Relaxation of the sphincter of Oddi in response to a meal is largely under the control of which hormone?a. Gastrin
The sphincter of Oddi is a complex structure that is functionally independent from the duodenal musculature and creates a high-pressure zone between the bile duct and the duodenum. The sphincter of Oddi is about 4 to 6 mm in length and has a basal resting pressure of about 13 mm Hg above the duodenal pressure. On manometry, the sphincter shows phasic contractions with a frequency of about 4/min and an amplitude of 12 to 140 mm Hg. The spontaneous motility of the sphincter of Oddi is regulated by the interstitial cells of Cajal through intrinsic and extrinsic inputs from hormones and neurons acting on the smooth muscle cells. Relaxation occurs with a rise in cholecystokinin (CCK), leading to diminished amplitude of phasic contractions and reduced basal pressure, allowing increased flow of bile into the duodenum. During fasting, the sphincter of Oddi activity is coordinated with the periodic partial gallbladder emptying and an increase in bile flow that occurs during phase II of the migrating myoelectric motor complexes.