Discuss mechanisms of absorption.

Explanation

Mechanism of absorption for different molecules is as follow
(i) Small amounts of monosaccarides like glucose, amino acids and some electrolytes like chloride ions are generally absorbed by simple diffusion. The passage of these substances into the blood depends upon the concentration gradient
(ii) 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) Fatty acids and glycerol being insoluble, cannot be absorbed into the blood. They are first incorporated into micelles (small droplets) which move into intestinal mucosa.
Further, they are reformed into protein coated fat globules called chylomicrons which are transported to the lymph vessels in the villi. These lymph vessels ultimately release the absorbed substances into the blood stream.