The digestive system.

  1. The digestive system is made up of the alimentary canal and some other parts that are important during digestion.
  2. The parts that together with the alimentary canal form the digestive system are:
    1. Pancreas
    2. Liver
    3. Gall bladder.

 The digestive system.


Functions of different parts.

Different parts of the digestive system include; mouth, oesophagus (gullet) stomach, duodenum, ileum, colon, rectum and anus.

 The teeth:

Break food in smaller particles hence increasing the surface area for the action of enzymes.

The tongue:

  1. Tastes food.
  2. Rolls the food into a bolus.
  3. Pushes food into the gullet.

The epiglottis:

It prevents foreign particles from entering the trachea.

   The soft palate:

Prevents food from entering the nasal cavity.

The stomach:

  1. Temporary store for food.
  2. Produces gastric juice.
  3. Produces hydrochloric acid.
  4. Absorbs alcohol.

 The liver:

Produces bile.

The pyloric sphincter:

It is a strong muscle which holds food in the stomach and lets it into the duodenum at intervals.

 The gull bladder:

Stores bile.

The pancreas:

Produces pancreatic juice.

 The ileum:

  1. Produces intestinal juice.
  2. Final digestion of food takes place here.
  3. Absorption of digested food takes place here.

The Colon:

Absorbs water from the undigested food.

 The rectum:

This is a temporary store for undigested food until it released through the anus.


Passes out the undigested food as faeces.


  1. In the mouth both chemical and mechanical digestion take place.
  2. Food is chewed by the teeth and mixed with saliva.
  3. Chewing increases the surface area for the action of enzymes.
  4. Chewed food is rolled into bolus by the tongue.
  5. Saliva is produced by the salivary glands in the mouth.
  6. The saliva contains an enzyme called salivary amylase/ptyaline.
  7. Salivary amylase digests cooked starch.

 Functions of saliva.

  1. Softens food.
  2. Lubricate food for easy swallowing.
  3. Contains an enzyme called salivary amylase (ptyalin) that acts upon cooked starch

Factors that stimulate the production of saliva.

  1. Smell of the food.
  2. Sight of food.
  3. Taste of food.
  4. Expectation for the food.


  1. It is a muscular tube that runs from the mouth leading to the stomach.
  2. Food rolls down through it by wave – like contractions called

  Illustration of peristalsis.

          Digestion in the stomach:

  1. The movement of muscles of the stomach churn the food into a semi-solid substance called chyme.
  2. The stomach walls secret (produce) gastric juice.
  3. Gastric juice contains hydrochloric acid and two enzymes namely;
  4. pepsin.
  5. rennin.
  6. Pepsin digests proteins changing it to
  7. Rennin clots the milk in babies in order to separate fats and protein.

Functions of hydrochloric acid.

  1. Stops the action of the salivary amylase.
  2. Provides suitable acidic conditions in which pepsin works best.
  3. Kills the bacteria which may have been taken in with the food.

 Digestion in the duodenum.

The region of the duodenum contains the liver, gall bladder and pancrease.

The Liver

  1. The liver produces bile and stores it in the gall bladder.
  2. Bile is green in colour.
  3. Bile has no enzyme but only bile salts.
  4. The bile salts emulsify (break) down fats.
  5. Bile juice is poured in to the duodenum by the gall bladder through the bile duct.


  1. The pancrease produces a juice called pancreatic juice.
  2. Pancreatic juice is also poured in the duodenum through the pancreatic duct.
  3. Pancreatic juice contains enzymes like;
  4. i) Pancreatic amylase
  5. ii) Lipase

iii) Trypsin.

 Pancreatic amylase.

  1. Pancreatic amylase digests any starch that skipped from the mouth undigested.
  2. It converts starch to maltose.


Breaks down fats to fatty acids and glycerol.


Breaks down proteins to peptides and peptides to amino acids.

Digestion in the ileum.

  1. Digestion of food is completed here.
  2. The ileum secretes an intestinal juice called succus intericus.
  3. The above juice has four enzymes.
    1. maltase
    2. Lactase
    3. Sucrace
    4. Erepsin/peptidase.


Breaks down maltose to glucose.


 Acts upon lactose to glucose and galactose.


Breaks down sucrose to glucose and fructose.


Breaks down peptides to amino acids.

 Absorption in the ileum.

  1. Absorption of digested food takes place in the ileum.
  2. This takes place with the help of the finger-like structures called villi.

 Adaptation of the ileum to absorption of digested food.

  1. The ileum is long enough to provide a larger surface area for absorption.
  2. It has villi, which also help to increase the surface area for absorption of digested food.
  3. Each villus has a thin membrane for digested food to pass through them easily.
  4. Each villus has dense network of capillaries that facilitate absorption.

Adaptation of the villi to absorption of digested food.

  1. Each villus is one cell thick and this makes it possible for digested food to pass through them easily.          
  1. Each villus has dense network of capillaries that enable easy absorption of the digested
  2. Food

 Processes that take place in the ileum.

  1. Digestion of food.
  2. Absorption of digested food.

The colon and the rectum

  1. Digestion does not take place in the colon and the rectum because they do not secrete
  2. The major process that takes place in the colon is absorption of water.
  3. It passes undigested material down to the rectum where it is temporarily stored till it is ready to be passed out through the anus.
  4. The passing out of the undigested food from the alimentary canal is called egestion.

 Summery of the food class and its end product.




Digestive juice


Food changes



Salivary gland


Salivary amylase

Salivary amylase




Stomach walls

Gastric juice


Protein to peptides


Clots milk.






No enzyme

Emulsify fats.


Pancreatic juice.

Pancreatic amylase.

Starch to maltose



fats to fatty acids and




Intestine walls

Succus intericus


Maltose to glucose



Lactose to glucose



Sucrose to glucose



peptides to amino acids


How digested food is used in the body.

  1. Glucose:
  2. used to generate energy through respiration.
  3. used to generate body heat through respiration.
  1. Amino acids:
  2. are re-assembled to form proteins used to make new body cells for one to grow.
  3. are re-assembled to form proteins used to repair worn out tissues.
  1. Fats:
  2. used to generate energy and heat.
  3. acts as a body insulator.

 Note: Twice as much energy is obtained from fats than glucose.

  1. Vitamins and mineral salts:

Keep us healthy so, they act as protective foods.

          Some important mineral salts needed by our bodies.


  1. Found in meat, liver, iron tablets, beans, peas egg yolk and green vegetables.
  2. It’s necessary for the manufacture of red blood cells.
  3. Shortage of iron in the diet leads to anaemia.

Other factors that lead to anaemia.

  1. Severe bleeding.
  2. Severe hookworm infection.
  3. Destruction of the red blood cells by plasmodia parasite that cause malaria.
  4. Failure of the red bone marrow to manufacture red blood cells.

How the problem of anaemia is solved in patients.

  1. Eating foods rich in iron.
  2. Through blood transfusion.
  1. Iodine:
  2. Found in iodised salt and seafood like crabs, sea fish etc.
  3. It’s necessary for proper functioning of the thyroid gland.
  4. Its deficiency leads to goitre.
  • Calcium and phosphorus.
  1. Present in the milk and hard water.
  2. They are necessary for the formation of strong bones.
  3. Their deficiency leads to the formation of weak bones.

Some imortant vitamins for our bodies.

 Vitamin A:

  1. Found in milk, green vegetables, liver, pepper, carrots, pawpaw, tomatoes palm oil etc.
  2. It’s necessary for good eyesight.
  3. Its deficiency leads to poor night vision.
  1. Vitamin B1:
  2. Contained in yeast, ground nuts and unpolished rice.
  3. Necessary for the prevention of beriberi.
  4. Its deficiency leads to beriberi.


  1. Other vitamin B2:
  2. Found in yeast, groundnuts, yams, milk, meat and egg yolk.
  3. Their deficiency leads to pellagra.
  1. Vitamin C:
  2. Found in oranges, lemon, row mangoes, guava paw paws and green vegetables.
  3. Necessary for the prevention of scurvy.
  4. Its deficiency leads to scurvy.
  1. Vitamin D:
  2. Contained in milk, egg yolk, fish liver oil etc.
  3. Necessary for the prevention of rickets.
  4. Its deficiency leads to rickets.
  1. Vitamin E:
  2. Present in green vegetables, butter, eggs, grains and nuts.
  3. Necessary for reproduction.
  4. Its deficiency leads to the poor formation of reproductive cells.
  1. Vitamin K:
  2. Present in green vegetable especially cabbage and spinach.
  3. Essential for blood clotting.
  4. Its deficiency leads to poor blood clotting.


 Ulcers in the stomach and duodenum

  1. These are wounds in the stomach or duodenum.
  2. They are caused by excess hydrochloric acid which affects the walls.
  3. Production of excess acid may be stimulated by emotional upsets tobacco smocking and not eating food at regular intervals.


  1. This the condition where the appendix gets swollen due to infection or when it is filled with stones.
  2. The best remedy is to be removed surgically.



  1. This is caused by a bacteria. It makes the victim vomit very frequently and also have severe diarrhoea
  2. It usually causes dehydration that may result into death.


  1. This can be caused by a bacteria or amoeba.
  2. It spreads through contaminated food or water.

c)    It usually causes diarrhoea with blood which may cause dehydration that may result into death


This is the passing out of waterly stool. It may be a sign of a disease or a disease.

Worm infection

Disorders of the digestive system:

These are conditions in the digestive system that makes it to fail to function normally.


This is a condition where one passes out faeces with difficulty or fails to pass out these faeces.

  1. It is prevented by including roughage in the diet.
  2. Taking enough water after meals.

 Sources of roughage.

  1. Pineapple
  2. Mangoes
  3. Green vegetables

Intestinal obstruction:

Solved through surgical operation.



It is a condition where food fails to get digested properly.

 Causes of indigestion.

  1. Swallowing food without chewing.
  2. Over eating where the stomach is full and fails to turn the food.
  3. Food poisoning and food infection can also cause indigestion.
  4. Bad teeth which do not chew food well.
  1. Emotional upsets can also cause indigestion.

When indigestion occurs, a person;

  1. Feels discomfort in the stomach.
  2. Feels heart burn.
  3. Belches smelly gas through the mouth.
  4. Passes out gas through the anus frequently.

 Causes of dis orders are;

  1. Not eating meals at regular times.
  2. Failure to chew food thoroughly
  3. Not doing exercises
  4. Not taking enough water after meals
  5. Not emptying bowels at regular intervals .
  6. Not eating food with roughage