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The pancreas appears in the fourth week of fetal life from the caudal part of the foregut as dorsal and ventral pancreatic buds. Both anlagen rotate to the right and fuse near the point of origin of the ventral pancreas. Later, as the duodenum rotates, the pancreas shifts to the left. In the adult, only the caudal portion of the head and the uncinate process are derived from the ventral pancreas. The cranial part of the head and all of the body and tail are derived from the dorsal pancreas. Most of the dorsal pancreatic duct joins with the duct of the ventral pancreas to form the main pancreatic duct (duct of Wirsung); a small part persists as the accessory duct (duct of Santorini). In 5%-10% of people, the ventral and dorsal pancreatic ducts do not fuse, and most regions of the pancreas drain through the duct of Santorini and the orifice of the minor papilla. In this case, only the small ventral pancreas drains with the common bile duct through the papilla of Vater.
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The pancreas is a thin elliptic organ that lies within the retroperitoneum in the upper abdomen (Figures 26–1 and 26–2). In the adult, it is 12-15 cm long and weighs 70-100 g. The gland can be divided into three portions—head, body, and tail. The head of the pancreas is intimately adherent to the medial portion of the duodenum and lies in front of the inferior vena cava and superior mesenteric vessels. A small tongue of tissue called the uncinate process lies behind the superior mesenteric vessels as they emerge from the retroperitoneum. Anteriorly, the stomach and the first portion of the duodenum lie partly in front of the pancreas. The common bile duct passes through a posterior groove in the head of the pancreas adjacent to the duodenum. The body of the pancreas is in contact posteriorly with the aorta, the left crus of the diaphragm, the left adrenal gland, and the left kidney. The tail of the pancreas lies in the hilum of the spleen. The main pancreatic duct (the duct of Wirsung) courses along the gland from the tail to the head and joins the common bile duct just before entering the duodenum at the ampulla of Vater. The accessory pancreatic duct (the duct of Santorini) enters the duodenum 2-2.5 cm proximal to the ampulla of Vater (Figure 26–1).
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The blood supply of the pancreas is derived from branches of the celiac and superior mesenteric arteries (Figure 26–2). The superior pancreaticoduodenal artery ...