The digestive system

What is digestion? 

- Digestion is the process of breaking down food into smaller particles that can be absorbed easily and used by our bodies. Digestion begins in the mouth. 


The following are the reasons why our bodies need food:

  • We need to take in carbohydrates and fats to provide energy. Carbohydrates and fats are needed to provide heat to the body.

  • We need to take in proteins that will be used to build new flesh, new bones, and new muscles. We also need proteins to help in body repair and growth.
  • We need to take in vitamins and mineral salts to protect our bodies from diseases.

We need the digestive system to help in: 

  • Breaking down the food into smaller  sizes that make them easy to absorb.
  • Absorbing the food into our bodies for use in building the body, body repair and growth.
  • To get rid of indigestible material or useless material in the food we eat and any waste products that may be harmful to the body.

Parts of the digestive system

The digestive system comprises of the following parts:

  • Mouth 
  • Stomach 
  • Liver
  • Large intestine
  • Anus
  • Oesophagus
  • Small intestine
  • Pancreas
  • Rectum


  • The mouth has teeth, the jaw, the tongue, and saliva.
  • The jaw holds the teeth.
  • The teeth cut down the pieces of food into smaller pieces.

  • Saliva has chemicals that help in further breaking down the food.
  • Saliva lubricates the food making it easier to swallow.
  • It helps in digesting starch which is found in foods that contain carbohydrates for example maize and cassava.
  • The tongue rolls up the chewed foods into small balls, that can be swallowed.
  • The tongue helps during swallowing by pushing the food to the back of the mouth.

Sets of teeth

A person has two sets of teeth. The first set is the milk teeth also called the deciduous teethThis set consists of incisors, canines and premolars only. The total number of milk teeth is 20.

 The second set is composed of 32 teeth. This set is called the permanent teeth and it replaces the milk teeth.

The permanent set of teeth consists of incisors,canines, premolars and molars.  

Types of teeth

There are four different types of teeth: 

  • Incisors for nipping, cutting and biting. 
  • Canines for biting, cutting and tearing.

[resource: 2061, align: left]

  • Premolars for crushing, chewing and grinding.
  • Molars for crushing, chewing and grinding.

Teeth should be cleaned after every meal to prevent tooth decay.  Tooth decay is caused by food remains that remain in the mouth, in between the teeth and gum after feeding.

The part of teeth called pulp cavity carries blood vessels to provide nutrients and oxygen to the teeth. The pulp cavity also carries nerves.

This video shows how to brush teeth



Teeth related problems 

  1. Bad breath. 
  2. Bleeding gums.
  3. Cavities or holes in the teeth/ tooth decay.

Taking care of your teeth

Avoid eating sugary foods such as sweets and biscuits or drinking sugary juices.

Clean  teeth and mouth using a toothbrush and toothpaste or salt after every meal and then rinse the mouth with warm water. 


A chewed stick from non poisonous plants may be used as a tooth brush.Chew one end of the stick until it becomes soft. It can then be used with some salt or toothpaste.

 African toothbrush

Requirements for strong teeth 

Teeth are made of a very hard substance called dentine, which in turn is covered by even a harder substance called enamel.

The inner structure of  a tooth

To ensure the teeth remain hard and strong, one must:

  • Drink and eat calcium-rich foods.  Calcium makes teeth hard and strong. Such foods include milk and eggs.

  • Eat hard foods to clean the teeth and to exercise the teeth and jaws. Example of hard foods include carrots, sugar cane, pears, and coconut

Carrots and coconuts

  • Eating sugar-free foods and avoid sweets and cakes.
  • Do not misuse teeth through opening of soda bottles with the teeth or cracking hard things with the teeth.
  • Brush teeth frequently using fluoride toothpaste, which makes the teeth stronger.

 Fluoride toothpaste 

  • Proper care of the gum too by avoiding using dental floss 

 dental floss

  • Visit a dentist often, preferably after every six months for checking.


The stomach is like an elastic bag that keeps food temporarily. The stomach mixes the food continuously therefore breaking it up and then release some small amount at a time into the intestines.

Functions of the stomach

  • A temporary store for food.
  • Mixes the food that is eaten.
  • Release chemicals to break down the food into much smaller particles that can be digested easily.
  • Release acid that kills bacteria in the food.
  • Absorbs simple food, for example, glucose and water into the blood.


The intestine is divided into the small intestine and the large intestine.

The small intestine

The small intestine is a long narrow tube between the stomach and the large intestine where: 

  • Digestion of food takes place.
  • Water and nutrients are absorbed into the blood.
  • Undigested materials are pushed ahead into the large intestines.

The large intestine

Functions of the large intestine include:

  • To absorb most of the water still remaining.
  • Holding undigested material that forms the faeces which are pushed out.

Other organs involved in digestion


Produces chemicals (pancreatic juice) which continue the digestion of protein (found in foods like meat) and starch (found in maize).  



Produces the bile used to start the digestion of fats and oils.


It holds the indegestive material (waste matter and releases it to the anus).


Passes out the indigestible materials out of the body.


KCPE Topical Questions 

Standard 5

Digestive system 

1. Kamau chewed a piece of meat for some time and then swallowed it. At which part of his digestive system did the digestion of the meat start? 
A. Mouth   B. Stomach   C. Small intestines   D. Large intestines 


Study the diagram below and answer questions 2 and 3.

2. The parts labeled F, G and H are 




A.    Pancreas


Gall bladder   

B.    Gall bladder  



C.    Gall bladder



D.    Pancreas

Gall bladder



3. For which of the following food types does digestion start at E?

A. Carbohydrates  B. Proteins C. Vitamins D. Fats


4. Which of the following is a function of the pancreas? It 

A. Absorbs digested food.       B. Produces digestive juice.

C. Absorbs water                     D. Stores digested food


5. In which of the following parts of the digestive system does absorption of food take place?

A. Duodenum     B. Small intestines
C. Stomach         D. Large intestine


6. Which of the following body structures in the table below is NOT CORRECTLY matched to its function?



A.    Villi

Absorb digested food

B.    Large intestine    

Stores digested food

C.    Pancreas

Produces digestive juice

D.    Mouth

Food is broken down into small particles


Health Education 

Standard 4

Care of the teeth

Which one of the following DOES NOT help to prevent tooth decay?

A. Regular checking of teeth by a dentist
B. Eating sweets and sugary foods
C. Brushing teeth after every meal
D. Drinking plenty of milk regularly

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