(a) Human alimentary canal diagram:

(b) The small intestine is the most important part of the digestive system. Maximum absorption occurs in the small intestine because of the following reasons:
(i) Digestion is completed in the small intestine because the inner lining of the small intestine is provided with villi which increase the surface area for absorption of digested food.
(ii) Wall of the intestine is richly supplied with blood vessels which assimilate the absorbed food to the other parts of the body.