Pancreas

The pancreas is both an exocrine and an endocrine gland, so it plays key roles in digestion and metabolism.

It is a retroperitoneal organ (except for its tail, which is intraperitoneal). It lies obliquely along the posterior abdominal wall at the level of the L1-L2 vertebrae. The tail extends to the T12 vertebral level.

Gross anatomy and relations

The pancreas is divided into a head, uncinate process, neck, body, and tail.

• Head: Lies in the C-shaped concavity of the duodenum.
• Uncinate process: A hook-like projection from the inferior part of the head. It lies behind the superior mesenteric vessels and in front of the abdominal aorta.
• Neck: The portal vein lies behind the neck.
• Body:
  • The splenic artery runs along the superior margin of the body.
  • The splenic vein runs in close proximity to the posterior surface.
• Tail: Narrow and lies in the splenorenal ligament.

Pancreatic ducts

• Main pancreatic duct (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.
• Accessory pancreatic duct (duct of Santorini): Starts at the lower part of the head and opens proximal to the main pancreatic duct at the minor duodenal papilla.

Histology

Histologically, the pancreas contains acini and islets of Langerhans.

Acini (exocrine pancreas)

• The acini consist of exocrine cells arranged in a lobular fashion around a central lumen.
• Acinar cells have deeply basophilic cytoplasm because they are rich in rough endoplasmic reticulum, with zymogen granules at the apex of the cell.
• Each lobule is drained by its own ductule. These ductules merge to form intralobular and interlobular ducts, which then drain into the main pancreatic duct.
• Acinar cells secrete enzymes such as trypsinogen, lipase, amylase, and chymotrypsinogen.
• The cells lining the ducts secrete bicarbonate.

Islets of Langerhans (endocrine pancreas)

• Clusters of islet cells are interspersed between the acini.
• The islets are supplied by arterioles that branch into a network of fenestrated capillaries. Hormones are secreted into these capillaries 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.

Blood supply, lymphatic drainage, and innervation

• Arterial supply: Branches from the celiac trunk and SMA.
  • Head is supplied by the superior and inferior pancreaticoduodenal arteries.
  • Neck, body, and tail are supplied by the splenic artery.
• Venous drainage: To the splenic, superior mesenteric, and portal veins.
• Lymphatic drainage:
  • 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: By the celiac plexus. Spinal segments T 7-11 innervate the pancreas.