Which sphincter controls the entry of bile and pancreatic juice into the duodenum?

• A. Pyloric sphincter
• B. Ileocecal valve
• C. Cardiac sphincter
• D. Sphincter of Oddi

Answer: (D)

The mechanism being tested is how bile and pancreatic juice enter the duodenum and what valve controls that flow. The Sphincter of Oddi is the muscular ring around the junction where the common bile duct and the pancreatic duct meet the duodenum (the major duodenal papilla). When it relaxes, bile and pancreatic secretions flow into the duodenum to aid digestion; when it contracts, those secretions are prevented from entering the intestine. This relaxation is stimulated by signals such as cholecystokinin after a meal, coordinating digestion.

In contrast, the pyloric sphincter sits at the stomach’s exit and regulates chyme entering the duodenum, the cardiac sphincter (lower esophageal sphincter) prevents reflux into the esophagus, and the ileocecal valve controls passage between the ileum and cecum. None of these regulate bile and pancreatic juice entry into the duodenum, making the Sphincter of Oddi the correct choice.