MOTILITY, ABSORPTION, EGESTION,

 Motility

 When the food enters alimentary canal, it has to be moved forward in a regulated manner from the mouth to anus, so that it can be properly digested and absorbed. These movements are performed by the smooth muscle fibres lining the alimentary tract. Their contractions bring about what is known as motility of the gastro-intestinal tract. Two basic types of movement occur: (1) Mixing movements which keep the juices thoroughly mixed with food and (2) Propulsive movements which move the food forward along the tract at an appropriate rate for digestion and absorption. These movements are popularly known as peristaltic contractions or peristalsis.

Absorption

Major amount of food i.e. more than 90% of digested food and about 10%of water and minerals are absorbed in the small intestine. It is provided with number of special finger-like structures, known as villi. These villi along with smaller divisions, the, microvilli (about 1000 microvilli per villus) help to increase the surface area for absorption. Carbohydrates and proteins are absorbed in blood capillary network (artery and vein) whereas fats or lipids are absorbed in blind –ended lymphatic vessels called as lacteals.

Egestion 

A part of the food is not digested or absorbed by the small intestine. This undigested food moves to the last part of the alimentary canal, the large intestine. The walls of the large intestine absorb water, sodium ions and some vitamins from the food. Therefore, the undigested food-the faecal matter, becomes semi-solid and enters into rectum, where it’s stored for some time and finally expelled out through anus. This act is known as defecation which is caused by the contraction of the rectum and relaxation of anal sphincter.