Blood Supply and Innervation of the Pancreas
The pancreas is a unique abdominal organ in that it is classified as both endocrine and exocrine in function. It is situated posterior to the stomach and is supported by the floor of the lesser sac or omental bursa. It is a retroperitoneal visceral tissue mass, save its tail which communicates with the right aspect of the spleen. Macroscopically, it is theoretically divided into four main parts running from the midline to the left side of the body and includes the head, neck, body and tail in that order. The head is partially encompassed by the c-shaped curvature of the proximal part of the duodenum and its uncinate process stabilizes it because it is wedged between the duodenum and the superior mesenteric vessels, which lie slightly anterior to this tissue convexity. The neck is bordered posteriorly by the superior mesenteric vessels, as the pancreas veers anteriorly towards its tail and is situated just inferior to the pylorus of the stomach. The body of the pancreas points cranially and stretches over the duodenojejunal flexure as well as the superior aspect of the left kidney. Lastly and most laterally, the tail of the pancreas forms its apex at the hilum of the spleen within the splenorenal ligament.
Histologically, the pancreas contains many different cells that are responsible for the multiple metabolic functions that the pancreas must perform. These digestive mechanisms are essential for the breakdown and absorption of nutrients acquired from the dietary intake of food and without them healthy sustenance would be almost impossible. The exocrine pancreas is comprised of the acinar and pancreatic ductal cells. The acinar cells secrete various substances which process proteins, starches and fats. The pancreatic ductal cells secrete bicarbonate ion in a fluid which helps neutralize the acidic chyme that is dumped by the stomach into the duodenum. The endocrine pancreas is made up of the islets of langerhans which secrete various hormones such as insulin, glucagon and somatostatin. Pancreatic secretion is governed by both the vagus nerve (CN X) and the hormones secretin and cholecystokinin.
The main vascular supply of the pancreas is governed by the splenic artery and its subsequent branches, which stem from the celiac trunk of the aorta at the level of the twelfth thoracic vertebra. It also receives blood from the superior mesenteric artery, the gastroduodenal artery and also the superior and inferior pancreaticoduodenal arteries.
Venous and Lymphatic Drainage
The venous drainage of the pancreas occurs mainly by the splenic vein, which merges with the superior mesenteric vein and enters the liver as the portal vein. Some branches however communicate directly with the superior mesenteric vein and thus a loop of venous drainage utilising both sets of venous plexuses occurs.
The lymphatic drainage of the pancreas allows the lymphatic fluid that it produces to run in the tiny networks that sit on the blood vessels supplying the area and collect in the pancreaticosplenic nodes which are found sitting along the splenic artery. These drain into the celiac lymphatic plexus and from there either indirectly into the thoracic duct via the cisterna chyli or directly into it depending on the presence of the sac.
The nervous supply of the pancreas is comprised of three different nerve bundles including the vagus nerve (CN X), the thoracic splanchnic nerves fibers from the superior mesenteric and celiac plexuses.