PLICA CIRCULARIS

plural Plicae Circulares, also called Valve Of Kerckring, any of the crescent or circular folds in the surface of the small-shaped intestine that triple its absorption area, slow down the passage of food, and give it a characteristically pleated appearance. The folds usually run one-half to two-thirds of the way around the inside of the intestinal wall; occasionally, a single fold may spiral the wall for three or four complete turns. The folds are largest and most prevalent in the beginning of the intestinal tract; toward the middle they are more widely spaced and shortened, and near the end they totally disappear. The tissue that forms these structures is the surface mucous-membrane lining and the deeper submucosa. The mucous membrane further divides into small projections called villi (q.v.) and is the predominant site of nutritional absorption, while the submucosa is composed of supportive tissue and blood vessels. Unlike the transient folds in the stomach, these intestinal folds are permanent structures not obliterated by distention.