Overview

Normal diameter (head)≤≈3 mm

The main pancreatic duct (of Wirsung) begins in the tail and runs through the body and neck near the posterior surface, receiving small tributaries in a "herring-bone" pattern. In the head it turns downwards and backwards to meet the bile duct in the duodenal wall at the hepatopancreatic ampulla on the major duodenal papilla. It is normally up to about 3 mm wide in the head and tapers towards the tail.

The accessory pancreatic duct (of Santorini) drains the anterosuperior head. It opens on the minor duodenal papilla, about 2 cm proximal to the major papilla, and often communicates with the main duct.

The duct tree begins at the centroacinar cells and continues as intercalated, intralobular and interlobular ducts. Duct epithelium secretes HCO₃⁻ using CFTR and Cl⁻/HCO₃⁻ exchangers (SLC26A6) when stimulated by secretin, through cAMP. Bicarbonate can reach about 140 mmol/L in the juice at high flow.

Location: Within the pancreas, from tail to head, ending at the major (main duct) and minor (accessory duct) duodenal papillae in the 2nd part of the duodenum.

Anatomy

Histology: Intercalated ducts are lined by low cuboidal cells that begin inside the acinus as centroacinar cells. The larger ducts have columnar epithelium with goblet cells and a fibrous wall.

Function

Carry pancreatic juice to the duodenum.
Duct cells secrete the bicarbonate-rich, watery fraction of pancreatic juice.

Clinical significance

Ductal obstruction

Stones (chronic pancreatitis), strictures and tumours dilate the duct. The double-duct sign, with both bile and pancreatic ducts dilated, suggests a pancreatic head or ampullary tumour. Intraductal papillary mucinous neoplasm (IPMN) is a premalignant cystic lesion of the duct system.

Cystic fibrosis

Defective CFTR reduces ductal fluid and HCO₃⁻ secretion. Protein-rich secretions block the ducts, activate enzymes and destroy the gland, causing exocrine insufficiency in about 85–90% of patients with CF.

Test yourself

Which hormone is released from duodenal S cells when duodenal pH falls below about 4.5, and stimulates bicarbonate secretion by pancreatic ducts?

Cholecystokinin
Gastrin
Motilin
Secretin

Answer: Secretin

Secretin ("nature's antacid") drives watery, HCO₃⁻-rich pancreatic and biliary secretion through cAMP and CFTR, and it inhibits gastrin and acid secretion. CCK, from I cells and triggered by fat and amino acids, mainly stimulates enzyme secretion and gallbladder contraction.