The sphincter of Oddi regulates flow of bile (and pancreatic juice) into the duodenum. It consists of:

The human sphincter of Oddi is about 10-15 mm in length, situated within the muscular layer of the media of the duodenum. It consists of three distinct segments: Sphincter choledochus, Sphincter pancreaticus, and Ampullary sphincterThe choledochal sphincter covers the distal end of the intraduodenal pa of the common bile duct before it joins with the pancreatic duct (duct of Wirsung). The pancreatic sphincter is located at the distal end of the pancreatic duct. The ampullary sphincter covers the distal end of both ducts. The term "sphincter of Oddi" refers to all three sphincters. Ref: Nuclear Hepatology: A Textbook of Hepatobiliary Diseases By Gerbail T. Krishnamuhy, Shakuntala Krishnamuhy, 2009, Page 184.