3.3 human digestive system (note)

CHAPTER 3 :
NUTRITION

3.3 HUMAN DIGESTIVE SYSTEM

HUMAN DIGESTIVE SYSTEM

Digestion

1. Digestion is the process of breaking down complex
food to simple molecules for absorption the blood
circulatory system.

2. Digestion take place in two stages:

a. physical digestion – big pieces of food are
broken down into smaller pieces by teeth

b. chemical digestion – enzymes break up
complex food molecules into smaller molecules





3. Enzymes are proteins that speed up the process of digestion.
Enzymes break up complex food molecules to smaller and
simpler molecules.

4. Characteristic of enzymes
a. enzymes are small quantities only

a. enzymes are not destroyed at the end of digestion

b. specific enzymes act only in specific acidic or alkaline conditions

c. specific enzymes act only on specific foods

d. enzymes function best at normal body temperature (370 C) Enzymes
are destroyed at high temperature.

1. The digestive system consists of all the organ in the body
that help in the digestion of food.

2. The alimentary canal is made up of the mouth, oesophagus,
stomach, small intestine, big intestine and anus (starts from
the mouth and ends at the anus).

3. Summary of the digestive system

mouth oesophagus stomach small
intestine big intestine anus

• MOUTH

1. Food is chewed and broken up into small pieces by
the teeth.

2. aTnhde csaolnivtaairnysgslaalnivdasreycaremtyelsassealeivnazythmaetsi.s alkaline
3. Salivary amylase digests starch into maltose

(sugar)
4. Osmuraltlobnaglul e(broollulss)thwehpicahrtaiarellythdeingesswteadllofowoeddiinnttoo

the oesophagus

starch Amylase maltose

• OESOPHAGUS

1. Food is pushed through the oesophagus into the stomach by
the alternating contraction and relaxation of the
oesophagus.

2. This process of alternating muscular contraction and
relaxation is known as peristalsis.

3. No digestion takes place in the oesophagus.

• stomach

1. The stomach is a muscular bag with walls that secrete
hydrochloric acid, water and protease.

2. The function of hydrochloric acid include
a. providing an acidic medium for enzymic action.
b. killing bacteria found in food
c. neutralising the alkaline property of saliva

3. Protease helps to digest proteins into amino acids.

4. Pepsin digest protien to peptones / polypeptides

Protien pepsin peptones/ polypeptides

5. Rennin coagulates milk in the stomach to help in the
enzymic enzymes.

rennin

Liquid milk protiens solid milk protiens

• LIVER AND PANCREAS

1. The liver and pancreas deliver their enzymes or secretions
to a small intestine through small tubes.

2. The liver produce bile, a substance that breaks up large fat
droplets into smaller particles.

3. Bile flow from liver to a gall bladder, the organ that stores
bile.

Small intestine

1. The duodenum is the first part of the small intestine.
2. The duodenum received bile and pancreatic juice.
3. The function of bile are:

a. emulsification of fat
b. preparation of an alkaline medium for enzymic action
4. Pancreatic juice contains three types of enzymes:
a. maltase
b. protease
c. lipase

5. The maltase digests maltose into glucose

maltose maltase glucose

6. The protease digests peptones into amino acids

protease amino acids

peptones

7. The lipase digests fat into fatty acid and glycerol

lipase fatty acids + glycerol

fat

8. Digestion is completed in small intestine.
9. The digest food is then ready to be absorbed through

the thin walls of the small intestine into the bloodstream.
10. Food digestion is completed in the small intestine.
11.The end products of digestion are

a.Carbohydrate - glucose
a. Protien- amino acids
b.Fats - fatty acids and glycerol .

LARGE INTESTINE

1. Water is reabsorbed in the big intestine
2. Undigested food is expelled from the

body through the anus as faeces.