pancreatic duct

The main pancreatic duct runs the length of the pancreas from tail to head, collecting secretions from smaller intralobular and interlobular ducts. It usually unites with the common bile duct to form the hepatopancreatic ampulla (ampulla of Vater), which empties into the second part of the duodenum through the major duodenal papilla, regulated by the sphincter of Oddi. An accessory pancreatic duct (duct of Santorini) may drain separately into the minor duodenal papilla, proximal to the major papilla; in some individuals, the accessory duct is the dominant drainage pathway (pancreas divisum), which can predispose to recurrent pancreatitis due to inadequate drainage through the smaller papilla.

Physiologically, ductal epithelial cells secrete bicarbonate-rich fluid in response to secretin, neutralizing acidic chyme entering the duodenum, while acinar cells secrete digestive enzymes (amylase, lipase, proteases) in response to CCK, which also stimulates gallbladder contraction and enzyme secretion. Enzymes are usually secreted as inactive zymogens (e.g., trypsinogen) to prevent autodigestion; trypsinogen is activated to trypsin by duodenal enteropeptidase, which then activates other zymogens.

Clinically, obstruction of the pancreatic duct (by gallstones, tumors such as pancreatic adenocarcinoma, strictures, or pancreas divisum) can cause backflow of enzymes, premature enzyme activation, and acute or chronic pancreatitis. Gallstone impaction at the ampulla of Vater is a classic cause of gallstone pancreatitis due to shared drainage with the common bile duct. Chronic pancreatitis often shows a dilated, beaded ("chain of lakes") pancreatic duct on imaging (ERCP or MRCP). Pancreatic ductal adenocarcinoma, arising from ductal epithelium, is the most common pancreatic malignancy and often presents with painless jaundice if located in the head of the pancreas, due to obstruction of the common bile duct as it passes through the pancreatic head.