C H A P T E R 1 1

MAMMALIAN NUTRITION

REQUIREMENT FOR FOOD• A balanced diet must contain:• - Fats• - Proteins• - Carbohydrates• - Vitamins & Minerals• All foods contain the

elements Carbon (C), Hydrogen (H) & Oxygen (O).

• Protein also contains Nitrogen (N)

• Age, gender, body size, occupation - all affect food requirements

FATS

• Energy-rich (twice as much as energy as carbohydrates)

• Made up of 2 components

• - glycerol & 3 fatty acid molecules

• Fat is insoluble• Stored around the

organs to provide a layer of padding & insulation

CARBOHYDRATES• Glucose (C6H12O6) is the most

common simple sugar• Glucose molecules (soluble) can join

to form larger carbohydrates (insoluble)

• In animals • – glucose stored as glycogen (in

liver)• In plants • – stored as starch • - converted to cellulose (in cell

walls)• - indigestible (forms roughage in

diet)

PROTEIN• Made up of amino acids• Protein is used for tissue

growth & repair• Human body cannot store

excess protein • - (minimum daily intake 80g)• Excess protein is used for

energy• Structural proteins are only

ever used for energy in an emergency (starvation)

VITAMINS• 2 types : • Fat soluble (e.g. A & D)• Water soluble (e.g. B &

C)• Work as coenzymes to

promote chemical reactions• Are constantly re-used,

so only required in small quantities

MINERALS

• Chemical components of food required for many functions in the body

• Calcium (dairy foods): • - hardening bones & teeth• Iron (meat & eggs): • - structural component of

haemoglobin• Sodium/Potassium (in most

foods):• - for muscle contraction

and nerve impulses

FOOD TESTS• Starch• - will turn iodine solution

blue/black• Protein• - will turn Biuret reagent lilac• Simple Sugar• - will turn heated Benedicts

solution orange• Fat• - produces a translucent stain

on white paper• - OR red layer with Sudan III

NEED FOR DIGESTION• Food is needed for cells:• Give fuel for energy• Provide building materials for • - growth• - repair• - fighting infection (antibody

production)• Digestion breaks down large

insoluble molecules • - into small soluble molecules• These molecules can then be

absorbed into the bloodstream

ALIMENTARY CANAL• A long tube running from

mouth to anus• Has several associated

organs connected to it • e.g. liver, pancreas,

salivary glands• These organs are

connected by tubes or ducts

Pharynx (throat)Oesophagus

MOUTH & SALIVARY GLANDS• In the mouth food is broken

down in 2 ways:• mechanically • - by chewing and grinding of

teeth• chemically • - by amylase, from the salivary

glands (starch into maltose)• saliva also contains mucus• - keeps the mouth & food

lubricated

OESOPHAGUS & PERISTALSIS• Oesophagus is a muscular

tube• - connects the mouth to

the stomach• It’s wall is lined with

circular muscle• Contraction & relaxation of

this muscle pushes food along• This is known as Peristalsis

STOMACH• A muscular sac, lined

with 2 types of muscle• - longtitudinal & circular

muscle• Muscles contract & relax• - helps churn & mix food

with digestive juices• 2 sphincters at either end • - hold the contents inside

GASTRIC GLANDS• Found in the inner lining of the

stomach• - Mucus-secreting cells • mucus sticks to the stomach

lining • - protects it from acid and

digestive enzymes• - Acid-secreting and enzyme-

secreting glands • Acid lowers pH• - converts inactive pepsinogen

into pepsin• Pepsin can then converts protein

into peptides (amino acids)

ASSOCIATED ORGANS• Liver:• - produces bile • - processes products of

digestion• Gall Bladder:• - stores bile• - passes it into small

intestine via bile duct• - bile helps emulsify fat• Pancreas:• - produces amylase, trypsin,

& lipase

SMALL INTESTINE• Where the majority of

digestion (& all absorption) takes place• Food moved along by

peristalsis • Food broken down by

digestive enzymes• - e.g. amylase, lipase, trypsin• Digestion products absorbed

into the bloodstream

SMALL INTESTINE - STRUCTURE• Very long• Folded inner lining • -covered in finger-like

villi • The epithelial cells lining

the villi are folded into microvilli

• Provides a very large surface area for food absorption

• Lining is only 1 cell thick

SMALL INTESTINE - ABSORPTION• Has a very dense network

of blood vessels• Each villus has a blood

capillary and lacteal• Glucose & amino acids

pass into the capillary • Fat digestion products

pass into the lacteal • Vitamins & minerals also

pass across

FATE OF ABSORBED MATERIALS• Amino acids & glucose:• - passed to the liver through the hepatic portal vein• Glucose : • - converted into glycogen & stored• - released into circulation as an energy source• Amino Acids :• Some used for growth & repair• Excess broken down into urea (deamination)• - removed by kidneys• Fat • - passed via the lymphatic system into the blood• - some used as an immediate energy source• - excess fatty acids & glycerol are converted into fat and stored in the

tissues• Vitamins & minerals • - carried by the blood to the cells that need them

LARGE INTESTINE• Undigested material,

bacteria & dead cells pass into the large intestine• Any excess water is

reabsorbed• The remaining faeces are

eliminated • - by passing to the rectum• Faeces are finally expelled

through the anus