Plicae

Plicae, from the Latin plica meaning fold, are folds or ridges found in various mucous membranes and tissues. In anatomy, the term commonly refers to permanent folds that increase surface area or modulate luminal flow.

The best known plicae are the plicae circulares of the small intestine (also called folds of Kerckring). These are circular folds formed by mucosa and submucosa that project into the intestinal lumen. They persist along much of the small intestine, being most prominent in the jejunum and gradually diminishing toward the ileum. The plicae host intestinal villi on their mucosal surface, together maximizing absorptive area and aiding in the mixing and slow passage of chyme.

Functionally, plicae increase surface area for absorption and help regulate the rate at which contents move through the gut. By creating folds, they also promote slow mixing, enabling more thorough exposure of nutritional material to the absorptive surface.

Plicae can occur in other mucosal sites as well. In the stomach, folds known as gastric rugae (sometimes referred to as plicae gastricae) expand when the stomach is empty and flatten as it distends; these are not permanent circular folds in the same sense as plicae circulares. Other organs may exhibit regional folds as part of their normal mucosal architecture or in response to physiological or pathological conditions.

Clinically, the appearance and integrity of plicae can be altered by disease that damages mucosa or submucosa, potentially affecting absorption and transport.