bio 105: digestive system - napa valley college · the digestive system figure 15.1 (1 of 2) mouth...

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Bio 105: Digestive System

Lecture 18

Chapter 15

Copyright © 2009 Pearson Education Inc.1

Outline

• Function

• Layers of the gastrointestinal (GI) tract

•Major parts• Mouth, Pharynx, Esophagus, Stomach,

Small intestine, Large intestine, Pancreas, Liver, Gall Bladder

•Digestive Enzymes


The Digestive System

•Gastrointestinal tract• Long tube that extends from the mouth to

the anus• Includes accessory organs

•Divided into specialized compartments for food processing

•Nerves and hormones control digestive activities


Functions of the Digestive System

•Bring food into the body

•Digest it into nutrients• Nutrients then get absorbed by the body

• Eliminates wastes out of the body


Terminology

•Digestion• Process of breaking complex molecules

into simpler molecules which can be absorbed in the GI tract

•Absorption• Process of transporting molecules across

the wall of the GI tract into vessels to be transported to the liver


Digestion

•2 types• Mechanical Digestion

• Chewing of food, churning action of the stomach, segmentation of the small intestine

• Chemical Digestion• Action of enzymes and chemicals on foods


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Figure 15.1 (1 of 2)

Mouth

• Entrance to digestive system

• Teeth chew food

• Tongue positions and tastes food

Pharynx

• Passageway for food (and air)

• Plays a role in swallowing

Esophagus

• Muscular tube

• Moves food from pharynx to

stomach

Stomach

• J-shaped muscular sac

• Stores food

• Secretes gastric juice

(pepsin and HCl)

• Mixes food with gastric juice

• Protein digestion begins

Small intestine

• Long, muscular tube

• Mixes food with bile and with

intestinal and pancreatic

enzymes

• Digests most nutrients

• Absorbs most nutrients and

water

Colon

• Muscular tube

• Absorbs water and some

nutrients

• Stores waste materials

(feces)

Rectum

• Region of large intestine

• Passageway for feces

• Stretching of wall stimulates

the defecation reflex

Anus

• Opening at end of system

• Expels feces

Anal canal

• Regulates defecation

Cecum

• Blind pouch at junction of

small and large intestines

ORGANS

Large intestine



Figure 15.1 (2 of 2)

Salivary glands

• Three pairs of glands that

secrete saliva

• Saliva moistens food

• Enzyme (amylase) in saliva

begins starch digestion

Pancreas

• Gland located behind

stomach

• Secretes enzymes that

digest all major

nutrients

• Secretes buffers that

neutralize HCl from

stomach

• Releases secretions

into small intestine

Gallbladder

• Small sac

• Stores bile

• Releases bile into small

intestine

Liver

• Large organ in

abdominal cavity

• Secretes bile, which

emulsifies fats

• Plays role in

processing and storing

certain nutrients

ACCESSORY STRUCTURES


Review Question

•What type of epithelial tissue lines the GI tract?• Simple cuboidal• Simple squamous• Simple columnar• Stratified squamous


Wall of the Digestive Tract

•4 basic layers• Mucosa• Submucosa• Muscularis• Serosa



Figure 15.2

The mucosa is a mucousmembrane that lines theGI tract and secretesmucus that lubricates andprotects the GI tract.

The muscularis is madeup of two layers of smoothmuscle—one circular andone longitudinal.

The serosa is aconnective tissuecovering that secretesa fluid to lubricate theoutside of the GI tract.

The submucosa is a layerof connective tissue thatcontains blood vessels,lymph vessels, and nerves.

Lumen

Lymphatic

vessel

Nerve

Blood

vessels



•Mucosa• Mucus membrane layer lines the GI tract

• Lumen • Open area inside the GI tract• Lined by simple columnar epithelial cells

• Glandular epithelial cells• Secrete digestive enzymes

• Goblet cells• Secrete mucus


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• Submucosa• Layer of connective tissue with nerves,

blood supply, lymph vessels

• Protects us from disease• Nerves stimulate muscles• Transport of nutrients



•Muscularis• Layer of smooth muscles

• Has 2 layers of muscle• Circular layer

• Longitudinal layer

• Functions to mix and moves food



• Serosa• Layer covering the GI tract that secretes

serous fluid

• Fluid functions to reduce friction between moving layers of tissue


Components of the GI Tract

•Major GI tract (alimentary canal) components• Mouth• Esophagus• Stomach• Small Intestine• Large Intestine


•Aid the digestive organs

• Include• Salivary glands• Pancreas• Gallbladder• Liver

Accessory Organs


The Digestive System Has Specialized Compartments

Table 15.1


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Digestive Tract - Mouth

• Specialized for • Tasting• Speech• Moistening food• Mechanical digestion• Enzymatic digestion


Digestive Tract - Mouth• The mouth contains

• Salivary glands• Secrete salivary amylase that begins the process

of digesting starch

• Tongue• Mixes chewed food with saliva

• Teeth• Break food into smaller pieces

• Tonsils• Protect against infections

• Uvula• Working with the soft palate, closes off the

nasopharynx during swallowingCopyright © 2009 Pearson Education Inc.20


• Saliva• Moistens food• Dissolves the chemicals in food• Contains the enzyme salivary amylase• Produced by 3 major pairs of glands

• Parotid salivary glands

• Sublingual salivary glands

• Submandibular salivary glands


Salivary glands

Figure 15.5



• Tongue• Large skeletal muscle with taste buds• Important in speech• Helps form food into a bolus


Teeth

Figure 15.3b

Enamel

Crown

Root

Dentin

Gum (gingiva)

Pulp cavity

(contains blood

vessels and

nerves)

Root canal

Cementum

Bone

(b) The structure of the human tooth is suited for its function of

breaking food into smaller pieces.Copyright © 2009 Pearson Education Inc.24

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Digestive Tract - Pharynx

•Behind the uvula•Nasal and oral cavities join here•Common passageway for air, liquids and

food• Swallowing reflex begins here• Epiglottis

• Covers opening in the larynx that leads to the trachea when swallowing


Digestive Tract - Esophagus

•Passage that connects the pharynx to the stomach

•No digestive processes occur here

•Peristalsis • Series of muscular contractions that push

food through our digestive system• Occurs in esophagus


Esophagus

Figure 15.7


Digestive Tract - Esophagus

• Sphincters• Circular muscles that control the entrance

and exit of materials to and from the stomach

• Acid reflux• Heartburn• Occurs when partially digested food comes

back up into the esophagus• Produces a burning sensation• AKA “GERD”

• Gastro-Esophageal Reflux Disease


Digestive Tract - Stomach

•Breaks up food through muscular contractions

•3 layers of smooth muscle

• Food that leaves the stomach is only partially digested


Stomach

Figure 15.8a


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• Functions• Responsible for the storage of food• Turns food into a soupy mixture

• Chyme

• Adds digestive enzymes and acids that begin chemical digestion of proteins



• Storage of food• Stomach expands to accommodate

amounts of food• When empty can hold about 50 ml (1/4

cup)• When full can hold several liters of food• Very little nutrition is actually absorbed into

the blood stream • Exceptions – alcohol and some drugs (aspirin)


Review Questions

• The thick, soupy, acidic liquid that leaves the stomach is called what?



• Secretions

• Gastric glands secrete• Pepsin

• Digestive enzyme• Begins the digestion of proteins

• Hydrochloric Acid (HCl)• Strong acid• Kills bacteria• Aids in digestion of proteins• Beings to breakdown connective tissues• Activates pepsin

•Wall protected by a thick layer of mucus


Layers of the Stomach

Figure 15.8b

Surface epithelium

Mucosa

Submucosa

Muscularis

Serosa

Gastric pit

Mucus-secreting cell

Pepsinogen-

secreting cell

HCl-secreting cell

Blood vessels

(b) Gastric glands in the wall of the stomach

produce gastric juice, a mixture of

hydrochloric acid and pepsin.Copyright © 2009 Pearson Education Inc.35

Gastric Pits

Figure 15.8c


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Review Questions

• How many layers of smooth muscle are in the wall of the stomach?•What is the muscular tube that passes

foodstuffs from the pharynx to the stomach?•What is the primary function of the

stomach?• Breakdown fats• Store food, liquefy and begin digestion• Absorb major nutrients• Package feces

Copyright © 2009 Pearson Education Inc.37 Copyright © 2009 Pearson Education Inc.38

Digestive Tract – Small Intestine

•3 regions• Duodenum• Jejunum• Ileum



•Primary site of digestion• Mainly chemical but also mechanical

•Where most (80%) of the nutrients are absorbed into the body



• Thin long tube • 2.5 cm in diameter• About 6 meters long

• Secretions from the pancreas, liver and gall bladder enter the small intestine

• Smooth muscles surround the intestine to push food through



•Digestion of complex molecules• Carbohydrates• Proteins• Fats• Nucleic acids

•Aided by• Enzymes in the wall of the small intestine

and released from the pancreas• Bile from the gall bladder


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• Lining• Pleated (has circular folds)• Pleats have numerous finger-like

projections• Villi

• Increase surface area


Small Intestine

Figure 15.9a


Small Intestine - Villi

Figure 15.9b–c



•Villi• Villus (singular)• Greatly increase the absorption area of

the SI• Contain blood capillaries and lymphatic

vessels called lacteals• Blood capillaries – absorb nutrients including

glucose and amino acids

• Lacteals – absorb fatty acids



•Absorption • Complex molecules are broken down• Transported across the intestine wall

• Each villus contains a network of capillaries and a lacteal



•Microvilli• Each villus is covered with microvilli• Velvety appearance• Increases surface area• Called “Brushed border”


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Villi

Figure 15.9d–e



• Enzymes• Found in the walls of the cells in the brush

border• Carbohydrate enzymes that break down

di-, tri- and polysaccharides into monosaccharides• Maltase, Lactase, Sucrase

• Peptidases • Break peptides into amino acids


Digestive Tract – Large Intestine

•Most of the nutrients already absorbed

• Functions• Water, salts & Vitamins absorbed• Stores feces• Eliminates feces from the body


Large Intestine

Figure 15.14

Ascending colon

Transverse colon

Descending colon

External

anal sphincter

Rectum

Anal canal

Appendix

Cecum

Small intestine



•Components• Cecum

• Lies below the junction with the small intestine

• Appendix• Slender pouch extending from the cecum

• May play a role in fighting infections

• Can become inflammed



•Components, cont’d• Colon

• Largest portion

• Absorbs much of the remaining water, sodium and potassium ions

• Beneficial bacteria

• Undigested food residue leaves as feces

• Ascending, Transverse, Descending


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•Components, cont’d• Rectum

• Holds feces temporarily and opens into the anus

• Anus• Sphincter muscles controls defecation


Review Question

•Where are nutrients primarily absorbed?


Accessory Organs of the Digestive System

Figure 15.11

StomachGallbladder

Common

bile duct

Liver

Pancreas

(behind

stomach)

Small

intestine

Pancreatic

duct

The liver produces

bile, which is stored in

the gallbladder before

being released into

the small intestine.

The pancreas produces

several digestive

enzymes that act in the

small intestine Copyright © 2009 Pearson Education Inc.57

Accessory Organs - Pancreas

•Releases secretions into the small intestine to aid in digestion

•Also a gland that releases hormones



• Functions• Produces the hormones that are released

into the bloodstream to regulate glucose levels

• Secretes digestive enzymes• Secretes bicarbonate ions



• Secretes two hormones into the blood to regulate glucose• Insulin• Glucagon


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•4 types of enzymes• Amylase• Proteases• Lipase• Nucleases


Accessory Organs - Liver

•Hepatic portal veins• Blood from capillaries of the intestine,

carrying nutrients, goes to the liver through the portal veins

•2 blood supplies• Nutrient rich, oxygen poor blood• Nutrient poor, oxygen rich blood


Hepatic Portal System

Figure 15.12

Inferior

vena cava

Capillary

bed in

liver

Capillary

bed in

intestine

Liver

Hepatic

veins

Stomach

Small

intestine

Large

intestine

Step 4: Hepatic veins

deliver blood to the

circulatory system.

Step 2: Digested

food molecules then

travel through

hepatic portal veins

to the liver.

Step 1: Products of

digestion are

absorbed into the

capillaries within the

villi of the small

intestine.

Step 3: The liver

monitors blood

contents.



•Digestive Functions• Produces bile• Processes nutrients from the digestive

tract• Metabolizes drugs and toxins



•Other Liver functions• Produces plasma proteins• Breaks down old blood cells Produces

bilirubin• Breaks down amino acids urea• Stores iron and fat soluble vitamins• Stores glucose as glycogen• Regulates the quantity of cholesterol in

the blood


Accessory Organs - Gallbladder

• Stores excess bile

•Bile emulsifies fats


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Digestive Enzymes

•Break down macromolecules into smaller molecules


Review Questions

•What is the monomer unit of starch?•What is the monomer unit of proteins?•What is the monomer unit of DNA and

RNA?•Where is bile produced?•What digestive enzyme is responsible

for fat digestion?•Where is lipase secreted from?


Summary Table of EnzymesEnzyme Produced By Function

AmylaseSalivary Glands

PancreasBreaks down starch to maltose

CHO enzymes Small IntestineBreaks down di-, tri- and

polysaccharides into monosaccharides

Pepsin Stomach Breaks proteins into smaller pieces

PeptidasesSmall Intestine

PancreasBreaks proteins and polypeptides into

amino acids

Nucleases Pancreas Breaks nucleic acids into nucleotides

Lipase PancreasDigests fat molecules into monoglyceride fatty acids

Bile Liver Emulsification of fatsCopyright © 2009 Pearson Education Inc.69

Important Concepts

•What is the purpose of the digestive system?

•What are the layers of the GI tract?• Be able to describe the layers• What are the functions of the layers?

•What are the parts of the mouth and their functions?


Important Concepts

•What are the major parts of the digestive system and their functions?• Be able to describe the parts of the digestive

system• Mouth, pharynx, esophagus, stomach, small

intestine, large intestine, pancreas, liver, gallbladder

•What are the 3 regions of the small intestine? What is their order? (How does food pass through them)


Important Concepts

• How is food absorbed in the small intestine?

• How are fats absorbed vs other nutrients?

•What is the structure of villi?

•What is the role of blood capillaries and lacteals?

•What is the role of bile and lipase in fat digestion?


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Important Concepts

•What type of muscle is found in the wall of the GI tract?

•How many layers are in the stomach? How many layers are in the rest of the GI tract?

•What is the function of these muscles?


Important Concepts

•What are the components of the large intestine and their functions?•What is the function of bile?

•What do pancreatic secretions contain? What are their functions?

•What are the digestive enzymes and chemical secretions (bile and acid)?• What are their specific functions?• Where are they secreted from?


Important Concepts

•What is the function of the acid secreted in the stomach?

•What is the function of goblet cells?


Definitions

• Gastrointestinal (GI) tract• Digestion• Absorption• Mechanical digestion• Chemical digestion• Lumen• Peristalsis• Chyme• Bolus• Sphincters

• Villi• Microvilli• Brush border• Lacteals• Bilirubin• Goblet cells• Emulsifies/Emulsification• Feces


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