Continued from: Digestive diet. How it works. Part II
The walls of the small intestine look and feel like velvet. It is lined with hundreds of thousands of hair-like nodules called villi which contain tiny blood vessels. T hey increase the surface area of the small intestine so that the nutrients in the chyme can be easily absorbed by the bloodstream and carried to the liver for storage. A further feature of the villi is their constant motion, which progressively moves the food along the intestinal tract. In this manner, food is allowed to come into contact with the different types of enzymes secreted by small glands which are also embedded in the intestinal walls. These enzymes include lactose, maltose, enterokose and sucrose, all having various functions to perform. Minerals and vitamins are also absorbed into the body from the small intestine.
In the intestinal walls are various muscles which relax and contract when stimulated by special nerves during what is termed intestinal peristalsis. During the digestion process, the small intestine is in constant motion under the action of this peristalsis and the food is progressively moved along the intestinal tract and brought into contact with the enzymes and villi.
The term small intestine is confusing for the total length is over six meters. The word small refers to the smaller diameter when compared to the large intestine, which is only one and a half meters long. Food must traverse the whole length of the small intestine undergoing great changes and having the bulk of its nutrients absorbed into the bloodstream.
The chyme completes its journey through the small intestine and passes into the large intestine by way of the ileocecal valve. This valve regulates the flow of the chyme to the large intestine by preventing the small intestine emptying too quickly. At the same time it prevents any chyme from going back into the small intestine. At the point of entering the large intestine, the chyme contains mainly waste products (undigested food) and water. The water is largely absorbed in the large intestine to prevent dehydration of the body. The remaining waste matter proceeds to the rectum where it is eliminated from the body in the form of stool. This completes the process of digestion.