The descending part (also the 2nd part) is about 7-10 cm long, located entirely retroperitoneal. It begins to the right of the IVC, descends along the right side of the L1-L3, and curves around the head of the pancreas.

Features of the descending part are:

• Hepatopancreatic ampulla (ampulla of Vater) - space formed by the union of the common bile duct and main pancreatic duct close to the duodenal wall on the left side (medially);

• Hepatopancreatic sphincter (of Oddi) - smooth muscle in the wall of the duodenum that regulates the flow of bile and pancreatic juice into the second part of the duodenum;

• Major duodenal papilla (of Vater) - grossly visible luminal projection from the ampulla of Vater, with its opening into the left side of the second part of the duodenum;

• Minor duodenal papilla - accessory or minor pancreatic duct (of Santorini) entering duodenum superior to the major papilla (not always present).