Pancreas

The pancreas is an exocrine and endocrine gland with pivotal roles in digestion and metabolism. It is a retroperitoneal organ ( except for its tail which is intraperitoneal), situated obliquely along the posterior abdominal wall at the level of L1-2 vertebra. The tail extends to T12 vertebral level. It is divided into a head, uncinate process, neck, body and tail. The head of the pancreas lies in the C shaped concavity of the duodenum. The uncinate process is a hook-like- projection from the inferior part of the head and it lies behind the superior mesenteric vessels and in front of the abdominal aorta. The portal vein lies behind the neck. The splenic artery runs along the superior margin of the body of the pancreas. The splenic vein runs in close proximity to the posterior surface of the pancreas. The narrow tail of the pancreas lies in the splenorenal ligament. The main pancreatic duct or the duct of Wirsung runs along the entire length of the pancreas. It joins the common bile duct to form the hepatopancreatic ampulla just before opening into the major duodenal papilla in the second part of the duodenum. The accessory pancreatic duct of Santorini starts at the lower part of the head and opens proximal to the main pancreatic duct, at the minor duodenal papilla.

Histologically, the pancreas shows acini and islets of Langerhans. The acini consist of exocrine cells arranged in a lobular fashion around a central lumen. The acinar cells have a deeply basophilic cytoplasm being rich in rough endoplasmic reticulum with zymogen granules at the apex of the cell. Each lobule is drained by its own ductule which merges with other ductules to form intralobular and interlobular ducts that then drain into the main pancreatic duct. The acinar cells secrete enzymes like trypsinogen, lipase, amylase, chymotrypsinogen etc. The cells lining the ducts secrete bicarbonate. Clusters of islet cells are interspersed in between the acini. The islets are supplied by arterioles that branch into a network of fenestrated capillaries into which the hormones are secreted and collected by the draining vein. They show mainly three types of cells -

1. Alpha cells: They secrete glucagon.

2. Beta cells: They are the major cells in the islets. They secrete Insulin.

3. Delta cells: They secrete somatostatin and pancreatic gastrin.

The pancreas is supplied by branches from the celiac trunk and SMA. Head is supplied by superior and inferior pancreaticoduodenal arteries. Neck, body and tail are supplied by the splenic artery. Venous drainage is to the splenic, superior mesenteric and portal veins. Head and body drain to the pyloric and pancreaticosplenic lymph nodes and finally into the pre-aortic nodes. Tail drains into the splenic nodes. Nerve supply is by the celiac plexus. Spinal segments T 7-11 innervate the pancreas.