Class 11 Biology

Digestion and Absorption


The simple substances; formed after digestion; are absorbed in the jejunum and ileum regions of the small intestine. The undigested and unabsorbed substances go to the large intestine. No significant digestive activity occurs in the large intestine.

Functions of Large Intestine:

Transport of Substances

Transport of water depends upon the osmotic gradient. Active transport is applied to transport various nutrients; like amino acids, monosachharides and electrolytes. Fatty acids and glycerols cannot be absorbed into the blood because they are insoluble. Fatty acids and glycerol are first changed into small droplets; called micelles which move into the intestinal mucosa. The micelles are re-formed into small protein-coated fat globules; called chylomicrons. Chylomicrons are transported into the lymph vessels (lacteals) in the villi). The lymph vessels finally release the absorbed substances into the blood stream.

transverse section of small intestine showing villi

Absorption of substances takes place in different parts of the alimentary canal. But maximum absorption takes place in the small intestine; through villi.


The utilization of nutrients for various activities is called assimilation.


Removal of digestive wastes is called egestion. Egestion of faeces is a voluntary process and is carried out by a mass peristaltic movement.

The Summary of Absorption in Different Parts of Digestive System:


Bacterial or viral infections lead to the inflammation of the intestinal tract. Inflammation is the most common ailment of the intestinal tract. Infections are also caused by tapeworm, roundworm, threadworm, hookworm, pinworm, etc.

Jaundice: Inflammation of liver is called hepatitis. Jaundice is the most common form of hepatitis. Skin and eyes turn yellow due to deposit of bile pigments; in case of jaundice.

Vomiting: Ejection of stomach contents through mouth is called vomiting. This is a reflex action and is controlled by the vomit centre in the medulla.

Diarrhoea: Abnormal frequency of bowel movement and increased liquidity of faecal discharge is called diarrhoea. Absorption of food is reduced in case of diarrhoea.

Constipation: Irregular bowel movements may lead to retention of faeces in the rectum. This condition is called constipation.

Indigestion: A condition in which food is not properly digested and a feeling of fullness prevails is called indigestion.