FORM 2 CHAPTER 3 NUTRISION

2.3 HUMAN DIGESTIVE SYSTEM

Digestion (Pencernaan / 消化）
1. Digestion is the process of breaking down large,

complex food to small, simple molecules so that
they can be absorbed by the body cells.

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

a. Chemical digestion – enzymes break up

complex food molecules into simple molecules



2) Break up complex food molecules
to simpler molecules.

Comprises (terdiri daripada) ：

1. Digestive tract / Alimentary canal : A tube where food
passes that begins in the mouth and ends at the anus.

2. Organs :
(a) Liver (hati/肝）– Produce bile (hempedu / 胆汁）
(b) Gall bladder (Pundi hemperdu/胆囊） – Store bile
(c) Pancreas(Pankreas/胰腺） - produce pancreatic juice

Organs Digestive tract
mouth

oesophagus
stomach
duodenum

Small intestine
Large intestine

rectum
anus

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).

1) MOUTH
1. Food is chewed and broken up into small pieces by

the teeth. (Physical digestion)

2. Amylase in saliva break down starch into
maltose (chemical digestion)

2. Food in small ball shape (bolus).

* Digestion of carbohydrate starts:

starch Amylase maltose

2) OESOPHAGUS

1. Food is pushed through the oesophagus by the
contraction (mengecut 收缩） and relaxation
（mengendur/放松) of the oesophagus.

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

3. NO DIGESTION takes place in the oesophagus.

3) stomach

1. The stomach walls secretes (merembes/分泌)
hydrochloric acid (HCl) and Protease

2. The function of HCl :
a. providing an acidic medium for enzymic action.
b. killing bacteria found in food

* Digestion of protein starts:

Protease

Protein polypeptide

3. Food stays in stomach for about 4 hours. The
semi-liquid food is called chyme.

4) Small intestine (duodenum)
1. The duodenum is the first part of the small intestine.

2. The duodenum received bile and pancreatic juice.

• Liver produces bile.
• Gall bladder stores bile and secrete bile into

duodenum

The function of bile are:
a. Break down fat into small droplets.
b. Prepare alkaline medium for enzyme action

4) Small intestine (duodenum)
The pancreas secretes pancreatic juice.

• Pancreatic juice contains 3 types of enzymes:

Amylase

1) Starch maltose.

Protease dipeptides.
2) Polypeptides

Lipase

3) Fat fatty acid + glycerol (ended)

* Digestion of fat starts and ends in duodenum.



5 ) Small intestine (Continue)

• Digestion continues in small intestine.

Maltase

1) maltose glucose. (ended)

2) Dipeptides Protease amino acid (ended

5) Small intestine (Continue)

• Digestion is completed/ended in small intestine.

• The digest food (end product) is then ready to be absorbed
through the wall of small intestine into the bloodstream.

• The end products of digestion are:

FOOD CLASS END PRODUCT
(DIGESTED)
Carbohyrate Glucose
Protein Amino acid
Fat Fatty acid + Glycerol

3.4 Process of Absorption and Transportation
of Digested Food and Defecation

What happen to the end products of digestion? (glucose, amino acid, fatty
acid and glycerol)

Glucose, amino acid, water, Fatty acid, glycerol and vitamin A, D,
minerals, vitamin B & vitamin C will E, K will be absorbed into the lacteal,
be absorbed into the blood transfer to lymphatic system and then
circulatory system through the inner to blood circulatory system.

wall of small intestine.

Adaptations of small intestine to increase the
absorption of digested food :

1. The inner surface of the small intestine has many folds
called villi → to give a big surface area for absorption

2. The wall of villi/villus in very thin : only one cell thick →
digested food easily diffuse (meresap/渗透） through.

3. Network of blood capillaries around small intestine →
digested food easily diffuse from small intestine into the
bloodstream.



Why do vitamins and minerals not
require digestion?

Minerals, vitamins and water are already small enough to be absorbed
by the body, so they are not digested.

Enzymes cannot break down fibre, which is why the body cannot
absorb it.

Process of Transporting the Digested Product:

a) Digested food that is absorbed into the villus is then
transported to body cells through blood circulatory system.

b) Assimilation is the process of distributing the end product
of digestion for the use body cells.

➢ Glucose is to used to produce enegy.
➢ Amino acid is used to form component of cells.
➢ Fatty acid and glycerol combine to form fat → used as

heat insulator and protect internal organ

LARGE INTESTINE (NO DIGESTION)

1. Water is reabsorbed in the big intestine

2. Undigested food is expelled from the
body through the anus as faeces.

Reabsorption of Water and Defecation

Residue from the
small intestine

Reabsorption of water
+ minerals + vitamins

Solid waste called faeces

Stored in the last part of
the large intestine

Defecation through the anus

• Defecation is removal of faeces from the body through
the anus.

• Difficulty in defecation is called constipation.

• Prolonged and serious constipation can lead to …..
• Hemorrhoids (piles)
• Cancer of the large intestine

Why causes constipation?

Not eating enough roughage
Not drinking enough water

Therefore, constipation can be cured by:

• eating high fibre foods such as wholemeal cereals and

grains, fruits and vegetables.

• Drink more water.

The importance of a balanced diet

Good nutrition is an important part of leading a healthy lifestyle.
Combined with physical activity, your diet can help you to reach and
maintain a healthy weight, reduce your risk of chronic diseases (like
heart disease and cancer), and promote your overall health.

• Too much sugar → diabetes
• Too much salt → high blood pressure
• Too much fat → obesity, high blood cholesterol level, cancers
• Too much food → obesity
• Too little food → anorexia nervosa.
• Too little roughage → constipation.

Practise healthy eating habits by:
a) eating a balanced diet
b) drinking at least 7 glasses of water a day
c)consuming less fats, sugar and salt
d) eating plenty of fruit and vegetables
e) eating in moderation.