large intestine

The large intestine forms an upside down U over the coiled small intestine. It begins at the lower right-hand side of the body and ends on the lower left-hand side. The large intestine is about 5-6 feet long. It has three parts: the cecum, the colon, and the rectum. The cecum is a pouch at the beginning of the large intestine. This area allows food to pass from the small intestine to the large intestine. The colon is where fluids and salts are absorbed and extends from the cecum to the rectum. The last part of the large intestine is the rectum, which is where feces (waste material) is stored before leaving the body through the anus.

The main job of the large intestine is to remove water and salts (electrolytes) from the undigested material and to form solid waste that can be excreted. Bacteria in the large intestine help to break down the undigested materials. The remaining contents of the large intestine are moved toward the rectum, where feces are stored until they leave the body through the anus as a bowel movement.



the functions of large intstine are as fool ows

The large intestine performs several important functions in digestion. Its main functions are:

Absorbing water

Completing the process of digestion that largely takes place in the small intestine. It takes nearly 24 to 30 hours to complete the digestive process. Further digestion or breaking down of nutrients does not take place here but it helps by absorbing water and making the stools solid.

Absorption of vitamins

The large intestine also helps in absorption of vitamins made by bacteria that normally live in the large intestine. These are friendly bacteria called commensal bacteria. There are over 700 species of bacteria that perform a variety of functions.

These commensal bacteria breakdown the undigested polysaccharides or fibers in diet into short-chain fatty acids. These can be absorbed by the large intestine by passive diffusion. The bacteria also produce gas (flatus), which is a mixture of nitrogen and carbon dioxide, with small amounts of the gases hydrogen, methane, and hydrogen sulphide. These result from the bacterial fermentation of undigested polysaccharides.

These bacteria also produce large amounts of vitamins. The most important of these is Vitamin K and Biotin (a B vitamin). When the vitamin intake in diet is low, this can be an important source of these vitamins. A person who depends on absorption of vitamins formed by bacteria in the large intestine may become vitamin deficient if treated with drugs like antibiotics that kill the commensal bacteria.

Reducing acidity and protecting from infections

The mucosa of the large intestine also secretes bicarbonates to neutralise the increased acidity resulting from the formation of these fatty acids and other digestive components at earlier parts of the intestines.

The mucosal layer of the large intestine also acts as a mucosal barrier and protects from microbial infections and invasions.

Producing antibodies

The large intestine, particularly the appendix, is a confluence of several lymphoid tissues. These play an important role in immunity. The lymphoid tissues of the large intestine also help in the production of antibodies and cross reactive antibodies. These antibodies are produced by the immune system against the normal commensal bacteria but may also be active against related harmful bacteria and thus prevent infections.