Process of Digestion

The processes of digestion include six activities: ingestion, propulsion, mechanical or physical digestion, chemical digestion, absorption, and defecation. Digestion of food begins in the mouth.

Mouth

The mouth In the mouth, the food is mixed and softened with saliva. 

It is masticated and crushed into smaller particles by the teeth. Mastication exposes the food to the action of the enzymes. 

Saliva performs the following functions: 

1. It contains mucin which lubricates the food and makes swallowing easier. 

2. It provides an alkaline medium necessary for the action of the enzyme – ptyalin. 

Stomach

The stomach contains a juice called gastric juice which is acidic due to the presence of hydrochloric acid (HCL). 

The gastric juice also contains two enzymes – rennin and pepsin which act on the protein content in the food. 

The hydrochloric acid performs three major functions, which are: 

1. It stops the action of ptyalin from the mouth 

2. It provides the acidic medium necessary for the action of rennin and pepsin in the stomach 

3. It destroys any bacteria that might have accompanied the food from the mouth. 

Rennin acts on soluble milk protein caseinogens and converts it to casein (curdled milk protein) which is insoluble. 

Pepsin acts on other proteins and converts them into smaller peptides and peptones. Protein is the only nutrient acted upon in the stomach. 

The Duodenum 

From the stomach, the products of digestion are passed into the duodenum. 

The pancreatic juice from the pancreas is secreted and bile from the liver is emptied into the duodenum. 

The bile only emulsifies the fats and oils present in the chyme. The pancreatic juice contains these three enzymes: 

1. Amylase – converts starch to maltose 

2. Trypsin – converts protein to peptides and peptones 

3. Lipase – converts fats to fatty acids and glycerol. 

The Small Intestine 

In the small intestine, the intestinal juice contains these enzymes: 

1. Maltase – converts maltose to glucose 

2. Lactase – converts lactose to glucose and galactose 

3. Sucrose – converts sucrose to glucose and fructose 

4. Peptidase - converts peptides and peptones to amino acids 

5. Lipase – converts fats to fatty acids and glycerol.

The end products are now absorbed into the body’s circulatory system for use. The simple sugars and amino acids enter the bloodstream directly while fatty acids enter through lymphatic system. Absorption of nutrients occurs in the small intestine through its lining called villi.