Discuss mechanisms of absorption.

The absorption of digested food happens through passive, active or facilitated transport mechanism.

Mechanism of absorption for different molecules is as follow

(i) Simple Diffusion: Small amounts of monosaccharide like glucose, amino acids and some electrolytes like chloride ions are absorbed by simple diffusion. The passage of these substances into the blood depends upon the concentration gradient

(ii) Facilitated Transport: Fructose and some amino acids are absorbed with the help of carrier ions like Na⁺. This mechanism of transport is called facilitated transport or active transport.

(iii) Transport of water depends on osmotic gradient.

(iv) Transport of Fatty acids and glycerol: As these substances are insoluble, they cannot be absorbed into the blood. They are first converted into micelles (smalll droplets) which move into intestinal mucosa. Here these micelles are coverted into very small protein-coated fat globules called chylomicrons which are transported to the lymph vessels in the villi. These lymph vessels release the absorbed substances into the blood stream.