3.3	Human Digestive System

• Food digestion is a process of breaking down food that is complex into small molecules and soluble so that they can absorbed by the body cells

Digestion

Physical

The process of breaking down food into smaller particles with the help of teeth,tounge and saliva. Involves peristalsis

Happens in the mouth

Does not involve enzymes

 

Chemical

The process of breaking down food from complex molecules into simple molecules with the help of enzyme

Happens in the mouth,stomach,duodenum and intestine

Involves enzymes

 

The Structure of the Human Digestive System

1)Mouth

• Food is chewed by teeth.
• Salivary amylase in saliva breaks down starch into maltose.

 

2) Oesophagus 

• Food that enters oesophagus is called bolus.
• The process of peristalsis pushes the food into the stomach.

 

3)Stomach 

• Wall of stomach secrete protease and hydrochloric acid.
• Hydrochloric acid activates protease which breaks down protein into polypeptides. Semi-liquid food is called chyme.

 

4) Duodenum 

• Liver produces bile which emulsifies fat into small droplets and neutralises the acid in the chyme.
• Pancreas produces pancrestic juice which contain enzymes amylase,protease and lipase.
• Pancreatic amylase digests starch into maltose
• Protease digests polypeptides into dipeptides
• Lipase digests fat into fatty acids and glycerol

 

5) Small intestine

• Maltase digests maltose into glucose
• Protease digests dipeptides into amino acids

 

6) Large intestine

• Undigested food enters large intestine
• The process of water reabsorption happens 

 

7) Rectum

• Food that is undigested, known as faeces, enters the rectum and is stored here

 

8) Anus

• Faeces are excreted from the body through the anus