The colon and the rectum are the final portions of the tube that extends from the mouth to the anus. Food enters the mouth where it is chewed and then swallowed. It then travels through the esophagus and into the stomach. In the stomach, the food is ground into smaller particles and then enters the small intestine in a carefully controlled manner. In the small intestine, final digestion of food and absorption of the nutrients contained in the food occurs. The food that is not digested and absorbed enters the large intestine or colon and finally the rectum. The large intestine is about six feet long and acts primarily as a storage facility for waste; however, additional water, salts, and some vitamins are further removed. In addition, some of the undigested food, for example, fiber, is digested by colonic bacteria and some of the products of digestion are absorbed from the colon and into the body. (It is estimated that 10% of the energy derived from food comes from these products of bacterial digestion in the colon.) The remaining undigested food, dying cells from the lining of the intestines, and large numbers of bacteria are stored in the colon and then periodically passed into the rectum. Their arrival into the rectum initiates a bowel movement that empties the colonic contents from the body as stool.