Through which duct do pancreatic enzymes enter the duodenum, and which cells secrete bicarbonate to neutralize chyme?

• A. Sphincter of Oddi; centroacinar cells
• B. Common bile duct; acinar cells
• C. Pancreatic duct; acinar cells
• D. Pancreatic duct; ductal and centroacinar cells

Answer: (D)

Pancreatic enzymes enter the duodenum through the pancreatic duct, which channels the enzyme-rich juice from the acini to the duodenum (flow is regulated as it passes the sphincter of Oddi). The bicarbonate that neutralizes the incoming chyme is secreted by the ductal component of the pancreas—ductal cells lining the ducts and the centroacinar cells at the start of the duct system—producing a bicarbonate-rich fluid that raises pH for optimal enzyme activity. Acinar cells make the digestive enzymes themselves but aren’t responsible for bicarbonate secretion. That combination of pancreatic duct delivery and bicarbonate secretion from ductal and centroacinar cells best fits the physiology.