CECUM

also spelled Caecum, pouch or large tubelike structure in the lower abdominal cavity that receives undigested food material from the small intestine and is considered the first region of the large intestine. It is separated from the ileum (the final portion of the small intestine) by the ileocecal valve (also called Bauhin's valve), which limits the rate of food passage into the cecum and may help prevent material from returning to the small intestine. In humans, the cecum's main functions are to absorb fluids and salts that remain after completion of intestinal digestion and absorption and to mix its contents with a lubricating substance, mucus. The cecum's internal wall is composed of a thick mucous membrane through which water and salts are absorbed. Beneath this lining is a deep layer of muscle tissue that produces churning and kneading motions. The structure and function of the cecum varies in other animals. Vertebrates such as rabbits and horses, which live on a diet composed only of plant life, have a larger cecum that is an important organ of absorption and contains bacteria that help digest cellulose. Animals that eat only meat have a reduced or absent cecum. In cats and dogs, muscle contractions of the cecum are much more vigorous and are reversible. Materials already passed to the next region of the large intestine can be brought back to the cecum for mixing with new food substances. See also appendix.