Papilla of Vater: structure and function.

The papilla of Vater is involved in the regulation of bile flow (inhibition and facilitation) into the duodenum and the prevention of reflux into the bile and pancreatic duct system. These functions are achieved by a special muscular, neural and mucosal structure of the papilla of Vater. The mucosa of the papilla of Vater consists of a complicated system of mucosal folds which can function as an anti-reflux valve or might even participate in the regulation of bile outflow. The smooth muscle of the sphincter of Oddi differs anatomically and embryologically from the surrounding duodenal muscle. It shows spontaneous electrical and mechanical activity acting independently from the duodenum but integrated into the overall function of the gastrointestinal tract by myogenic mechanisms, extrinsic and intrinsic nerves and circulating hormones. A spontaneous myogenic electrical activity propagates distally and leads to distally propagating phasic contractions. With endoscopic manometry in humans these phasic contractions as well as basal tone, bile duct pressure and pancreatic duct pressure can be measured. Changes of the basal tone and the phasic activity will alter the flow resistance thus regulating bile flow and inducing gallbladder filling. The most characteristic feature of the sphincter of Oddi is the inhibitory effect of cholecystokinin, which is a powerful contractor of the gallbladder, on the sphincter of Oddi motor activity. Cholecystokinin released in response to intra-duodenal fat and other nutrients might be the physiological stimulus of the increased bile flow post-prandially. The function of other hormones is still rather speculative and their physiological significance awaits further confirmation.