Nutrition and Digestion: Absorption of Nutrients, Mouth, Stomach, Small and Large Intestine, Assimilation and Egestion (For CBSE, ICSE, IAS, NET, NRA 2022)

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Absorption of Nutrients

Some absorption occurs in the mouth itself, some in the stomach but most absorption occurs in the intestine.

In Mouth

Mouth absorbs water soluble vitamins, simple sugar like glucose and water.

In Stomach

Some water, certain ions and minerals, glucose and such drugs as aspirin and ethanol are absorbed from the stomach into the blood. This absorption occurs by osmosis, diffusion and active transport.

Small Intestine

  • Absorption of disaccharides, peptides, fatty acids and monoglycerides substances occurs in the villi, which line the inner surface of the small intestine.
  • Products absorbed into the blood capillaries of the villi are amino acids and monosaccharides (glucose, fructose and galactose) .
  • The individual epithelial cells also have finger-like projections of plasma membrane are called known as microvilli and is further increase the absorptive surface.
  • Products absorbed into the lacteals (lymph vessels) of the villi are fatty acids and glycerol.
  • A nutrient absorbed into the blood is carried by veins into the liver, and the nutrient absorbed by the lacteals (small lymph vessels) enters the lymphatic system.
Image Showing Microscopic Structure of a Part of the Wall of …

Large Intestine

Large intestine absorbs some nutrients while also removing water and absorbs wastes. Colon which is the major portion of large intestine is responsible for absorbing water back into body.


  • The conversion of absorbed food in complex substances such as proteins and vitamins required by body is called assimilation.
  • After absorption from the food canal the digested food is assimilated by the body in the following ways:
    • Fatty acids and glycerol ate again converted into fats which are stored in the adipose tissue.
    • Sugar is converting into a complex polysaccharide, glycogen in the liver. This stored glycogen is metabolized and utilized during conditions of stress.
    • The amino acids absorbed from the intestine are utilized to synthesis various types of proteins in the body. The body needs to synthesis various proteins and various types of enzymes.
    • The excess amino acids cannot be stored by the body and needs to be deaminated in the liver and be converted into urea which is then removed from the blood by the kidneys and excreted.

Egestion (Defecation)

The elimination of undigested remains of food from the alimentary canal is called egestion or defecation. The waste material egested out from the anus is called feces or stool.

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