Digestive System
Digestive System
The complete process of nutrition is divided into five stages :
1. Ingestion
2. Digestion
3. Absorption
4. Assimilation
5. Defecation
1. Ingestion
Taking the food into the mouth is called Ingestion.
2. Digestion
Conversion of non absorbable food into absorbable form. The digestion of the food is started from the mouth.
» Saliva is secreted by salivary gland in mouth in which enzyme amylase is present. They convert starch into simple sugar and make it digestible.
» In human secretion of saliva is approximately 1.5 litre per day.
» The nature of saliva is acidic (pH 6.8).
» From the mouth food reach into stomach through food pipe.
» No digestion takes place in food pipe.
» The teeth used for grinding of food is molar.
Digestion in Stomach
» The foods lies approximately for four hours in stomach.
» After reaching the food in stomach gastric glands secretes the gastric juice. This is a light yellow acidic liquid.
» Hydrochloric add secreted from the Oxyntic cells of the stomach kills all the bacteria coming with food and accelerates the reaction of enzymes. Hydrochloric acid makes the food acidic by which amylase reaction of the saliva end.
» The enzymes in the gastric juice of stomach are - Pepsin and Renin.
» Pepsin breaks down the protein into peptones.
» Renin breaks down the Caseinogen into Casein found in milk.
Digestion in Duodenum
» As soon as the food reaches the duodenum bile juice from liver combines with it. Bile juice is an alkaline and it turns the acidic medium of food into alkaline.
» Here, pancreatic juice from pancreas combines with food. It contains three types of enzymes:
Trypsin : It converts the protein and peptone into polypeptides and amino acid.
(b) Amylase : It converts the starch into soluble sugar.
(c) Lipase : It converts the emulsified fats into glycerol and fatty acids.
Small Intestine
» Here, the process of digestion completed and absorption of digested foods start.
» From the wall of small intestine, intestinal juices secretes. The following enzymes contain:
(a) Erepsin : It converts the remaining protein and peptone into amino adds.
(b) Maltase : It converts the maltose into glucose.
(c) Sucrase : It converts the sucrose into glucose and fructose.
(d) Lactase : It converts the lactose into glucose and galactose.
(e) Lipase : It converts the emulsified fats into glycerol and fatty adds. Intestinal juice is alkaline in nature.
In a healthy people approximately 2 litres of intestinal juice secretes every day.
3. Absorption
Digested food get mixed into blood is called absorption.
» The absorption of digested foods takes place through villi found in the wall of small intestinal.
4. Assimilation
Use of absorbed food in the body is called assimilation.
5. Defecation
Undigested food reaches into large intestine where bacteria turns it into faeces, which is excreted through anus.