

• Red blood cells are among themost numerous cells, with 25,000billion in an average person.

• They are also among the smallestcells, each one just 7 microns,0.000028 in., across and 2microns thick.

• Each red cell is shaped like a doughnut withoutthe hole pokedcompletely though.

• A red cell’s color is due to thesubstance haemoglobin.

• Haemoglobin joins or attaches tooxygen and carries it around the body.

• Each red cell contains 250 milliontiny molecules of haemoglobin.

• Each red blood cell lives for threeor four months, then dies and isbroken apart.

• This means about 3 million redblood cells die every second – and the same number of newones are made.

• Red blood cells, like white bloodcells and platelets, are made inthe jelly-like marrow insidebones.

RED BLOOD CELLS

A pinhead-sized drop ofblood, contains:

• 5 million red blood cells.

• 5,000 white blood cells.

• 250,000 platelets.

If a person is ill, the number ofgerm-fighting white cells in bloodmay rise from 5,000 to 25,000.

BLOOD

IN ONE DROP OFBLOOD

At any single moment about 1⁄6 of all the body’s blood isin the arteries, almost 3⁄4 is in theveins, and less than 1⁄20 is in the

tiny capillaries inside body parts or organs.

WHERE IN THE BODY?

The amount of blood in thebody depends mainly onbody size.

• On average, blood is 1⁄12

of the body’s total weight.

• This is slightly less in womencompared to men.

• Most women naturally havemore fatty tissue than men,which has less blood supplycompared to other body parts.

• Also, most women naturallyhave less muscle tissue thanmen, which has more bloodsupply compared to other body parts.

• An average adult female has8.4–10.5 pints of blood.

• An average adult male has10.5–12.6 pints of blood.

• For people of average weightand build, the volume of bloodis about 1.8 fl. oz. per lb. ofbody weight.

HOW MUCH?

plasma

other

red bloodcells

The four different blood types were discovered in 1900. Before this,blood transfusions had a high rate of failure. Today, we realize it isvital to know the blood types of the donor and the patient in order forblood to be used safely.

• Certain kinds or groups of blood,when mixed together, may formclumps or clots.

• This can be dangerous during ablood transfusion, when bloodis given or donated by oneperson, to be put into anotherperson, the recipient .

• ABO is the system for testingblood for its group. A personcan be either A, B, AB, or O.

• A person with type O is a universaldonor, whose blood can be givento almost anyone. A person withtype AB is a universal recipient,who can receive blood fromalmost anyone.

Blood type Can donate Can receiveof person blood to blood from

A A, AB A, OB B, AB B, OAB AB A, B, AB, OO A, B, AB, O O


• See pages 34–35 for information on theCIRCULATORY SYSTEM.

BLOOD TYPES

BLOOD FLOW AT REST AND AT WORK

Part of the body At rest During hardexercise

Heart 0.5 1.5Kidneys 2.5 1.2Main muscles 2.1 25.4Skin 0.8 4.2Stomach, intestines 2.9 1.2Brain 1.5 1.5

Only the brain’s blood flow stays the same no matter how activethe body is, from running a fast race to fast asleep.

Flow in pints perminute

38

Your body needs fuel to function. Food gives you the energy

to move about, walk and run, and keep your inside processes going,

like heartbeat and breathing. But food gives you more than energy.

It provides nutrients for growth, making newer and bigger body parts,

repairing old worn-out ones, and staying healthy, too. The parts of the body

specialized to take in and break down foods into tiny pieces form the

digestive system.

The stomach is a J-shapedbag behind the left lower ribs.

• Measures about 12 in. around itslonger side.

• Has thick muscle layers in its wallsthat squirm and squeeze to mashthe food inside.

• Average amount of food and drinkcontents is 3 pints.

• Lining makes about 3 pints ofgastric juices each day.

• Gastric juices include hydrochloricacid and digestive chemicals, calledenzymes—pepsin attacks proteinsin food, and lipase attacks fats.

• Takes in or absorbs few nutrients,including sugars.

• Lining also makes thick slimymucus, to protect the stomach’sgastric juices from digesting itself.

FOOD’S JOURNEYPart of tract Length (in.) Time spent by food

Mouth 3.9 Up to 1 minuteThroat 3.9 2–4 secondsEsophagus 10 2–5 secondsStomach 10 3–6 hoursSmall intestine 228 2–4 hoursLarge intestine 60 5–10 hoursRectum 7.8 5–8 hours

FOOD’S JOURNEY

THE DIGESTIVE TRACTDIGESTION

The digestive system starts at themouth and ends at the anus. Mostof its main parts, the stomach andintestines, are in the abdomen(lower half of the main body).

WHERE IN THE BODY?

• The digestive system makes morethan 2.6 gallons of digestivejuices each day.

• Most of the water in these juices istaken back into the body by thelarge intestine.

• Only about 0.3 fl. oz. is lost in thewastes from the system.

• The digestive system recycles99⁄100 of its water.

RECYCLING

The appendix is a finger-sized part of the body,branching from the start of the large intestine.

• It is a dead end, with its tipsealed.

• Hollow inside.

• Varies in length from 2–6 in.

• Seems to have no important taskin digestion (or anything else).

APPENDIX:A PUZZLING PART

The appendix may swell upwith “stuck” food and germs,

causing appendicitis withsevere pain in the lower

right abdomen.

STOMACH

liver

stomach

small intestine

large intestine

3938

Your body needs fuel to function. Food gives you the energy

to move about, walk and run, and keep your inside processes going,

like heartbeat and breathing. But food gives you more than energy.

It provides nutrients for growth, making newer and bigger body parts,

repairing old worn-out ones, and staying healthy, too. The parts of the body

specialized to take in and break down foods into tiny pieces form the

digestive system.

• Without food inside, most of thedigestive passageway issqueezed flat by the naturalpressure inside the body.

• Food has to be pushed throughthe passageway by waves ofmuscle action in its walls, calledperistalsis.

S M A L LI N T E S T I N E

• Average width is 1.1–1.3 in.

• Has three main parts: duodenum(10 in.), jejunum (88 in.) andileum (118 in.).

• Receives digestive juices from the pancreas and liver.

• Inner surface has many folds,called plicae.

• On these folds are tiny finger-like shapes, villi, about 0.4 in.long.

• All the villi joined end to endwould stretch 248 miles.

• On each villus are even moremicroscopic finger-like shapes,microvilli.

• Plicae, villi, and microvilli greatlyincrease surface area of inside of small intestine, to about6–12 sq yd., to absorb as manynutrients as possible from food.

The stomach is a J-shapedbag behind the left lower ribs.

• Measures about 12 in. around itslonger side.

• Has thick muscle layers in its wallsthat squirm and squeeze to mashthe food inside.

• Average amount of food and drinkcontents is 3 pints.

• Lining makes about 3 pints ofgastric juices each day.

• Gastric juices include hydrochloricacid and digestive chemicals, calledenzymes—pepsin attacks proteinsin food, and lipase attacks fats.

• Takes in or absorbs few nutrients,including sugars.

• Lining also makes thick slimymucus, to protect the stomach’sgastric juices from digesting itself.

FOOD’S JOURNEYPart of tract Length (in.) Time spent by food

Mouth 3.9 Up to 1 minuteThroat 3.9 2–4 secondsEsophagus 10 2–5 secondsStomach 10 3–6 hoursSmall intestine 228 2–4 hoursLarge intestine 60 5–10 hoursRectum 7.8 5–8 hours

FOOD’S JOURNEY

PUSHING FOOD

THE DIGESTIVE TRACTDIGESTION

The digestive system starts at themouth and ends at the anus. Mostof its main parts, the stomach andintestines, are in the abdomen(lower half of the main body).

WHERE IN THE BODY?

• The digestive system makes morethan 2.6 gallons of digestivejuices each day.

• Most of the water in these juices istaken back into the body by thelarge intestine.

• Only about 0.3 fl. oz. is lost in thewastes from the system.

• The digestive system recycles99⁄100 of its water.

RECYCLING

L A R G EI N T E S T I N E

• Average width 2.3–2.7 in.

• First part is wider, the caecum,and has the appendix branchingfrom it.

• Second part is the ascendingcolon, going up the right side of the abdomen.

• Third part is the transverse colon,across the top of the abdomen.

• Fourth part is the sigmoid(S-shaped) colon, on the lowerleft of the abdomen.

• Mainly takes back water andvaluable body salts and mineralsfrom leftover foods and wastes.

The digestive system includes the digestive tract described here, and also parts that work along with this, including the liver and pancreas. The digestive tract is the

passageway for food.

The appendix is a finger-sized part of the body,branching from the start of the large intestine.

• It is a dead end, with its tipsealed.

• Hollow inside.

• Varies in length from 2–6 in.

• Seems to have no important taskin digestion (or anything else).

APPENDIX:A PUZZLING PART

The appendix may swell upwith “stuck” food and germs,

causing appendicitis withsevere pain in the lower

right abdomen.

• The average weight of solid wasteis 5.2 oz. per day.

• The weight varies greatly,increasing with the amount of fiber in food.

Two-thirds water, about 3.5 oz.

One-ninth is dead microbes that livenaturally in the large intestine andhelp with digestion.

One-ninth or more of the rest is undigested food,

especially fiber.

One-ninth is rubbed-off parts of thedigestive lining.

There are about 500 millionvilli in the body.

In the esophagus, peristalsisis so strong it works even ifthe body is upside down.

STOMACH

ThroatWhere swallowed food from the

mouth passes down to the esophagus.

StomachWhere food its mashed and mixed with powerful juices containing acids

and enzymes.

Small intestineReceives part-digested,

soupy food from thestomach, adds morejuices and enzymes toit, and absorbs thevarious nutrients.

AnusThe last part of the passageway, a ring of muscle that relaxes to let out the solid waste.

MouthWhere teeth bite and chew food, thetongue moves it around, and salivary

glands add saliva to it.

EsophagusThe esophagus carries food

through the neck and chest tothe stomach.

Large intestine(colon)

Takes the leftovers fromthe small intestine,

takes in most of thewater from them, andforms them into solid

waste.

RectumStores the solid

waste.

• See page29 for information

on saliva.

• See pages42–43 for LIVER AND

PANCREAS.

• See page 41 forinformation on FIBER.

LEFTOVERSliver

stomach

small intestine

large intestine

40

Have you had plenty of lipids, complex carbohydrates, trace metallic

elements, and cellulose today? These are all substances that your

body needs to stay healthy, but their names are quite complicated.

Usually, we call these substances, and everything else the body needs to take

in every day, by a simpler name—food. However, in your food there are six

main groups of substances which you may have heard about: proteins,

carbohydrates, fats, vitamins, minerals, and fiber.

Fats are used for bothbuilding and energy.

• Broken down by digestion into smaller, simpler pieces, called lipids.

• Foods with plenty of fats areusually fatty plant parts; includingred meats; oily fish; eggs, milk,cheese, and other dairy products;and certain foods like avocados,olives, and peanuts.

• Taken in and used both forbuilding parts, such as nerves,making and repairing parts ofmicroscopic cells, and asenergy that carbohydrates arelacking.

• Too much fat from animalsources (fatty red meats andprocessed foods, like burgersand salami) is linked tovarious health problems, suchas heart disease and highblood pressure.

Carbohydrates are “energy foods.”

• Broken down by digestion intosmaller, simpler pieces, such assugars.

• Taken in and used as the body’smain source of energy, calledglucose or blood sugar, for the lifeprocesses of all its microscopic cells.

• Also used for all musclemovements from heartbeat andbreathing to fast running.

• Foods with plenty of carbohydratesare starchy or sweet, such as rice,wheat, barley, and other grains.Products made from these arepasta and bread. There are alsomany “starchy” vegetables, likepotatoes and corn, and manysweet fruits like bananas andstrawberries, as well as sugaryitems like candy and chocolate.

CARBOHYDRATES

FATS AND OILS

For an average adult with atypical office job, daily needsare:

Carbohydrates 300 grams (including 25 grams or more of fiber)

Proteins 50 grams

Fats 60 grams(mostly from plant sources)

Vitamins, examples:Vitamin C 0.06 gramVitamin K 0.00008 gram

Minerals, examples:Calcium 1 gramIron 0.018 gramChloride 3.4 grams

DAILY NEEDS

FOOD AND NUTRIENTS

Food can be divided into groups.This can help us plan a

balanced diet.

Yellow: meat and fishGreen: grainsRed: fruit and vegetablesBlue: dairy productsOrange: sugary foods

We should eat foods from eachof these groups in order to stayhealthy. We should choose moregrains, fruit, and vegetables,and eat less sugary food.

DIFFERENT SORTS OF FOOD

MINERALC H A R T

IronNeeded for: red blood cells, skin,muscles, resisting stress, fightingdisease

CalciumNeeded for: bones, teeth, nerves,heartbeat, blood clotting, kidneys

SodiumNeeded for: nerves and nervesignals, digestion, blood, chemicalprocesses inside cells, kidneys

MagnesiumNeeded for: heartbeat and rhythm,energy use

IodineNeeded for: overall speed of body’schemical processes, making thyroidhormone

ZincNeeded for: healthy immunesystem, wound healing, maintainingsenses of smell and taste

Bread is made from wheat, agood source of carbohydrates.

Fat is an importantpart of our diet,

but we should getmost of what weneed from plantsources, such as

olive oil.

Fresh fruit and vegetables are agood source of fiber, particularly

if the the skins are eaten as well.

4140

Have you had plenty of lipids, complex carbohydrates, trace metallic

elements, and cellulose today? These are all substances that your

body needs to stay healthy, but their names are quite complicated.

Usually, we call these substances, and everything else the body needs to take

in every day, by a simpler name—food. However, in your food there are six

main groups of substances which you may have heard about: proteins,

carbohydrates, fats, vitamins, minerals, and fiber.

Fiber is needed to help food passthrough our body properly.

• Sometimes called roughage.• Is not really broken down or

digested by the body. It passesthrough the digestive tract largelyunaltered.

• Needed to give food “bulk,” sothe intestines can grip it andmake it move through them.

• Helps to satisfy hunger, reducingthe temptation to eat too much.

• Reduces the risk of wastes beingtoo small and hard and gettingstuck, called constipation.

• Fiber also reduces risks of variousintestinal diseases, includingcertain kinds of colon cancer.

VITAMINC H A R T

Vitamin AChemical name: Carotene

Needed for: eyes, skin, teeth,bones, general health

Vitamin B1Chemical name: Thiamine

Needed for: brain, nerves,muscles, heart, energy use,general health

Vitamin B2Chemical name: Riboflavin

Needed for: blood, eyes, skin,hair, nails, fighting disease,general health

Vitamin B3Chemical name: Nicotinic acid

Needed for: energy use,controlling blood contents

Vitamin B6Chemical name: Pyridoxine

Needed for: chemical processesinside cells, brain, skin, muscle,energy use, general health

Vitamin B12Chemical name: Cobalamin

Needed for: blood, brain, nerves,growing, energy use, generalhealth

Vitamin BFChemical name: Folic acid

Needed for: blood, digestion,growth

Vitamin CChemical name: Ascorbic acid

Needed for: teeth, gums, bones,blood, fighting disease, skin,general health

Vitamin DChemical name: Cholecalciferol

Needed for: bones, teeth, nerves,heart, others general health

Vitamin EChemical name: Tocopherol

Needed for: blood, cellprocesses, muscles, nerves,general health

Vitamin KChemical name: Phylloquinone

Needed for: blood clotting,general health

Fats are used for bothbuilding and energy.

• Broken down by digestion into smaller, simpler pieces, called lipids.

• Foods with plenty of fats areusually fatty plant parts; includingred meats; oily fish; eggs, milk,cheese, and other dairy products;and certain foods like avocados,olives, and peanuts.

• Taken in and used both forbuilding parts, such as nerves,making and repairing parts ofmicroscopic cells, and asenergy that carbohydrates arelacking.

• Too much fat from animalsources (fatty red meats andprocessed foods, like burgersand salami) is linked tovarious health problems, suchas heart disease and highblood pressure.

Carbohydrates are “energy foods.”

• Broken down by digestion intosmaller, simpler pieces, such assugars.

• Taken in and used as the body’smain source of energy, calledglucose or blood sugar, for the lifeprocesses of all its microscopic cells.

• Also used for all musclemovements from heartbeat andbreathing to fast running.

• Foods with plenty of carbohydratesare starchy or sweet, such as rice,wheat, barley, and other grains.Products made from these arepasta and bread. There are alsomany “starchy” vegetables, likepotatoes and corn, and manysweet fruits like bananas andstrawberries, as well as sugaryitems like candy and chocolate.

CARBOHYDRATES

FATS AND OILS

FIBER

• Needed for various bodyprocesses to work, stay healthy,and ward off disease.

• Most are needed in small amounts,fractions of a gram per day.

• Have chemical names and alsoletters like A and B.

• The body can store somevitamins, but needs regularsupplies of others.

• Eating a wide range of foods,especially fresh fruits andvegetables, should provide all the body’s needs.

• Needed for various bodyprocesses to work, stayhealthy, and ward off disease.

• Most are needed in smallamounts, fractions of a gramper day.

• Most are simple chemicalsubstances, like iron, calcium,and sodium.

• The body can store someminerals but needs regularsupplies of others.

• Eating a wide range of foods,especially fresh fruits andvegetables, should provide all the body’s needs.

MINERALS

For an average adult with atypical office job, daily needsare:

Carbohydrates 300 grams (including 25 grams or more of fiber)

Proteins 50 grams

Fats 60 grams(mostly from plant sources)

Vitamins, examples:Vitamin C 0.06 gramVitamin K 0.00008 gram

Minerals, examples:Calcium 1 gramIron 0.018 gramChloride 3.4 grams

DAILY NEEDS

FOOD AND NUTRIENTS

Food can be divided into groups.This can help us plan a

balanced diet.

Yellow: meat and fishGreen: grainsRed: fruit and vegetablesBlue: dairy productsOrange: sugary foods

We should eat foods from eachof these groups in order to stayhealthy. We should choose moregrains, fruit, and vegetables,and eat less sugary food.

DIFFERENT SORTS OF FOOD Foods rich in protein are

sometimes called buildingfoods, as they help to buildour body parts.

• Broken down by digestion intosmaller, simpler pieces calledamino acids.

• Amino acids are taken in andbuilt into the body’s ownproteins that make up the mainstructure of muscles, bones,skin, and most other parts.

• Foods with plenty of proteininclude all kinds of meats;poultry like chicken, fish, andeggs; dairy products like milkand cheese; and some plantfoods like nuts, soybeans, andother beans and peas.

PROTEINS

“Five-a-day” means five helpings,portions, or servings of freshfruits or vegetables each day.

This should provide the body withenough of all the vitamins andminerals, as well as some energy and plenty of fiber.

MINERALC H A R T

IronNeeded for: red blood cells, skin,muscles, resisting stress, fightingdisease

CalciumNeeded for: bones, teeth, nerves,heartbeat, blood clotting, kidneys

SodiumNeeded for: nerves and nervesignals, digestion, blood, chemicalprocesses inside cells, kidneys

MagnesiumNeeded for: heartbeat and rhythm,energy use

IodineNeeded for: overall speed of body’schemical processes, making thyroidhormone

ZincNeeded for: healthy immunesystem, wound healing, maintainingsenses of smell and taste

Dairy products such as cheeseand sour cream are a good

source of protein.

Drinking a glass of fresh fruitjuice counts as one portion of

your “five-a-day” target.

Snacking on fresh fruits andvegetables will help to meet your

body’s vitamin requirements.

Bread is made from wheat, agood source of carbohydrates.

Fat is an importantpart of our diet,

but we should getmost of what weneed from plantsources, such as

olive oil.

Fresh fruit and vegetables are agood source of fiber, particularly

if the the skins are eaten as well.

VITAMINS

FIVE-A-DAY GUIDE

42

The body can’t digest food with just its digestive tract. The body also

needs the liver and pancreas. These are next to the stomach and they

are digestive glands, which means they make powerful substances to

break down food in the intestines. Together with the digestive tract, the liver

and pancreas make up the whole digestive system.


• It is 3.1 in. long and 1.1in.wide.


• The gall bladder can hold up to 1.6 fl. oz. of bile.

• After a meal, bile pours fromthe liver along the main bileduct, and from the gallbladder along the cystic ductinto the small intestine.

• Bile helps to digest the fatsand oils in foods.

• The liver makes up to twopints of bile each day.

The liver has more than 500known tasks in the body, andprobably more that haven’tyet been discovered. Some ofthe main ones are:

• Breaking down nutrients and other substances from digestionbrought direct to the liver from the small intestine.



• If levels of blood sugar are toolow, changing body starch backinto blood sugar and releasingit.


• Breaking down toxins andpossibly harmful substances,like alcohol and poisons.

• Helping to control the amount of water in blood

and body tissues.

• If levels of blood sugar are toohigh, changing this into bodystarch and storing it.

THE LIVER’S TASKS




• The heat from the liver isn’twasted. Blood spreads the heatall around the body.

WARM LIVER

See pages 34–35 for information on the CIRCULATORY SYSTEM.

LIVER AND PANCREAS



WHERE IN THE BODY?

WHEN THINGSGO WRONG

Alcohol is a toxins thattheliver breaks down and makes

harmless. Too much alcoholcan overload the liver and

cause a serious disease called cirrhosis.


liver

pancreas

gall bladder

4342

The body can’t digest food with just its digestive tract. The body also

needs the liver and pancreas. These are next to the stomach and they

are digestive glands, which means they make powerful substances to

break down food in the intestines. Together with the digestive tract, the liver

and pancreas make up the whole digestive system.

• Most body parts are supplied withblood flowing along one or a fewmain arteries.

• The liver has a main artery, thehepatic artery.

• The liver also has a second andmuch greater blood supply.

• This comes along a vessel calledthe hepatic portal vein.

• The hepatic portal vein is the only main vein that does not take blood straight back to the heart.

• It runs from the intestines to the liver, bringing blood full ofnutrients from digestion.

W H A T I S T H E L I V E R ?

The liver is the largestsingle organ inside thebody.

• Wedge-shaped, dark red in color.

• Typical weight 3.3 lbs.

• Depth at widest part on right side6 in.

• Has a larger right lobe andsmaller left lobe.

• Lobes separated by a stronglayer, the falciform ligament.


• It is 3.1 in. long and 1.1in.wide.


• The gall bladder can hold up to 1.6 fl. oz. of bile.

• After a meal, bile pours fromthe liver along the main bileduct, and from the gallbladder along the cystic ductinto the small intestine.

• Bile helps to digest the fatsand oils in foods.

• The liver makes up to twopints of bile each day.

The liver has more than 500known tasks in the body, andprobably more that haven’tyet been discovered. Some ofthe main ones are:

• Breaking down nutrients and other substances from digestionbrought direct to the liver from the small intestine.



• If levels of blood sugar are toolow, changing body starch backinto blood sugar and releasingit.


• Breaking down toxins andpossibly harmful substances,like alcohol and poisons.

• Helping to control the amount of water in blood

and body tissues.

• If levels of blood sugar are toohigh, changing this into bodystarch and storing it.

THE LIVER’S TASKS

Most babies and youngchildren have bigabdomens. This is partlybecause their liver ismuch larger in proportionto the body’s overallsize, than the liver of anadult.

• An adult liver is usually 1⁄40

of total body weight.

• A baby’s liver is nearer 1⁄20

of total body weight.

• Pancreas has two main jobs.

• One is to make hormones.

• The other is to makedigestive chemicals calledpancreatic juices.

• These juices contain about15 powerful enzymes thatbreak apart many substancesin foods, including proteins,carbohydrates, and fats.

• Pancreas makes about 3pints of digestive juices daily.

• During a meal, these passalong the pancreatic duct tubesinto the small intestine todigest foods there.

HOW THEPANCREAS WORKS




• The heat from the liver isn’twasted. Blood spreads the heatall around the body.

Fatty foods, such as fries, are broken apart by enzymes

made in the pancreas.

WARM LIVER

See pages 34–35 for information on the CIRCULATORY SYSTEM.

LIVER AND PANCREAS



WHERE IN THE BODY?

W H A T I S T H EPANCREAS?

The pancreas is a long,slim, wedge-shaped organ.

• It is soft, greyish-pink in color.• Typical weight 3.5 oz.

• Typical length 6 in.

• Has three main parts: head(wide end), body (middle) andtail (tapering end).

• See pages 36–37 forinformation on the BLOOD.

Babies and toddlers often have a tummy that sticksout, but it’s not thestomach that causes thisshape, it’s their liver.

• See page 52 forinformation on hormones.

One of the liver’s main functions is to break down nutrients forthe body. This means the liver has a unique blood supply.

A yellowish tinge to the skin and eyes is known asjaundice. It is often a sign ofliver trouble.

Usually, the liver breaks down old red blood cells and gets rid of thecoloring substance in bile fluid. If something goes wrong, the coloringsubstance builds up in blood and skinand causes jaundice.Hepatitis, an infection of the liver, cancause jaundice.

WHEN THINGSGO WRONG

Alcohol is a toxins thattheliver breaks down and makes

harmless. Too much alcoholcan overload the liver and

cause a serious disease called cirrhosis.


BABY LIVER

UNUSUAL SUPPLY

liver

liver

pancreas

liver

pancreas

gall bladder

• See pages 40–41 forinformation on the diet.

44

Your body makes wastes and unwanted substances that it must

remove. Some of this waste comes out of the end of the digestive

tract and is called solid waste. The other main kind is liquid waste,

called urine. Urine is created a very different way than solid waste. It is

made, not from digestive leftovers, but by filtering the blood.

Cortex Outer layer, formed mainly ofmicroscopic blood vessels from the filtering units, called nephrons.

MedullaInner layer, formed mainly from the tiny tubes of the nephrons.

Renal pelvis Space in the middle of the kidneywhere urine collects.

MAIN PARTS OF THE KIDNEY

• The right kidney is usually about0.4–0.6 in. lower than the left one.

• Each kidney is shaped like a bean witha slight indent on one side.

• Average kidney measurements are 4.3 in. high, 2.3 in. wide, and 1.1 in. from front to back.

• In a woman, the typical weight of thekidneys is 4.5–4.9 ounces.

• In a man, the typical weight is 4.9–5.2 ounces.

The parts of the urinary systemare inside the lower body orabdomen. The kidneys are atthe upper rear, on either sideof the backbone behind the

lower ribs. The bladder is thelowest part of the abdomen,

between the hips.

WHERE IN THE BODY?

Each kidney contains aboutone million microscopic filters,called nephrons.• Each nephron begins with a tiny

tangle or knot of the smallestblood vessels, called capillaries,known as the glomerulus.

• Waste substances and watersqueeze out of the glomerulusinto a cup-shaped part around it,called Bowman’s capsule.

• The wastes and water then flowthrough a microscopic tube, therenal tubule, where some water,minerals, and salts are takenback into the blood.

• All the tiny tubules of all thenephrons in one kidney,straightened out and joined endto end, would stretch 62 miles.

• The end result is urine, which is mostly water containingdissolved wastes like urea andammonia.

The kidneys’ huge blood supply can beseen by the size of the renal arteries(red) and veins (blue). The pale uretertubes lead down to the bladder.

The work of the kidney takesplace in the nephrons.

KIDNEYS ANDURINARY SYSTEM

KIDNEY MICROFILTERS

• See pages 38–39 for information on DIGESTION.

KIDNEYS – SIZE AND SHAPE

kidney kidney

bladder

glomerulus

Bowman’s capsule

45

B L O O D T OU R I N E

The kidneys receive moreblood, for their size, thanany other body part.

Amount of blood• Each minute at rest, the

kidneys receive 2.5 pints of blood.

• This is about one-fifth of allthe blood pumped out by the heart.

Quick flow • This blood flows quickly

through the kidneys, so they don’t actually contain one-fifth of all the body’s blood.

• Over 24 hours, all the bloodin the body passes throughthe kidneys more than 300times.

Amount of urine• From this blood is filtered,

on an average day, about 3 pints of urine.

Variation of amount• However, the amount of urine

varies according to how muchwater is taken into the bodyby food and drink.

• The amount of urine alsovaries according to how muchwater is lost in hot conditionsas sweat.

Hot and cold• On a hot day with few drinks,

urine volume may be lessthan 2 pints.

• On a cold day with manydrinks, urine volume may be more than 10.5 pints.

• The urethra, which takes urinefrom the bladder to the outside,is different in females and males.

• This is because in males, theurethra is part of the reproductivesystem as well as the urinarysystem.

• In females, the urethra is 1.5 in.long and 0.23 in. across.

• In males it is 7 in. long and runs inside the penis.

FEMALE AND MALEKidneysFilter the blood to make waste liquid,known as urine.

UretersTubes about 10–12 in. long thatcarry urine from the kidneys to thebladder.

BladderCorrectly called the urinary bladder,it stores urine until it is “convenient”to get rid of it.

UrethraTube that carries urine from thebladder to the outside.

MAIN URINARY PARTS

When empty, the bladder is pear-shaped and not much bigger than a thumb. It gradually stretches andfills with urine until it isemptied.

• We can tell how much urine isinside the bladder by how muchwe need to urinate.

• 8.4–10 fl. oz. of urine (aboutthe amount in a coffee mug) –slight urge to release the urine byurination.

• 13.5–16.9 fl. oz. – strongerurge to urinate.

• 16.9–19.2 fl.oz. – desperateurge to urinate.

Bacteria can infect the bladder,causing cystitis. Symptomsinclude a burning sensationduring urination and an urgentneed to empty the bladder,although little urine comes out.

Men and women have differentsystems for taking urine to theoutside of the body.

When you eat lots of meat, yoururine gets darker. This is becauseyour body makes urea, whichgives urine its color, from protein.

MEAT EATER

• See pages 40–41 forinformation on the diet.

44

Your body makes wastes and unwanted substances that it must

remove. Some of this waste comes out of the end of the digestive

tract and is called solid waste. The other main kind is liquid waste,

called urine. Urine is created a very different way than solid waste. It is

made, not from digestive leftovers, but by filtering the blood.

Cortex Outer layer, formed mainly ofmicroscopic blood vessels from the filtering units, called nephrons.

MedullaInner layer, formed mainly from the tiny tubes of the nephrons.

Renal pelvis Space in the middle of the kidneywhere urine collects.

MAIN PARTS OF THE KIDNEY

• The right kidney is usually about0.4–0.6 in. lower than the left one.

• Each kidney is shaped like a bean witha slight indent on one side.

• Average kidney measurements are 4.3 in. high, 2.3 in. wide, and 1.1 in. from front to back.

• In a woman, the typical weight of thekidneys is 4.5–4.9 ounces.

• In a man, the typical weight is 4.9–5.2 ounces.

The parts of the urinary systemare inside the lower body orabdomen. The kidneys are atthe upper rear, on either sideof the backbone behind the

lower ribs. The bladder is thelowest part of the abdomen,

between the hips.

WHERE IN THE BODY?

Each kidney contains aboutone million microscopic filters,called nephrons.• Each nephron begins with a tiny

tangle or knot of the smallestblood vessels, called capillaries,known as the glomerulus.

• Waste substances and watersqueeze out of the glomerulusinto a cup-shaped part around it,called Bowman’s capsule.

• The wastes and water then flowthrough a microscopic tube, therenal tubule, where some water,minerals, and salts are takenback into the blood.

• All the tiny tubules of all thenephrons in one kidney,straightened out and joined endto end, would stretch 62 miles.

• The end result is urine, which is mostly water containingdissolved wastes like urea andammonia.

The kidneys’ huge blood supply can beseen by the size of the renal arteries(red) and veins (blue). The pale uretertubes lead down to the bladder.

The work of the kidney takesplace in the nephrons.

KIDNEYS ANDURINARY SYSTEM

KIDNEY MICROFILTERS

• See pages 38–39 for information on DIGESTION.

See pages 34–35 forinformation on the

CIRCULATORY SYSTEM.

KIDNEYS – SIZE AND SHAPE

BLADDER – THE NEED TO GO

• See pages 48–49for information on REPRODUCTION.

kidneykidney

bladder

ureter

ureter

kidney kidney

bladder

glomerulus

Bowman’s capsule

GENETIC FINGERPRINTING

46

Most children look like their parents. This is because parents pass on

their genes to their children. Genes are instructions for how a

human body grows, develops, maintains and repairs itself, and

usually keeps itself healthy. Instructions for building a mechanical machine

are usually written as words and drawn as diagrams. The genetic instructions

for building and running the human body are in the form of a chemical

substance, called DNA.

All human beings have the same overall set of genes.Tiny differences, in less than1 out of 500 genes, makeeach of us unique.

• The exact number of genes thathuman beings is still disputed.

• Scientists believe human beingshave somewhere between30,000 and 35,000 genes.

• Nearly all other living things havegenes formed of DNA, like humanbeings.

• Often, the same genes doing thesame jobs occur in very differentkinds of living things.

• The more similar living things areto us, the more similar the sets of genes.

• A chimp has 98 of every 100genes in common with humanbeings.

• A fruit fly has 44 of every 100genes in comman with humanbeings.

• There are 46 lengths of DNA ineach cell’s control center, calledthe nucleus.

• Each length is tightly wound intoa shorter, thicker item, called achromosome.

• The chromosomes are not alldifferent, they are in 23 pairs.

• One chromosome from each paircame from the mother, and theother one from the father.

• Each time a cell divides as part of growth and normal bodymaintenance, all thechromosomes are copied.

• So each of the two resulting cellshas the complete set of 23 pairs.

• All 46 pieces of DNA in thechromosomes from a single cell,straightened out and joinedtogether, would stretch almost6.5 feet.

• If the same was done to all theDNA in the body, it would stretchfrom the Earth to the Sun andback 100 times!

CHROMOSOMES

GENES

Genes, in the form of thechemical DNA, are present in

almost all the microscopic cells inthe body. Only a few cell types,like red blood cells, lack them.

DNA is deoxyribonucleic acid.It is a chemical substanceshaped like two ladders heldand twisted like a corkscrew,called a double helix.

• DNA contains four kinds ofchemical sub-units called bases,named adenine (A), thymine(T), guanine (G), and cytosine(C).

• Like words in a sentence, thesebases are in a certain orderalong DNA.

• The order of the bases is thegenetic code carrying thegenetic instructions.

• In the full set of DNA there are3,200 million sets of bases.

• This full set of DNA containing all the genes for the humanbody is called the humangenome.

The genes that make a mouse are almost the same as those thatmake a person. Out of every 100 genes, a mouse has 92 that are

the same as ours.

DNA

GENES IN LIVING THINGS

WHERE IN THE BODY?

47

W H A T A R EGENES?

A gene is a portion of DNAcontaining the chemicalcode for making a part ofthe body or instructing howthat part works.

For example, the gene for eyecolor tells the body how to make the colored substance, called pigment, for the iris.

Number• The human body has a total of

about 30,000 genes.

• Sometimes, several genes worktogether to control one feature.

Instructions for appearanceGenes contain the information forskin color, hair color and type,overall adult height, ear lobe shape,and many other features of thebody.

Instructions for processesGenes also control how the body’schemical processes, like digestingfood, work.

Police procedures have beenrevolutionised since reliableDNA fingerprinting has beenavailable.

• Small pieces of DNA, forexample, from the white bloodcells in a tiny speck of blood, canbe copied millions of times.

• This is done by a laboratoryprocess, called polymerase chainreaction, PCR.

• PCR gives enough DNA for testingto look at various sets orsequences of genes.

• The main testing method is calledgel electrophoresis.

• The results are flat layers of ajelly-like substance containingdark bands, like a bar code.

• The sequence of bands gives a“genetic fingerprint.”

• If two samples of DNA matchexactly, the chances are millionsto one that they came from thesame body.

• Each gene can exist in severalforms, called alleles.

• The blue allele for the eye colorgene tells the body how to makeblue coloring substance for the iris.

• The brown allele tells the bodyhow to make brown coloringsubstance for the iris.

• As mentioned above, each personhas two copies of a gene, oneinherited from the mother, onefrom the father.

• A person with two alleles forbrown eyes has brown eyes.

• A person with two alleles for blueeyes has blue eyes.

• If a person has one allele for blueeyes and one for brown, the brownis stronger, called dominant, whilethe blue is weaker, calledrecessive, and the person hasbrown eyes.

• Many genes work in this way,with different alleles, which aredominant or recessive when puttogether.

In any family, the children usually look like at least one of theirparents. Sometimes, children look more like their grandparents,

because some characteristics do not show up in every generation.

W H A T A R ECLONES?

Usually, each person has aunique selection of genes.

The exception is identical twins,who have exactly the same genes.

Living things with exactly the samegenes are called clones.

Dolly the sheep is the most famousclone. Scientists took genes from anadult sheep and used them to createan identical copy.

The DNA from skin, hair, andblood can help the police intheir investigations. Geneticinformation can eliminate asuspect or help the police to

secure a conviction.

• See page 49 forinformation on making eggs

and sperm.

STRONG AND WEAK GENES

GENETIC FINGERPRINTING

46

Most children look like their parents. This is because parents pass on

their genes to their children. Genes are instructions for how a

human body grows, develops, maintains and repairs itself, and

usually keeps itself healthy. Instructions for building a mechanical machine

are usually written as words and drawn as diagrams. The genetic instructions

for building and running the human body are in the form of a chemical

substance, called DNA.

All human beings have the same overall set of genes.Tiny differences, in less than1 out of 500 genes, makeeach of us unique.

• The exact number of genes thathuman beings is still disputed.

• Scientists believe human beingshave somewhere between30,000 and 35,000 genes.

• Nearly all other living things havegenes formed of DNA, like humanbeings.

• Often, the same genes doing thesame jobs occur in very differentkinds of living things.

• The more similar living things areto us, the more similar the sets of genes.

• A chimp has 98 of every 100genes in common with humanbeings.

• A fruit fly has 44 of every 100genes in comman with humanbeings.

• There are 46 lengths of DNA ineach cell’s control center, calledthe nucleus.

• Each length is tightly wound intoa shorter, thicker item, called achromosome.

• The chromosomes are not alldifferent, they are in 23 pairs.

• One chromosome from each paircame from the mother, and theother one from the father.

• Each time a cell divides as part of growth and normal bodymaintenance, all thechromosomes are copied.

• So each of the two resulting cellshas the complete set of 23 pairs.

• All 46 pieces of DNA in thechromosomes from a single cell,straightened out and joinedtogether, would stretch almost6.5 feet.

• If the same was done to all theDNA in the body, it would stretchfrom the Earth to the Sun andback 100 times!

CHROMOSOMES

GENES

Genes, in the form of thechemical DNA, are present in

almost all the microscopic cells inthe body. Only a few cell types,like red blood cells, lack them.

DNA is deoxyribonucleic acid.It is a chemical substanceshaped like two ladders heldand twisted like a corkscrew,called a double helix.

• DNA contains four kinds ofchemical sub-units called bases,named adenine (A), thymine(T), guanine (G), and cytosine(C).

• Like words in a sentence, thesebases are in a certain orderalong DNA.

• The order of the bases is thegenetic code carrying thegenetic instructions.

• In the full set of DNA there are3,200 million sets of bases.

• This full set of DNA containing all the genes for the humanbody is called the humangenome.

The genes that make a mouse are almost the same as those thatmake a person. Out of every 100 genes, a mouse has 92 that are

the same as ours.

DNA

GENES IN LIVING THINGS

WHERE IN THE BODY?

For the first 8 weeks afterfertilization, the developingbaby is called an embryo.

Week 2 The embryo becomes the shape of aflat disc, surrounded by fluid, withinthe uterus lining. The disc lengthensand curls over at the edges.

Week 3 The curled-over disc becomes longerand larger at one end and beginsthe shape of the head and brain.Length is about 0.06 in.

Week 4

The embryo becomes C-shaped.Simple tubes start to make the heartand begin pulsating. Arms and legsbegin as small bulges on the body.Length is about 0.2 in.

Week 5 Head and brain grow rapidly. Innerorgans begin to fomr. Nose beginsto take shape. Length is about 0.31in.

Week 6

Heart and lungs almost formed,body becomes straighter. Eyes andears obvious. Length is about 0.47 in.

Week 7 Fingers and toes start to take shape.Neck becomes more visible. Tail shrinks. Length is about 0.6 in.

Week 8

Muscles and eyelids form, andthe tail has almost disappeared. All main body parts are present,even eyelids. Length is about0.67 in.

This picture shows the embryofloating in its amniotic bag of fluid.

Every human body starts as a fertilized egg cell, a tiny speck smaller

than the dot on this i. By the process of cell division, that single cell

becomes two, four, eight, and so on, building the human body. About

20 years later, by the time of adulthood, the body has 10 trillion cells of more

than 200 different kinds. It is a fascinating story of amazing growth and

development.

STAGES OF LIFE

Egg cell is joined or fertilizedby sperm cell, usually in theoviduct of the mother. Thegenes of egg and sperm (inthe form of DNA) cometogether and the geneticblueprint for a new body isformed.

24–36 hoursFertilized egg cell splits into twosmaller cells.

36–48 hoursEach of the two cells divide, formingfour cells.

2–3 daysCell division continues, forming a tinyball of more than a 20 cells movingslowly along the oviduct.

4 daysThe ball of more than 100 cells, calleda morula, reaches the inside of theuterus.

5 daysThe ball of hundreds of cells becomeshollow inside, called a blastocyst (earlyembryo).

6-7 days

The blastocyst, still only 0.003–0.007in. across, implants into the blood-richlining of the uterus.

The cells now take in nourishment fromthe lining and enlarge between divisions.

IN THE WOMB: WEEK ONE

IN THE WOMB: EMBRYO

The development of a babyinside the mother’s womb is

called pregnancy and lasts about9 months (average 266 daysfrom fertilization to birth).

Growth is fastest duringearly weeks in the womb andslows down towards birth.

• Speeds up slightly in first 2–3years after birth.

• Slows down toward the end ofchildhood.

• Sudden spurt during puberty,usually early teens.

• Slows down towards late teens.

• Full height usually by 20 years old.

50

GROWTH RATES

PREGNANCY

By their first birthday, most babieshave almost tripled their birthweight, from just over 7 to almost22 lbs. They have also grown inheight from about 21.6–30 in.Average times for movement andcoordination skills (although thereare wide variations)

4–8 weeksSmiles in response to faces. 2–4 monthsRaises head and shoulders whenlying on stomach.5–7 monthsRolls over from stomach to back. 6–8 monthsSits up perhaps with help, starts tomake babbling noises. 7–9 monthsBegins to try and feed itself, putsitems in mouth.8–10 monthsCrawls.10–12 monthsStands up with support.12–15 monthsWalks unaided.

51

Puberty is the time when thebody grows and developsrapidly from girl to woman or boy to man, and thereproductive (sex) parts start to work.

Puberty – girls• Can occur any time between 9

and 16 years of age. It usuallylasts 2–3 years.

• First signs include rapid growthand breasts begin to enlarge.

• Hair grows under arms andbetween legs, called pubic hair.

• Hips increase in width.

• Pads of fat laid down under skingive more rounded body outline.

• Voice deepens slightly.

• Menstrual cycle begins with firstperiod, called menarche.

Puberty – boys• Can occur any time between 11 and

17 years of age. It usually takes3–4 years.

• First signs include rapid growth inheight and hair growing underarms, between legs, and on face(moustache and beard).

• Shoulders increase in width.

• Muscle development increasesgiving more angular body outline.

• Voice deepens considerably or“breaks.”

• Reproductive organs enlarge andbegin to make sperm.

PUBERTY

NEW BABYFor the period between 8weeks after fertilization andbirth, the developing baby iscalled a fetus.

Month 3Finishing touches developed, includingfolds for fingernails and toenails.Eyelids closed. Head still very largecompared to body. Length 1.5 in.

Month 4Face looks much more human, firsthair grows on head. First bones beginto harden. Length 2.1 in.

Month 5Reproductive parts begin to take shape,showing if the fetus is a girl or body.Length 6 in.

Month 6Body becomes slimmer and is coveredwith fine hair, called lanugo. Fetuscan move arms and kick legs.

Month 7Body is lean and wrinkled. Fetus canswallow, eyes can detect light.

Month 8Body puts on fat. Nails grow to endsof fingers and toes.

Month 9Baby is chubbier and fully formed.Average weight at birth is 7.7–8.8lbs. Average length is 20–24 in.

IN THE WOMB: FETUS S I G N S O FAGING

Most people are at peakphysical fitness from early-20s to mid-30s.

• Most men run their lifetime bestbetween 27 and 29 years old.

• Most women run their lifetime bestbetween 29 and 31 years old.

• Most marathon runners performtheir best between 30 and 37years old.

Certain reactions and bodyprocesses begin to slowdown from the 40s insome people, but not untilthe 60s in others.Signs of aging:

• Wrinkled skin

• Graying or whitening of hair

• Hair loss

• Less muscle power

• More brittle bones

• Less flexible joints

• Senses become weaker

• The first sense to deteriorate isusually hearing, followed by sight.Touch and taste also becomeweaker, and then smell.

For the first 8 weeks afterfertilization, the developingbaby is called an embryo.

Week 2 The embryo becomes the shape of aflat disc, surrounded by fluid, withinthe uterus lining. The disc lengthensand curls over at the edges.

Week 3 The curled-over disc becomes longerand larger at one end and beginsthe shape of the head and brain.Length is about 0.06 in.

Week 4

The embryo becomes C-shaped.Simple tubes start to make the heartand begin pulsating. Arms and legsbegin as small bulges on the body.Length is about 0.2 in.

Week 5 Head and brain grow rapidly. Innerorgans begin to fomr. Nose beginsto take shape. Length is about 0.31in.

Week 6

Heart and lungs almost formed,body becomes straighter. Eyes andears obvious. Length is about 0.47 in.

Week 7 Fingers and toes start to take shape.Neck becomes more visible. Tail shrinks. Length is about 0.6 in.

Week 8

Muscles and eyelids form, andthe tail has almost disappeared. All main body parts are present,even eyelids. Length is about0.67 in.

This picture shows the embryofloating in its amniotic bag of fluid.

Every human body starts as a fertilized egg cell, a tiny speck smaller

than the dot on this i. By the process of cell division, that single cell

becomes two, four, eight, and so on, building the human body. About

20 years later, by the time of adulthood, the body has 10 trillion cells of more

than 200 different kinds. It is a fascinating story of amazing growth and

development.

STAGES OF LIFE

Egg cell is joined or fertilizedby sperm cell, usually in theoviduct of the mother. Thegenes of egg and sperm (inthe form of DNA) cometogether and the geneticblueprint for a new body isformed.

24–36 hoursFertilized egg cell splits into twosmaller cells.

36–48 hoursEach of the two cells divide, formingfour cells.

2–3 daysCell division continues, forming a tinyball of more than a 20 cells movingslowly along the oviduct.

4 daysThe ball of more than 100 cells, calleda morula, reaches the inside of theuterus.

5 daysThe ball of hundreds of cells becomeshollow inside, called a blastocyst (earlyembryo).

6-7 days

The blastocyst, still only 0.003–0.007in. across, implants into the blood-richlining of the uterus.

The cells now take in nourishment fromthe lining and enlarge between divisions.

IN THE WOMB: WEEK ONE

IN THE WOMB: EMBRYO

The development of a babyinside the mother’s womb is

called pregnancy and lasts about9 months (average 266 daysfrom fertilization to birth).

Growth is fastest duringearly weeks in the womb andslows down towards birth.

• Speeds up slightly in first 2–3years after birth.

• Slows down toward the end ofchildhood.

• Sudden spurt during puberty,usually early teens.

• Slows down towards late teens.

• Full height usually by 20 years old.

50

GROWTH RATES

PREGNANCY

THYMUS

52

Your brain controls your body. It tells muscles to pull, the lung

to breathe and the heart to beat. It does this by sending out tiny

electrical signals, called nerve messages. But the brain also controls

certain processes in another way, through natural body chemicals, called

hormones. These are made in hormone or endocrine glands. The hormones

travel around the body in the blood and affect how your body works. When you

are frightened and your heart pounds, that’s a hormone at work, called

adrenaline.

One of the smallest hormoneglands, but the mostimportant. It is controlled by the brain and sends outhormones that affect theworkings of other hormonalglands.

WhereBehind the eyes and below thecentral front of the brain, joined to itby a narrow stalk.

ShapeBean-like.

Size0.4 in. high, 0.47 in. wide, 0.3 in.thick, and weighs 0.017 lbs.

Hormones made About 10 including GH (growthhormone), ADH (antidiuretichormone), and TSH (thyroid-stimulating hormone).

Effects GH makes the whole body increasein size and development.

• ADH makes the kidneys take backmore water as they form urine.

• TSH makes the thyroid glandrelease more of its ownhormones.

WhereUnder the skin of the neck justbelow the voicebox, wrappedaround the upper windpipe.

ShapeLike a bowtie or butterfly.

Size3.1–3.9 in. wide, 1.1 in. high,0.8 in. thick, and weighs 0.8 lbs.

Hormones made Thyroxine (T4), tri-iodothyronine(T3), and calcitonin

Effects T4 and T3 make all the body’scells work faster so the whole bodychemistry, or metabolism, speedsup. Calcitonin lowers the level ofthe mineral calcium in the blood.

HORMONES

Hormone glands are scatteredthrough the central body, from

the head down through the neck into the lower abdomen.The reproductive organs, the

ovaries in women and the testesin men, are also hormonal

glands.

WHERE IN THE BODY?

Where4 glands, two embedded in eachside of the thyroid.

ShapeLike tiny eggs.

SizeEach are 0.22 in. high, 0.15 in.wide, 0.08 in. thick, and weighs0.0001 lbs.

Hormones made Parathormone

Effects Controls the level of calcium in blood.

PARATHYROIDS

• See page 40 forinformation on calcium.

Calcium is vital for our brains,muscles, and blood to workproperly, as well as buildingbones.

The pituitary gland helps children to grow properly. It is sometimescalled the master gland, because it controls several other glands.

• See pages 44–45 forinformation on the KIDNEYS

THYROID

PITUITARY

thyroid

53

F I G H T O R FLIGHT?

When the body is stressedor frightened and has to actfast, the adrenal glandsreleases their hormoneadrenaline, also calledepinephrine.

This helps it to get ready to face athreat and fight, or escape andflee from the danger in flight. Themain effects of adrenaline are:

Blood vessels• Widens blood vessels to muscles

and heart muscle.

Heart• Increases heart rate.

• Increases amount of bloodpumped by each heartbeat.

Breathing• Increases breathing rate.

• Widens airways in lungs allowingmore air with each breath.

Digestion• Decreases activity of inner

organs. like stomach andintestines.

Sugar levels• Raises level of glucose to provide

more energy for muscles.

Some body parts makehormones in addition to theirmain tasks.

StomachGastrin makes stomach lining releaseacid.

Heart Atriopeptin affects amounts of bodysalts and minerals and blood pressure.

Testes Testosterone gives men their malecharacteristics.

OvariesEstrogen and progesterone givewomen their female characteristics.

WhereIn the upper left abdomen, behindthe stomach.

ShapeLong, slim wedge-shaped.

Size6 in. long, weighs about 3.5 oz.

Hormones made Insulin and glucagon, made inabout one million tiny cells, calledislets, scattered through thepancreas.

Effects Insulin lowers level of glucose bymaking body cells take in more ofit. Glucagon raises the level.

PANCREAS

Our ancestors would have had to act fast if they saw

a potentially dangerouspredator. Adrenaline prepared

the body for the responsesthey would have made.

Where2 glands, one above each kidney.

ShapeLike a small pyramid on thekidney.

SizeEach is 2 in. high, 1.1 in. wide, 0.4 in. thick, and weighs 0.17 oz.

Hormones made Outer part, called the cortex,makes corticosteroid, or steroidhormones, including cortisol andaldosterone; inner part, calledthe medulla, makes adrenalineand similar hormones.

Effects Cortisol decreases the effects of stress and helps control blood sugar and body repair,aldosterone affects how the kidneys filter blood.

See the box on the right forinformation on adrenaline.

ADRENALS

WhereBehind the breastbone.

ShapeTwo joined sausage-like lobes.

SizeRelatively large in young children,thumb-sized and weighing up to0.7 oz., shrinks slightly duringadulthood.

Hormones made Thymosin, thymopoietin, and others

Effects Helps white blood cells to developtheir germ-attacking powers.

• See page 43 forinformation on the role thepancreas plays in digestion.

People with diabetes have a problem with the

hormone insulin. They mayhave to inject insulin into

their bodies.

The thymus gland in the chesthelps to make the white bloodcells which destroy germs.

• See pages 36–37 forinformation on the BLOOD.

The small intestine makes the hormone secretin, which tells thepancreas to release acid-neutralizing juices.

• See pages 48–49REPRODUCTION.

OTHER HORMONE-MAKING PARTS

THYMUS

52

Your brain controls your body. It tells muscles to pull, the lung

to breathe and the heart to beat. It does this by sending out tiny

electrical signals, called nerve messages. But the brain also controls

certain processes in another way, through natural body chemicals, called

hormones. These are made in hormone or endocrine glands. The hormones

travel around the body in the blood and affect how your body works. When you

are frightened and your heart pounds, that’s a hormone at work, called

adrenaline.

One of the smallest hormoneglands, but the mostimportant. It is controlled by the brain and sends outhormones that affect theworkings of other hormonalglands.

WhereBehind the eyes and below thecentral front of the brain, joined to itby a narrow stalk.

ShapeBean-like.

Size0.4 in. high, 0.47 in. wide, 0.3 in.thick, and weighs 0.017 lbs.

Hormones made About 10 including GH (growthhormone), ADH (antidiuretichormone), and TSH (thyroid-stimulating hormone).

Effects GH makes the whole body increasein size and development.

• ADH makes the kidneys take backmore water as they form urine.

• TSH makes the thyroid glandrelease more of its ownhormones.

WhereUnder the skin of the neck justbelow the voicebox, wrappedaround the upper windpipe.

ShapeLike a bowtie or butterfly.

Size3.1–3.9 in. wide, 1.1 in. high,0.8 in. thick, and weighs 0.8 lbs.

Hormones made Thyroxine (T4), tri-iodothyronine(T3), and calcitonin

Effects T4 and T3 make all the body’scells work faster so the whole bodychemistry, or metabolism, speedsup. Calcitonin lowers the level ofthe mineral calcium in the blood.

HORMONES

Hormone glands are scatteredthrough the central body, from

the head down through the neck into the lower abdomen.The reproductive organs, the

ovaries in women and the testesin men, are also hormonal

glands.

WHERE IN THE BODY?

Where4 glands, two embedded in eachside of the thyroid.

ShapeLike tiny eggs.

SizeEach are 0.22 in. high, 0.15 in.wide, 0.08 in. thick, and weighs0.0001 lbs.

Hormones made Parathormone

Effects Controls the level of calcium in blood.

PARATHYROIDS

• See page 40 forinformation on calcium.

Calcium is vital for our brains,muscles, and blood to workproperly, as well as buildingbones.

The pituitary gland helps children to grow properly. It is sometimescalled the master gland, because it controls several other glands.

• See pages 44–45 forinformation on the KIDNEYS

THYROID

PITUITARY

kidney kidney

spleen

small intestine

adrenal glands

thyroid

thymus gland

Viruses and bacteria arecontagious, which means they

spread between people.

54

Adenoids• Also called pharyngeal tonsils.

• Found at the rear of the nasalchamber in the uppermost throat.

• Consist of a gathering of smalllymph nodes, called nodules.

• Help to kill germs in air breathed.

• Swell up when battling illness,causing problems with air flowthrough the nose, and may needremoval if this happens too often.

Tonsils

• Also called palatine tonsils.

• Found at the sides of the throat,just below and on either side ofthe soft palate (rear of the roof ofthe mouth).


• Help to kill germs in air breathed,food, and drink.

• Swell up when battling illness,causing a sore throat.

• Tonsils may need removal if thishappens too often.

Spleen

• Behind and above the left kidney.

• Largest collection of lymph tissuein the body.

• Length about 4.7 in. (the size ofa clenched fist).

• Weight about 5.2 oz., but can behalf or twice this according toblood content and body’s state ofhealth.

There are about 500 lymphnodes all over the body.

• The larger ones are in the neck,armpits, chest, central abdomenand groin. There are others inthe crook of the elbow and theback of the knee.

• Most are shaped like balls,beans, or pears.

• Smallest ones less than 0.04 in.across, larger ones 0.6–.78 in.

• Contain mainly various kinds ofwhite blood cells.

• Can double in size when fightingillness.

• Lymph flows into each alongseveral afferent lymph vessels.

• Lymph flows away from eachalong one efferent vessel.

LYMPH NODES

SPECIALIST LYMPH PARTS

LYMPH ANDIMMUNE SYSTEMS

Lymph nodes and vessels arefound in most body parts,

especially in the neck, armpits,chest, central abdomen, andgroin. They are also in the

adenoids at the rear of the nasalchamber, the tonsils in the

throat, the spleen behind the leftkidney, and the thymus gland

behind the breastbone.

WHERE IN THE BODY?

Lymph fluid is usually paleor milky in colour.

• The average amount in the human body is 2–4.2 fl.oz.

• Contains mainly water, dissolvednutrients, and disease-fightingwhite blood cells and theantibodies they make.

• Forms from fluid that oozes outof and between cells andcollects inside and betweentissues.

• Flows slowly along smallerlymph vessels, which join toform larger ones.

• The fluid has no pump of itsown but moves by general bodypressure and the massagingeffect of muscles andmovements.

• Flows through lymph nodes on its journey.

• Lymph network gradually gatherslymph into two main lymphvessels of ducts in the chest.

• These are the right lymphaticduct and the thoracic duct.

• These ducts join the right andleft subclavian veins wherelymph joins the blood.

LYMPH FLUID

A typical lymph nodecontains lymph fluid and

white blood cells.

Red, sore, swollen tonsils are a sign of tonsillitis.

The dark-red spleen storesblood, recycles old red bloodcells, and makes new white

cells.

• See page 30–31 for information on the airways.

When people are ill, their glands often swell, especially in the neck,

armpits, and groin. But these are not really glands. They are

called lymph nodes, and they are part of the lymphatic system.

This system is the body’s alternative circulation method. Like blood, lymph

fluid flows around the body in tubes, called lymph vessels. Also like blood, it

carries nutrients to many parts and collects waste. It is closely linked to the

immune system, which specializes in attacking germs and fighting disease.

spleen

55

T Y P E S O FIMMUNITYThe body becomes immuneto illnesses in several ways.

Innate or native immunityAlready in the body.

Acquired immunity Occurs after exposure to antigens,for example, on the surface of atype of germ.

Natural acquired immunity Happens when the body catches thegerm naturally.

Artificial acquired immunity When an altered form of the germor its products is put into the bodyspecifically by vaccination.

Active immunity When the body makes its ownantigens.

Passive immunity When ready-made antibodies areput into the body.

Lymphocytes are one of the main kinds of whiteblood cells.

The healthy body contains about2 trillion lymphocytes. They aremade in bone marrow. There aretwo main kinds, B-cells and T-cells.

T-cell lymphocytes• T-cell lymphocytes are processed

or ‘trained’ in the thymus gland.

• T-cell lymphocytes kill “foreign”invading cells, like bacteria.

• T-cell lymphocytes also encourageB-cells to make antibodies.

• T-cell lymphocytes alsoencourage white cells, calledmacrophages, to engulf invadingmicrobes.

B-cell lymphocytes• B-cell lymphocytes respond the

chemical messages from T-cellymphocytes.

• B-cell lymphocytes areencouraged into activity by T-cells.

• B-cells change into plasma cellswhich make defensivesubstances, called antibodies.

• Different antibodies are made inresponse to different antigens,which are “foreign” substances on various invading microbes ormade by them.

• Antibodies travel in the bloodand lymph fluid.

• Antibodies join to antigens anddestroy them.

The immune system involvesthe lymph and blood systemsand also many other bodyparts.

• Based on white blood cells ofvarious kinds.

• Defends against harmfulsubstances, like toxins or poisons.

• Also protects the body againstinvasion by germs such asbacteria, viruses and microscopicparasites, called protists orprotozoans.

• Helps to clean away debris fromnormal body maintenance, as oldcells die and break down.

IMMUNE SYSTEM

MAIN DEFENDERS – LYMPHOCYTES

We are exposed to manygerms in our every day life.As we grow up, our bodiesgain immunity to most ofgerms naturally. There areonly a few diseases we

need to be protected fromartificially, through

immunizations.

IMMUNITYOnce we have caught anillness and fought theinfection, we have immunityto the germ in the future.

• After the body catches aninfection, especially by a virusgerm, white cells, calledmemory cells, “remember” thetype of virus.

• If the germ invades again later, the immune system canrecognize and fight it right awayand usually defeat it quickly.

• This is called being resistant orimmune to that particular germ.

• See page 16 for information on BONE MARROW and page 36–37 for information on BLOOD.

When we catch a cold, our immune system begins fighting it immediately. Colds usually last only a few days.

Viruses and bacteria arecontagious, which means they

spread between people.

54

Adenoids• Also called pharyngeal tonsils.

• Found at the rear of the nasalchamber in the uppermost throat.


• Help to kill germs in air breathed.

• Swell up when battling illness,causing problems with air flowthrough the nose, and may needremoval if this happens too often.

Tonsils

• Also called palatine tonsils.

• Found at the sides of the throat,just below and on either side ofthe soft palate (rear of the roof ofthe mouth).


• Help to kill germs in air breathed,food, and drink.

• Swell up when battling illness,causing a sore throat.

• Tonsils may need removal if thishappens too often.

Spleen

• Behind and above the left kidney.

• Largest collection of lymph tissuein the body.

• Length about 4.7 in. (the size ofa clenched fist).

• Weight about 5.2 oz., but can behalf or twice this according toblood content and body’s state ofhealth.

There are about 500 lymphnodes all over the body.

• The larger ones are in the neck,armpits, chest, central abdomenand groin. There are others inthe crook of the elbow and theback of the knee.

• Most are shaped like balls,beans, or pears.

• Smallest ones less than 0.04 in.across, larger ones 0.6–.78 in.

• Contain mainly various kinds ofwhite blood cells.

• Can double in size when fightingillness.

• Lymph flows into each alongseveral afferent lymph vessels.

• Lymph flows away from eachalong one efferent vessel.

LYMPH NODES

SPECIALIST LYMPH PARTS

LYMPH ANDIMMUNE SYSTEMS

Lymph nodes and vessels arefound in most body parts,

especially in the neck, armpits,chest, central abdomen, andgroin. They are also in the

adenoids at the rear of the nasalchamber, the tonsils in the

throat, the spleen behind the leftkidney, and the thymus gland

behind the breastbone.

WHERE IN THE BODY?

Lymph fluid is usually paleor milky in colour.

• The average amount in the human body is 2–4.2 fl.oz.

• Contains mainly water, dissolvednutrients, and disease-fightingwhite blood cells and theantibodies they make.

• Forms from fluid that oozes outof and between cells andcollects inside and betweentissues.

• Flows slowly along smallerlymph vessels, which join toform larger ones.

• The fluid has no pump of itsown but moves by general bodypressure and the massagingeffect of muscles andmovements.

• Flows through lymph nodes on its journey.

• Lymph network gradually gatherslymph into two main lymphvessels of ducts in the chest.

• These are the right lymphaticduct and the thoracic duct.

• These ducts join the right andleft subclavian veins wherelymph joins the blood.

LYMPH FLUID

A typical lymph nodecontains lymph fluid and

white blood cells.

Red, sore, swollen tonsils are a sign of tonsillitis.

The dark-red spleen storesblood, recycles old red bloodcells, and makes new white

cells.

• See page 30–31 for information on the airways.

When people are ill, their glands often swell, especially in the neck,

armpits, and groin. But these are not really glands. They are

called lymph nodes, and they are part of the lymphatic system.

This system is the body’s alternative circulation method. Like blood, lymph

fluid flows around the body in tubes, called lymph vessels. Also like blood, it

carries nutrients to many parts and collects waste. It is closely linked to the

immune system, which specializes in attacking germs and fighting disease.

spleen

AnaestheticReduces or gets rid of sensations,including pain.

AnalgesicReduces pain.

Beta-blockerSlows heartbeat and makes it moreregular, lowers blood pressure.

BronchodilatorWidens, or dilates, the smallairways, called bronchioles, in thelungs.

CytotoxicDestroys cells, especially malignant or cancerous ones, in chemotherapy.

DiureticReduces water content of the bodyby increasing amount of urine.

ImmunosuppressiveReduces the actions of the body’simmune defense system. Forexample, so it does not reject anorgan transplanted from anotherperson.

SteriodsLarge group of medicines, includinghormones and substances, that helpto increase muscle size or reduce theaction of the immune defense system.

ThrombolyticDissolves blood clots.

Vasoconstrictor Makes the small artery blood vesselsnarrower.

Vasodilator Makes the small artery blood vesselswider.

Many drugs have a name thatbegins anti-. This shows whichproblem the drug fights against.

AntibioticDisables or destroys microbes,mainly bacteria.

AnticoagluantPrevents blood clotting.

AnticonvulsantLessens the risk of convulsions orseizures.

AntidepressantReduces the effects of depressiveillness by lifting mood.

AntiemeticReduces feelings of sickness or nausea.

AntifungalDisables or destroys fungal microbes.

AntihistamineUsed against allergic-type illnessessuch as hay fever, asthma, and foodallergy.

Anti-inflammatory Reducing inflammation (redness,swelling, soreness, and pain)

AntipyreticLowers fever, reduces bodytemperature.

AntisepticKills most kinds of germs, usuallyapplied to the skin.

AntitoxinMakes a poisonous or toxicsubstance harmless.

AntiviralDisables or destroys virus microbes.

MEDICAL DRUGS

TYPES OF MEDICINES

Any part of the body has thepotential to stop functioning as

well as it should.

WHERE IN THE BODY?

• Genetic problems that can be passed on from parents orbegin as a new case when genesare not copied correctly as cellsmultiply in the developing body.

• Congenital problems that arepresent at birth.

• Infections caused by invadingmicrobes.

• Infestations due to worms, fleas,and similar animals.

• Malnutrition, due to not enoughfood and/or foods which are notbalanced in their nutrients.

• Toxins or poisons from thesurroundings, such as in water.

• Physical harm by accidents andinjuries.

• Radiation, such as radioactivity,nuclear rays, and the sun’sharmful ultraviolet rays.

• Cancers, where cells multiply outof control and spread to invadeother body parts.

• Autoimmune problems, wherethe body’s immune defencesystem mistakenly attacks thebody (as in rheumatoid arthritis).

• Allergic disorders, where thebody’s immune defence systemmistakenly attacks harmlesssubstances, like plant pollen inhay fever.

• Metabolic conditions, when there is a problem with the inner processes of bodychemistry.

The symptoms of an illness are usually easy to tell, but it can bequite hard for doctors to diagnose the cause of a problem.

DISEASES AND MEDICINES

Most of the time, human beings are well. Nearly everyone gets the

occasional cold and cough. Some people have a few bigger health

problems, like an infection, such as chickenpox, or an injury, such

as a sprained joint or broken bone. A few people are ill quite often. However,

the basic rules for good health are the same: do not smoke, eat a nutritious

and balanced diet, get plenty of exercise and activity, and keep a positive

attitude.

56

MAJOR CAUSES OF ILLNESS AND DISEASE

57

M E D I C A LSPECIALISTSAnaesthetistGiving anaesthetics to removesensation and pain while patientis still conscious (localanaesthetic) or to make thepatient unconscious as well(general anaesthetic).

CardiologistHeart and main blood vessels.

DermatologistSkin, hair, and nails.

GynecologistFemale reproductive and urinaryorgans.

GeriatricsOld age and old age diseases.

HaematologistBlood and body fluids.

NeurologistBrain and nerves.

ObstetricianPregnancy and birth.

OncologistTumours, especially cancers andsimilar conditions.

OphthalmologistEyes.

Orthopaedic surgeonBones, joints, and the skeleton.

PaediatricianCare of children.

PathologistThe processes and changes ofdisease, such as laboratorystudies of samples.

PhysiotherapistUsing physical measures such asmassage, manipulation, exercise,and heat.

Primary Care PhysicianGeneral family heathcare.

PsychiatristMental and behavioral problems.

RadiologistDiagnoses with X-rays and scans.

Thoracic surgeon Chest, especially lungs andairways, also heart.

UrologistUrinary system of kidneys,bladder, and their tubes.

• Smallest known forms of life,often considered living andnonliving things.

• About half a million would fit onthis period.

• Invade the body’s ownmicroscopic cells.

• Take over these cells and makethem produce more copies of the virus.

• Viral infections include commoncolds, most types of flu(influenza), polio (poliomyelitis),skin warts, chickenpox, measles,mumps, rubella, yellow fever,most kinds of hepatitis, rabies,Ebola, and AIDS (due to HumanImmunodeficiency Virus, HIV).

• Are not affected by antibioticdrugs.

• Several viral infections can beprevented by vaccination to makethe body resistant or immune tothem, called immunization.

• Several kinds of harmfulmicrobes cause infectiousdiseases, or infections.

• They are known commonly as germs.

• Most get into the bodythrough air, in food or drink,or through wounds.

• When a harmful microbespreads by direct or personalcontact between people,rather than by indirect means,such as air or water, this isknown as a contagiousinfection.

• The time when the harmfulmicrobe multiplies inside thebody, but the person does notshow signs of illness, is theincubation period.

DISEASE-CAUSINGMICROBES

VIRUSES

MICROFUNGI• Each microfungi is a single cell.

• Belong to the fungus group,which includes mushrooms,toadstools, and yeasts.

• Often grow and spread onthe skin.

• Diseases include athlete’s foot,ringworm, and fungal nail andhair infections.

• Each bacteria is a single cell.

• Microscopic, about 100,000would fit inside this letter o.

• Different groups are known bytheir shapes, such as cocci (ballsor spheres), bacilli (rods orsausages), and spirochaetes(corkscrews).

• Many are disabled or killed byantibiotic drugs.

• Bacterial infections include manykinds of sore throat, skin boils,pertussis (whooping cough),tetanus, scarlet fever, mostkinds of cholera and dysentery,plague, diphtheria, Legionnaire’sdisease, many kinds ofbronchitis, most types of foodpoisoning, ear infections, andanthrax.

• Each protist is a single cell.

• Sometimes called parasites ormicroparasites.

• Most are microscopic, about1,000 would fit inside this o.

• More common in warmercountries.

• Diseases caused include malaria(plasmodium), sleeping sickness(trypanosome), Chagas’ disease(trypanosoma cruzi), and riverblindness (schistosomiasis).

BACTERIA PROTISTS (PROTOZOA)

Two bacteria, magnified50,000 times.

The disease malaria is causedby a protist. It is transmittedto humans through mosquitos.

• See page 55 for information on TYPES OF IMMUNITY.

Scientists can only treat thesymptoms of most viral

infections, not the virus itself.

AnaestheticReduces or gets rid of sensations,including pain.

AnalgesicReduces pain.

Beta-blockerSlows heartbeat and makes it moreregular, lowers blood pressure.

BronchodilatorWidens, or dilates, the smallairways, called bronchioles, in thelungs.

CytotoxicDestroys cells, especially malignant or cancerous ones, in chemotherapy.

DiureticReduces water content of the bodyby increasing amount of urine.

ImmunosuppressiveReduces the actions of the body’simmune defense system. Forexample, so it does not reject anorgan transplanted from anotherperson.

SteriodsLarge group of medicines, includinghormones and substances, that helpto increase muscle size or reduce theaction of the immune defense system.

ThrombolyticDissolves blood clots.

Vasoconstrictor Makes the small artery blood vesselsnarrower.

Vasodilator Makes the small artery blood vesselswider.

Many drugs have a name thatbegins anti-. This shows whichproblem the drug fights against.

AntibioticDisables or destroys microbes,mainly bacteria.

AnticoagluantPrevents blood clotting.

AnticonvulsantLessens the risk of convulsions orseizures.

AntidepressantReduces the effects of depressiveillness by lifting mood.

AntiemeticReduces feelings of sickness or nausea.

AntifungalDisables or destroys fungal microbes.

AntihistamineUsed against allergic-type illnessessuch as hay fever, asthma, and foodallergy.

Anti-inflammatory Reducing inflammation (redness,swelling, soreness, and pain)

AntipyreticLowers fever, reduces bodytemperature.

AntisepticKills most kinds of germs, usuallyapplied to the skin.

AntitoxinMakes a poisonous or toxicsubstance harmless.

AntiviralDisables or destroys virus microbes.

MEDICAL DRUGS

TYPES OF MEDICINES

Any part of the body has thepotential to stop functioning as

well as it should.

WHERE IN THE BODY?

• Genetic problems that can be passed on from parents orbegin as a new case when genesare not copied correctly as cellsmultiply in the developing body.

• Congenital problems that arepresent at birth.

• Infections caused by invadingmicrobes.

• Infestations due to worms, fleas,and similar animals.

• Malnutrition, due to not enoughfood and/or foods which are notbalanced in their nutrients.

• Toxins or poisons from thesurroundings, such as in water.

• Physical harm by accidents andinjuries.

• Radiation, such as radioactivity,nuclear rays, and the sun’sharmful ultraviolet rays.

• Cancers, where cells multiply outof control and spread to invadeother body parts.

• Autoimmune problems, wherethe body’s immune defencesystem mistakenly attacks thebody (as in rheumatoid arthritis).

• Allergic disorders, where thebody’s immune defence systemmistakenly attacks harmlesssubstances, like plant pollen inhay fever.

• Metabolic conditions, when there is a problem with the inner processes of bodychemistry.

The symptoms of an illness are usually easy to tell, but it can bequite hard for doctors to diagnose the cause of a problem.

DISEASES AND MEDICINES

Most of the time, human beings are well. Nearly everyone gets the

occasional cold and cough. Some people have a few bigger health

problems, like an infection, such as chickenpox, or an injury, such

as a sprained joint or broken bone. A few people are ill quite often. However,

the basic rules for good health are the same: do not smoke, eat a nutritious

and balanced diet, get plenty of exercise and activity, and keep a positive

attitude.

56

MAJOR CAUSES OF ILLNESS AND DISEASE

Abdomen The lower part of the main body or torso,below the chest, that mainlycontains digestive andexcretory organs, and infemales, reproductive parts.

Artery A blood vessel thatconveys blood away from theheart.

Axon The very long, thinpart of a nerve cell or neuron,also called a nerve fiber.

Bladder Bag-like sac orcontainer for storing fluids.The body has several,including the urinary bladder, often just called thebladder, and gall bladder.


Capillary The smallest typeof blood vessels, usually lessthan 0.02 in. long and toothin to see except through amicroscope.

Cardiac Having to do withthe heart.

Cartilage Tough, light,slightly bendy andcompressible bodysubstance, often calledgristle, that forms parts of the skeleton, such as theears and nose, and alsocovers the ends of bones in joints.

Cell The basic microscopic“building block” of the body,a single living unit, with mostcells being 1/1,000 in.across. The body containsover 10 trillion cells.


Cerebral Having to do withthe cerebrum, the largest part of the brain that forms itswrinkled domed shape.

Cerebrospinal fluid Liquidsurrounding the brain andspinal cord, to protect andcushion them as well ashelping provide nourishmentand taking away waste.


a cell, that can waveor bend, andperhaps sensesubstances, such as

the olfactory epitheliumof the nose and in the tastebuds on the tongue. (Plural:cilia.)


Collagen Tiny, tough, strongfibers found in body parts


Cortex The outer part orlayer of a body part, such as the renal cortex of thekidney or the cerebral cortex of the brain.

Cranium The upper domedpart of the skull that coversand protects the brain.

Cermis The inner layer ofskin, under the epidermis,that contains the touchsensors, hair follicles, andsweat glands.

DNA Deoxyribonucleic acid,the chemical substance that forms the geneticinformation, called genes.

Embryo The name for adeveloping human body,from fertilization as a single cell to eight weeks later.

Endocrine Having to dowith hormones and thehormonal system (seehormone).

Enzymes Substancesthat alter the speed of achemical change or reaction,usually speeding it up, butremain unchangedthemselves at the end of the reaction.


Excretory Having to dowith removing wastesubstances from the body.The main excretory system ismade up of the kidneys,bladder and their linkingtubes.


Fetus A developing humanbody, from eight weeks afterfertilization until birth.

Fovea The small area in theretina of the eye where visionis most detailed and clearest,due to the large number ofcone cells.

Gastric Having to do withthe stomach.

Gland A body part thatmakes a substance that itthen releases, such as thetear glands that make tearfluid for the eyes, and thesweat glands in the skin.

Glucose See bloodsugar.

Gustatory Having to dowith the tongue and taste.

Hepatic Having to do withthe liver.

Hormone A naturalchemical messenger thatcirculates in the blood andaffects how certain bodyparts work, helping thenervous system to control and coordinate all bodyprocesses.

Humor Old word used todescribe various body fluids,still used in some cases. Forexample, to describe thefluids inside the eye, thevitreous humor and aqueoushumor.


Integumentary Having todo with the skin and othercoverings, including nailsand hair.


Medulla The central regionof a body part, such as therenal medulla of the kidney,

GLOSSARY

58

GLOSSARYor the adrenal medulla of theadrenal gland.

Meninges Three thin layerscovering the brain and spinalcord, and also making andcontaining cerebrospinalfluid. They are known as thedura mater, arachnoid, andpia mater.

Meiosis Part of special typeof cell division, when thechromosomes are not copiedand only one set (not adouble-set) moves into each resulting cell.

Metabolism All of thebody’s thousands of chemicalprocesses, changes, andreactions, such as breakingapart blood sugar to releaseenergy, and building upamino acids into proteins.

Mineral A simple chemicalsubstance, usually a metalsuch as iron or calcium, or a salt-type chemical, such asphosphate, which the bodyneeds in small quantities fromfood to stay healthy.

Mitosis Part of normal cell division, when thechromosomes have beencopied and one full double-set moves into each resultingcell.

Motor nerve A nerve thatcarries messages from thebrain to a muscle, telling itwhen to contract, or to agland, telling it when torelease its content.

Mucus Thickish, sticky, slimysubstance made by manybody parts, often forprotection and lubrication,such as inside the nose andwithin the stomach.

Myo- Having to do withmuscles, such as myocardiumor heart muscle.

Nephron Microscopicfiltering unit in the kidney forcleaning the blood.Neuron A nerve cell, the

basic unit of the nervoussystem.

Olfactory Having to dowith the nose and smell.

Optic Having to do with theeye, especially the opticnerve carrying messagesfrom the eye to the brain.

Papillae Small bumps on abody part, such as the tongue.

Peripheral nerves Thebodywide network of nerves,excluding the central nervoussystem.

Peristalsis Wave-likecontractions of muscles in thewall of a body tube, such asthe small intestine, ureter(from kidney to bladder), or oviduct (from ovary towomb).

Pulmonary Having to dowith the lungs.

Renal Having to do with thekidneys.

Sebum Natural waxysubstance, made in sebaceousglands associated with hairfollicles, that keeps skinsupple and fairly waterproof.

Sensory nerve A nervethat carries messages to thebrain from a sense part, suchas the eye, the ear, the tinystretch sensors in musclesand joints, and the bloodpressure sensors in mainarteries.

Skeletal Having to do withthe skeleton.

System In the body, a set ofmajor parts and organs thatall work together to fulfil onemain task, such as therespiratory system, whichtransfers oxygen from theair around to the blood.

Tendon The string,fibrous, rope-like endof a muscle, where ittapers and joins toa bone.

Thoracic Having to do withthe chest, called the thorax.

Thrombosis The process ofblood going lumpy to form aclot, also known as athrombus.

Tissue A group of verysimilar cells all doing the same job, such as muscletissue, adipose, or fat tissue,epithelial (covering or lining)tissue, and connective tissue(joining and filling in gapsbetween other parts).

Valve A flap, pocket, orsimilar part that allows a substance to pass one waybut not the other.

Vein A blood vessel thatconveys blood toward theheart.

Vertebra A single bone ofthe row of bones called thebackbone, spine, or vertebralcolumn.

Villi Tiny finger-like objectsfrom the microscopic cells invarious body parts, includingthe inner lining of the smallintestine.

Visceral Having to do withthe main parts or organsinside the abdomen (thelower part of the torso),mainly the stomach,intestines, kidneys, bladder,and in females, reproductiveparts.

Vitamin Substance neededin fairly small amounts fromfood for the body to workwell and stay healthy.

59

Abdomen The lower part of the main body or torso,below the chest, that mainlycontains digestive andexcretory organs, and infemales, reproductive parts.

Artery A blood vessel thatconveys blood away from theheart.

Axon The very long, thinpart of a nerve cell or neuron,also called a nerve fiber.

Bladder Bag-like sac orcontainer for storing fluids.The body has several,including the urinary bladder, often just called thebladder, and gall bladder.


Capillary The smallest typeof blood vessels, usually lessthan 0.02 in. long and toothin to see except through amicroscope.

Cardiac Having to do withthe heart.

Cartilage Tough, light,slightly bendy andcompressible bodysubstance, often calledgristle, that forms parts of the skeleton, such as theears and nose, and alsocovers the ends of bones in joints.

Cell The basic microscopic“building block” of the body,a single living unit, with mostcells being 1/1,000 in.across. The body containsover 10 trillion cells.


Cerebral Having to do withthe cerebrum, the largest part of the brain that forms itswrinkled domed shape.

Cerebrospinal fluid Liquidsurrounding the brain andspinal cord, to protect andcushion them as well ashelping provide nourishmentand taking away waste.


a cell, that can waveor bend, andperhaps sensesubstances, such as

the olfactory epitheliumof the nose and in the tastebuds on the tongue. (Plural:cilia.)


Collagen Tiny, tough, strongfibers found in body parts


Cortex The outer part orlayer of a body part, such as the renal cortex of thekidney or the cerebral cortex of the brain.

Cranium The upper domedpart of the skull that coversand protects the brain.

Cermis The inner layer ofskin, under the epidermis,that contains the touchsensors, hair follicles, andsweat glands.

DNA Deoxyribonucleic acid,the chemical substance that forms the geneticinformation, called genes.

Embryo The name for adeveloping human body,from fertilization as a single cell to eight weeks later.

Endocrine Having to dowith hormones and thehormonal system (seehormone).

Enzymes Substancesthat alter the speed of achemical change or reaction,usually speeding it up, butremain unchangedthemselves at the end of the reaction.


Excretory Having to dowith removing wastesubstances from the body.The main excretory system ismade up of the kidneys,bladder and their linkingtubes.


Fetus A developing humanbody, from eight weeks afterfertilization until birth.

Fovea The small area in theretina of the eye where visionis most detailed and clearest,due to the large number ofcone cells.

Gastric Having to do withthe stomach.

Gland A body part thatmakes a substance that itthen releases, such as thetear glands that make tearfluid for the eyes, and thesweat glands in the skin.

Glucose See bloodsugar.

Gustatory Having to dowith the tongue and taste.

Hepatic Having to do withthe liver.

Hormone A naturalchemical messenger thatcirculates in the blood andaffects how certain bodyparts work, helping thenervous system to control and coordinate all bodyprocesses.

Humor Old word used todescribe various body fluids,still used in some cases. Forexample, to describe thefluids inside the eye, thevitreous humor and aqueoushumor.


Integumentary Having todo with the skin and othercoverings, including nailsand hair.


Medulla The central regionof a body part, such as therenal medulla of the kidney,

GLOSSARY

58

60



“Adam’s apple” 31dadenine 46aadenoids (pharyngeal


36b, 52b-d, 53c, 53dageing 51dalcohol 21d, 42a-caldosterone 53calleles 47a-callergies 56b, 56c-dalveoli 31a-camino acids 41aammonia 44a-damniotic fluid 50a-danaesthetics 56a, 57danaesthetist 57danalgesics 56aankles 15dantiemetics 56banti-inflammatories 56bantibiotic drugs 56b, 57aantibodies 37d, 54b,


52c-dantifungal 56bantigens 55a-c, 55dantihistamine 56bantipyretic 56bantiseptic 56bantitoxin 56bantiviral 56b

anus 6-7c, 38a, 39a-canvil bone (incus) 24aaorta 33d, 34a-b,


33dappendix 38a,

39daqueous humor 23a-c

arms 15darteries 20a, 33a-c,

34, 35, 36a, 43b-c, 44b-d

arterioles 35a-c, 35d, 36b

artificial acquired immunity 55d





20b-c



36-7, 40a, 45dclotting 6-7b, 36c-d, 37d,



20a, 30b-d, 37d, 40c-d,42a-c, 53




37a-cbones 6-7a, 16-17, 40a,



20-1, 24c-d, 37a-b,52b-d












17dcells 6-7a, 40, 49a-c,

50b-dsee also named types of cell





The letters a, b, c, d following thepage number indicate the column(from left to right) in which theinformation may be found onthat page.

INDEX

61

INDEX

60



“Adam’s apple” 31dadenine 46aadenoids (pharyngeal


36b, 52b-d, 53c, 53dageing 51dalcohol 21d, 42a-caldosterone 53calleles 47a-callergies 56b, 56c-dalveoli 31a-camino acids 41aammonia 44a-damniotic fluid 50a-danaesthetics 56a, 57danaesthetist 57danalgesics 56aankles 15dantiemetics 56banti-inflammatories 56bantibiotic drugs 56b, 57aantibodies 37d, 54b,


52c-dantifungal 56bantigens 55a-c, 55dantihistamine 56bantipyretic 56bantiseptic 56bantitoxin 56bantiviral 56b

anus 6-7c, 38a, 39a-canvil bone (incus) 24aaorta 33d, 34a-b,


33dappendix 38a,

39daqueous humor 23a-c

arms 15darteries 20a, 33a-c,

34, 35, 36a, 43b-c, 44b-d

arterioles 35a-c, 35d, 36b

artificial acquired immunity 55d





20b-c



36-7, 40a, 45dclotting 6-7b, 36c-d, 37d,



20a, 30b-d, 37d, 40c-d,42a-c, 53




37a-cbones 6-7a, 16-17, 40a,



20-1, 24c-d, 37a-b,52b-d












17dcells 6-7a, 40, 49a-c,

50b-dsee also named types of cell





choking 31dchoroid 23a-cchromosomes 46b, 49a-ccilia 26c-dciliary muscle 23a-ccirculatory system see

cardiovascular systemcirrhosis 42a-cclones 47dclots see blood clottingcobalamin (Vitamin B12)

41dcocci 57acoccyx 14a-b, 15dcochlea 24a, 25a-ccollagen 9b, 16b-dcolon cancer 41b-ccolon (large intestine) 38b-

c, 39color 22b-dcones 22a, 22b-dcongenital problems 56c-dconjunctiva 23a-cconstipation 41b-cconvulsions 56bcornea 23a-ccoronary arteries 35a-ccortex, kidney 44acorticosteroid hormones

53ccortisol 53ccostal cartilage 15a-bcoughing 30bcranial nerves 18a, 19dcranium 14c-d, 15d, 17d,

20a

cruciate ligaments 17a-ccuticle 10b-dcystic duct 42dcystitis 45a-ccytosine 46acytotoxic 56a

Ddecibels 25ddendrites 19a-b, 19c,

20b-cdepression 56bdepressor labii muscle

12a-ddermatologist 57ddermis 9bdiabetes 53adiaphragm 30adigestive system 6-7c, 18b,

38-9, 40, 42b-d, 43a,47d

and adrenaline 53dand brain 21a-cdiscs 17ddisease 40a, 56-7diuretic 56aDNA (deoxyribonucleic

acid) 46, 47a-c, 50b-dDolly the sheep 47ddrugs 56bductus deferens (vas

deferens) 49a-c, 49dduodenum 39d

Eears 6-7c, 15a-b, 19d,

24-5egg cells 6-7b, 48, 49, 50ejaculation 49a-celastin 9bembryo 6-7b, 50emotions 21a-c, 26aendocrine (hormonal)

system 6-7c, 52a, 52b-denergy 12a, 16a, 20a,

38b-d, 40aenzymes 29d, 38b-d, 43aepidermis 9a, 10b-depididymis 49a-c, 49depidural anaesthetic 21a-bepiglottis cartilage 31depimysium 13a-cepinephrine see adrenalineepineurium 18c-deponychium 10b-derector pili muscle 11derythrocytes see red blood

cellsesophagus 6-7c, 38b-c,

39a-cestrogen 48a-d, 53a-ceye teeth 29ceyebrows 10a, 10b-d,

11a-beyelashes 10a, 10b-d,

11a-beyes 6-7c, 19d, 22-3,

47a-c, 47d

Fface, bones 15dfacial muscles 12afaeces 6-7c, 39b-cfallopian tubes (oviducts)

48b, 48c-d, 50b-dfascicles 13a-cfats 38b-d, 40, 42d, 43afatty tissue 9a-c, 36afemale sex organs 48afemur (thigh bone) 15a-c,

15d, 17cfever 56bfiber (roughage) 39b-c,

40b-d, 41b-cfibril 13a-cfingerprints 8c-d,

23a-bfixed joint 17dflavorants 26b-d,

27a-cflavors 27a-bfloaters 22afoetus 51a-bfolic acid (Vitamin

BF) 41dfollicles 9b, 11a-cfood 38b-d, 40-1

foot 15dforamen 16afovea 22b-dfrontalis muscle 12a-dfrown 12afungal microbes 56b

Ggall bladder 6-7c, 42dgastric artery 35a-cgastric juices 38b-d, 39a-cgastric vein 35a-cgastrin 53a-cgel electrophoresis 47a-cgenes 46a, 46b-d, 47a-c,

47d, 49a-csee also DNA

genetics 46-7, 56c-dgeriatrics 57dgerms 9d, 56bglands 6-7b, 8, 23, 29,

39, 42, 49, 52, 53, 54, 55

see also endocrinesystem; lymphaticsystem; named glands

glomerulus 44a-dglucagon 53aglucose see blood sugargluteus maximus muscle

13dglycogen 42a-cgravity 6-7c, 24a-dgrowth 50a, 50b-d, 52c-dguanine 46aguts 19d, 20agynecologist 57d

The letters a, b, c, d following thepage number indicate the column(from left to right) in which theinformation may be found onthat page.

INDEX

61

INDEX

62

Hhaematologist 57dhaemoglobin 37a-chair 6-7c, 8b-d, 9b, 10-11,

25a-chammer (malleus) bone

24ahands 15dhard palate 28dHaversian systems (osteons)

16ahay fever 56bhead 35a-chearing 24-5heart 6-7b, 19d, 20a, 32-

3, 34a-b, 35a-c, 53a-cand adrenaline 53dblood flow 37a-band brain 21a-csee also cardio-

heart disease 40c-dheart specialist 57dheartbeat 40a, 40c-d, 56ahepatic artery 35a-c, 43b-chepatic portal vein 43b-chepatic vein 35a-c

hepatitis 43ahinge joint 17dhips (pelvis) 15d, 17c, 17dhormonal (endocrine)

system 6-7a, 6-7b, 6-7c,52a, 52b-d

hormones 6-7c, 37d, 42-3,48a-d, 56a see also hormonal(endocrine) system

human genome 46ahygiene 29dhyoid bone 14ahypermetropia (long sight)

23chypodermis 9chypothalamus 21a-c

Iidentical twins 47dileum 39diliac artery 35a-ciliac vein 35a-cimmmunosuppressives 56aimmune system 6-7b, 6-7c,

40a, 54-5immunization 55d, 57b-cincus (anvil bone) 24ainfections 56c-d, 57cinferior oblique muscle

23dinferior rectus muscle

23dinferior vena cava 33a-c,

33d, 34a-b, 34c-dinflammation 56binsulin 53aintegumentary system 6-7c

see also hair; nails; skinintervertebral disc 17dintestines 6-7c, 38, 39, 41,

42, 53involuntary muscles 12b-diodine 40airis 23a-ciron 40a, 40b, 41cislets 53a

Jjaundice 43a

jaw 17c, 28-9joints 6-7a, 16-17

Kkeratin 9a, 11a-c, 11dkidneys 6-7a, 35a-c,36b-d, 37a-b, 40a, 44-

5, 52c-d, 53cknee 14a, 15d,17a-c, 17dknuckles 17d

Llacrimal gland 23clarge intestine (colon)

38b-c, 39larynx (voice-box) 19d,

31dlateral rectus muscle 23dleft ventricle 33a-clegs 15d, 35a-clens 23a-cleucocytes (white blood

cells) 37, 53b, 54a,54b, 55

ligaments 16b, 17a-climbic system 26alipase 38b-dlipids 40b-dlips 26a-d, 27dliver 6-7c, 35a-c, 39a-c,

39d, 42-3long sight (hypermetropia)

23clumbar vertebrae 15dlungs 6-7a, 19d, 30-1,

56alunula 10b-dlymph see lymphatic systemlymphatic system 6-7b,

54-5lymphocytes 55a-c

Mmacrophages 55a-cmagnesium 15a-c, 40amalaria 57bmale sex organs 48amalleus (hammer) bone

24amalnutrition 56c-dmandible (lower jaw bone)

17c, 28a-cmarathon runners 51dmasseter muscle 13d,

28a-cmaxilla (upper jaw bone)

28a-c, 28dmedial rectus muscle 23dmedicines 56-7medulla, kidney 44a, 53cmeiosis 49a-cmemory cells 55cmenarche 51a-cmeninges 21a-bmenisci 17a-cmenstrual cycle 48a-d,

51a-cmetabolic conditions 56c-dmicrofungi 57amicrohairs 26a-d, 27a-cmicronerves 8amicrosensors 8c-d, 9a

microbes 6-7c, 39b-c, 57cmicrovilli 39dminerals 6-7a, 37d, 40,

41c, 53a-cmitosis 49a-cmitral valve 33a-c, 33dmolars 29cmotor nerves 12b-dmotor skills 20b-cmouth 6-7c, 38a, 38b-c,

39a-cmovement 6-7a, 6-7c,

12-13mucus 27c, 38b-dmuscles 6-7a, 6-7c, 12-13,

34a, 36a, 40a, 40c-d, 41a

blood flow 20a, 37a-bcontrol 21a-csee also body parts;named muscles

musculoskeletal system 6-7a, 6-7c, 16b-d

myelin sheath 19a-bmyocardium see cardiac

musclemyopia (short sight) 23cmyosin 13a-c

Nnails 6-7c, 8b-d, 10-11nasal see nosenatural acquired immunity

55dnausea 56bnephrons 44a-dnervous system 6-7a, 6-7c,

15a-c, 18-19, 40a, 40c-dsee also body parts;named nerves

neuroglia 20b-cneurologist 57dneurons 20b-cneurotransmitters 19cnicotinic acid (Vitamin B3)

41dnose 6-7a, 15a-b, 19d, 26-

7, 31a-cnutrients 6-7b, 6-7c, 40-1

Oobstetrician 57dodorants 26b-doils 40c-d, 42dolfactory patch 26a-dophthalmologist 57doptic disc 22aoptic nerve 22aorbicularis oculi (eyelid

muscles) 13dorgans 6-7a

INDEX INDEX

6362

Hhaematologist 57dhaemoglobin 37a-chair 6-7c, 8b-d, 9b, 10-11,

25a-chammer (malleus) bone

24ahands 15dhard palate 28dHaversian systems (osteons)

16ahay fever 56bhead 35a-chearing 24-5heart 6-7b, 19d, 20a, 32-

3, 34a-b, 35a-c, 53a-cand adrenaline 53dblood flow 37a-band brain 21a-csee also cardio-

heart disease 40c-dheart specialist 57dheartbeat 40a, 40c-d, 56ahepatic artery 35a-c, 43b-chepatic portal vein 43b-chepatic vein 35a-c

hepatitis 43ahinge joint 17dhips (pelvis) 15d, 17c, 17dhormonal (endocrine)

system 6-7a, 6-7b, 6-7c,52a, 52b-d

hormones 6-7c, 37d, 42-3,48a-d, 56a see also hormonal(endocrine) system

human genome 46ahygiene 29dhyoid bone 14ahypermetropia (long sight)

23chypodermis 9chypothalamus 21a-c

Iidentical twins 47dileum 39diliac artery 35a-ciliac vein 35a-cimmmunosuppressives 56aimmune system 6-7b, 6-7c,

40a, 54-5immunization 55d, 57b-cincus (anvil bone) 24ainfections 56c-d, 57cinferior oblique muscle

23dinferior rectus muscle

23dinferior vena cava 33a-c,

33d, 34a-b, 34c-dinflammation 56binsulin 53aintegumentary system 6-7c

see also hair; nails; skinintervertebral disc 17dintestines 6-7c, 38, 39, 41,

42, 53involuntary muscles 12b-diodine 40airis 23a-ciron 40a, 40b, 41cislets 53a

Jjaundice 43a

jaw 17c, 28-9joints 6-7a, 16-17

Kkeratin 9a, 11a-c, 11dkidneys 6-7a, 35a-c,36b-d, 37a-b, 40a, 44-

5, 52c-d, 53cknee 14a, 15d,17a-c, 17dknuckles 17d

Llacrimal gland 23clarge intestine (colon)

38b-c, 39larynx (voice-box) 19d,

31dlateral rectus muscle 23dleft ventricle 33a-clegs 15d, 35a-clens 23a-cleucocytes (white blood

cells) 37, 53b, 54a,54b, 55

ligaments 16b, 17a-climbic system 26alipase 38b-dlipids 40b-dlips 26a-d, 27dliver 6-7c, 35a-c, 39a-c,

39d, 42-3long sight (hypermetropia)

23clumbar vertebrae 15dlungs 6-7a, 19d, 30-1,

56alunula 10b-dlymph see lymphatic systemlymphatic system 6-7b,

54-5lymphocytes 55a-c

Mmacrophages 55a-cmagnesium 15a-c, 40amalaria 57bmale sex organs 48amalleus (hammer) bone

24amalnutrition 56c-dmandible (lower jaw bone)

17c, 28a-cmarathon runners 51dmasseter muscle 13d,

28a-cmaxilla (upper jaw bone)

28a-c, 28dmedial rectus muscle 23dmedicines 56-7medulla, kidney 44a, 53cmeiosis 49a-cmemory cells 55cmenarche 51a-cmeninges 21a-bmenisci 17a-cmenstrual cycle 48a-d,

51a-cmetabolic conditions 56c-dmicrofungi 57amicrohairs 26a-d, 27a-cmicronerves 8amicrosensors 8c-d, 9a

microbes 6-7c, 39b-c, 57cmicrovilli 39dminerals 6-7a, 37d, 40,

41c, 53a-cmitosis 49a-cmitral valve 33a-c, 33dmolars 29cmotor nerves 12b-dmotor skills 20b-cmouth 6-7c, 38a, 38b-c,

39a-cmovement 6-7a, 6-7c,

12-13mucus 27c, 38b-dmuscles 6-7a, 6-7c, 12-13,

34a, 36a, 40a, 40c-d, 41a

blood flow 20a, 37a-bcontrol 21a-csee also body parts;named muscles

musculoskeletal system 6-7a, 6-7c, 16b-d

myelin sheath 19a-bmyocardium see cardiac

musclemyopia (short sight) 23cmyosin 13a-c

Nnails 6-7c, 8b-d, 10-11nasal see nosenatural acquired immunity

55dnausea 56bnephrons 44a-dnervous system 6-7a, 6-7c,

15a-c, 18-19, 40a, 40c-dsee also body parts;named nerves

neuroglia 20b-cneurologist 57dneurons 20b-cneurotransmitters 19cnicotinic acid (Vitamin B3)

41dnose 6-7a, 15a-b, 19d, 26-

7, 31a-cnutrients 6-7b, 6-7c, 40-1

Oobstetrician 57dodorants 26b-doils 40c-d, 42dolfactory patch 26a-dophthalmologist 57doptic disc 22aoptic nerve 22aorbicularis oculi (eyelid

muscles) 13dorgans 6-7a

see also named organsorthopaedic surgeon 57dossicles 25a-costeons (Haversian systems)

16aovaries 48b, 48c-d, 49d,

52a, 53a-coviducts (fallopian tubes)

48b, 48c-d, 50b-dovulation 48a-doxygen 6-7b, 30b-d, 31a-c,

34a-b, 37a-c, 37d

PPacinian sensors 9apaediatrician 57dpain 18bpalate 28dpalatine bone 28dpalatine tonsils 54c-dpancreas 39a-c, 39d,

42-3, 53a-cpapillae 27a-cparasites 57bparathyroid hormone (PTH)

52bparotid glands 29dpassive immunity 55dpatella (kneecap) 14apathologist 57dPCR (polymerase chain

reaction) 47a-cpelvis (hips) 15d, 17c, 17dpenis 45a-b, 49a-c, 49dpepsin 38b-dpericardium 33a-c, 33dperiod (menstrual bleeding)

48a-dperiosteum 16aperipheral nervous system

6-7a, 18aperistalsis 39apharyngeal tonsils

(adenoids) 54a, 54c-dphosphate 6-7c, 16b-dphylloquinone (Vitamin K)

40b, 41dphysiotherapist 57dpigments 47dpinna (auricle) 24apituitary gland 52c-dplaque 29a-cplasma 37d, 55a-cplatelets (thrombocytes) 37platysma 13aplicae 39dpoisons 42a-c, 56b, 56c-dpregnancy 50aprimary care physician 57procerus muscle 12a-dprogesterone 48a-d, 53a-c

prostate gland 49a-cproteins 13b-c, 38b-d,

40b-d, 41a, 43a, 45cprotist (protozoa) 55a-b,

57bprotozoa (protists) 55a-b,

57bpsychiatrist 57dpuberty 6-7b, 51a-cpubic hair 10b-d, 51a-cpulmonary arteries 33a-c,

34a-bpulmonary valve 33a-c,

33dpulmonary veins 33a-c,

34a-bpulse rate 32b-dpupil 23a-cpyridoxine (Vitamin B6)

41d

Rradiation 56c-dradiologist 57dreceptors (smell and taste)

26c-drecessive genes 47a-crectum 6-7c, 38b-c, 39a-cred blood cells

(erythrocytes) 37a-c,37d, 40a, 42a-c, 43a,56a

renal arteries 35a-c, 44b-drenal pelvis 44arenal tubule 44a-drenal veins 35a-c, 44b-dreproductive system 6-7b,

6-7c, 45a-b, 48-9respiratory system 6-7a,

30-1

rest and activity 20aretina 22a, 22b-d, 23a-criboflavin (Vitamin B2) 41dribs 14b-d, 15a-b, 15dright lymphatic duct 54brisorius muscle 12a-drods 22a, 22b-droughage (fiber) 39b-c,

40b-d, 41b-c

Ssacrum 15dsaddle joints 17dsaliva 27a-c, 29d,

39a-csalivary glands 39a-csartorius muscle 13dscalp 10b-dsciatic nerve 18c-dsclera 23a-cscratching 11dscrotum 49a-csebum 8asecretin 53a-csemicircular canals 25b-cseminiferous tubules 49dsenses see hearing; sensory

system; sight; smell;taste; touch

sensory system 6-7a, 6-7c,20b-c, 21a-c, 26a-d

septum 26b, 33a-c, 33dsex hormones 6-7c, 48a-dshin 15dshort sight (myopia) 23cshoulders 15d, 17dsight 22-3sigmoid colon 39dsinoatrial node 32c-d,

33a-c

skeletal muscles 12b-d,13dskeletal system 6-7a,

14-15, 16b-dskin 6-7c, 8-9, 19d, 37a-b,

40a, 41a, 56b, 57dskull 15dsleep 21csmall intestine 38b-c, 39a-

c, 39d, 42a-c, 42d,53a-c

smell 26a, 26c-d, 27a-c,40a

smile 12asmooth muscles 12b-dsneezing 30bsodium 40a, 41csoft palate 28dsound 6-7a, 24c-d, 25a,

25dspeech 6-7a, 27d, 31dsperm cells 6-7b, 48a-d,

49a-c, 49d, 50b-d

INDEX INDEX

64

spinal cord 6-7a, 18, 19a-b, 21a-c

spine (backbone) 15dspirochaetes 57aspleen 54a, 54c-dstapedius muscle 13dstapes (stirrup bone) 17c,

24a, 25b-csteroid hormones 53csteroids 56astirrup bone (stapes) 17c,

24a, 25b-cstomach 6-7c, 20a, 35a-c,

37a-b, 38, 39a-c, 53a-cstress 40a, 53cstriated muscles 12b-dstriped muscles 12b-dsubclavian veins 54bsublingual glands 29dsubmandibular glands 29dsugars 29a-c, 38b-d, 40c-dsulci 20b-csuntan 9dsuperior oblique muscle

23dsuperior rectus muscle 23dsuperior vena cava 33a-c,

33d, 34c-dsuture joint 17dswallowing muscles 19d,

28dsweat 6-7c, 8a-b, 8c-d, 9b,

9d, 45dsynapses 19csynovial fluid 17a-csynovial membrane 17a-c

Ttaste 26c-d, 27a-c, 40atear fluid 23cteeth 6-7c, 26a-d, 28-9,

39a-c, 40atemperature control 6-7c,

9d, 56btemporalis muscle 28a-ctendons 13b-c, 13d, 34aterminal bronchioles 31a-cterminal fibres 19dtestes 49a-c, 49d, 52a,

53a-ctestosterone 53a-cthalamus 21a-cthiamine (Vitamin B1) 41dthigh bones (femur) 15a-c,

15d, 17cthoracic duct 54bthoracic surgeon 57dthoracic vertebrae 15dthroat 6-7c, 31a-c, 38b-c,

39a-cthrombocytes (platelets) 37

thrombolytic 56athumb 17dthyamine 46athymopoietin 53bthymosin 53bthymus gland 53b, 54a,

55a-cthyroid cartilage (Adam’s

apple) 31dthyroid gland 52a, 52c-dthyroid-stimulating hormone

(TSH) 52c-dthyroxine (T4) 40a, 52atissue 6-7a

see also fatty tissue;muscle tissue

tocopherol (Vitamin E) 41dtoes 15dtongue 6-7c, 19d, 26-7,

39a-ctonsils 54a, 54c-dtouch 6-7c, 8a, 8b-d, 9d,

11d, 19d, 27a-ctoxins 42a-c, 56b, 56c-dtrace metallic elements

40b-dtrachea (windpipe) 6-7a,

30a, 31a-ctransplants 56atransverse colon 39dtri-iodothyronine (T3) 52atricuspid valve 33dturbinates 26b

Uurea 37d, 44a-dureter 6-7a, 44b-d,

45curethra 6-7a, 45a-b,

45c, 49a-c, 49durinary system 6-7a,

44-5urine 6-7a, 44, 45,

56aurologist 57duterus (womb) 48b,

48c-d

Vvaccination 55dvagina 48b, 48c-dvalves, heart 33dvas deferens (ductus

deferens) 49a-c, 49d

vascular supply 34bvasoconstrictor 56avasodilator 56aveins 34a-b, 34c-d,

35a-c, 35d, 36aventricles

brain 21a-b

heart 33dvenules 35a-c, 35dvertebrae 14c-d, 15dvertebral artery 20avestibular nerve 25a-cvilli 39dviruses 6-7c, 55a-b, 55c,

56b, 57b-cvisceral muscles 12b-dvitamins 9d, 40b-d, 41a-b,

41d, 42a-cvitreous humor 23a-cvocal cords 31dvoice, breaking 51a-cvoice-box (larynx) 19d,

31dvoluntary muscles 12b-d

Wwasher joints 17dwater 42a-cwhite blood cells

(leucocytes) 37,53b, 54a, 54b,55

windpipe (trachea) 6-7a,30a, 31a-c

wisdom teeth 29cwomb (uterus) 48b,

48c-dwound healing 40awrist 15d

Zzinc 40a

INDEX

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