The pancreas comprises the head, uncinate process, neck, body and tail. The head lies within, and closely attached to, the ‘C’ of the duodenum. The main pancreatic duct (Wirsung) runs the length of the gland. It usually joins the common bile duct at the ampulla of Vater to enter the second part of the duodenum at the duodenal papilla. The accessory duct (Santorini) opens into the duodenum proximal to the main duct. The gland is lobulated and produces the exocrine secretion of digestive hormones from serous-secreting cells, arranged in alveoli. Between these lie the islets of Langerhans, containing A cells (glucagons), B cells (insulin) and D cells (gastrin and somatostatin). The arterial supply is via the splenic artery, and the superior and inferior pancreaticoduodenal arteries. Corresponding veins drain into the portal system. The splenic artery is characteristically tortuous and runs along the upper border of the pancreas; the vein lies behind the gland.
Embryologically, the pancreas derives from a large dorsal diverticulum from the duodenum and a small ventral bud from the side of the bile duct. The ventral bud swings posteriorly to fuse with the dorsal, trapping the superior mesenteric vessels between and forming the uncinate process. The ducts of the two buds then communicate, that of the ventral bud takes over the main duct, leaving the original duct of the larger dorsal bud as the accessory duct.