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The pancreas is a retroperitoneal organ located posterior to the stomach on the posterior abdominal wall .
In humans the pancreas is a small elongated organ in the abdomen. It is described as having a head, body and tail. The pancreatic head abuts the second part of the duodenum while the tail extends towards the spleen. The pancreatic duct runs the length of the pancreas and empties into the second part of the duodenum at the ampulla of Vater. The common bile duct commonly joins the pancreatic duct at or near this point.
It is supplied arterially by the pancreaticoduodenal arteries , themselves branches of the superior mesenteric artery . Venous drainage is via the pancreaticoduodenal veins which end up in the portal vein. The splenic vein passes posterior to the pancreas but is said to not drain the pancreas itself. The portal vein is formed by the union of the superior mesenteric vein and splenic vein posterior to the body of the pancreas. In some people (some books say 40% of people), the inferior mesenteric vein also joins with the splenic vein behind the pancreas (in others it simply joins with the superior mesenteric vein instead).
The pancreas is covered in a tissue capsule that partitions the gland into lobules. The bulk of the pancreas is composed of pancreatic exocrine cells, whose ducts are arranged in clusters called acini (singular acinus). The cells are filled with secretory granules containing the digestive enzymes (mainly trypsin, chymotrypsin, pancreatic lipase , and amylase) that are secreted into the lumen of the acinus.
The pancreas is the main source of enzymes for digesting fats (lipids) and proteins - the intestinal walls have enzymes that will digest polysaccharides. Pancreatic secretions contain bicarbonate ion s and are alkaline in order to neutralize the acidic chymeChyme is the liquid substance found in the stomach before passing the pyloric valve and entering the duodenum. It consists of partially digested food, water, hydrochloric acid, and various digestive enzymes. Chyme slowly passes through the pyloric valve a that the stomach churns out.
Control of the exocrine function of the pancreas are via the enzymes gastrinIn humans, gastrin is a hormone that stimulates secretion of gastric acid by the stomach. Synthesis Gastrin is a linear peptide hormone secreted into the blood by G cells that are located mainly in the pylorus of the stomach. Gastrin is found primarily in, cholecystokininCholecystokinin CCK previously pancreozymin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. CCK is secreted by the duodenum, the first segment of the small intestine, and causes the release and secretinSecretin is a hormone produced in the S cells of the duodenum in response to low duodenum pH and fatty acids in the duodenum to signal the secretion of bicarbonate from bicarbonate producing organs( liver, pancreas, Brunner's glands) when the pH drops bel, which are enzymes secreted by cells in the stomach and duodenum, in response to distension and/or food and which cause secretion of pancreatic juices.
The two major proteases the pancreas excretes are trypsinogen and chymotrypsinogen. These zymogens are inactivated forms of trypsin and chymotrypsin. Once released in the intestine, the enzyme enterokinase present in the intestinal mucosa activates trypsinogen by cleaving it to form trypsin. The free trypsin then cleaves the rest of the trypsinogen and chymotrypsinogen to their active forms.
Pancreatic secretions accumulate in intralobular ducts that drain to the main pancreatic duct, which drains directly into the duodenum.
Due to the potency of its enzyme contents, it is a very dangerous organ to injure and a puncture of the pancreas tends to require careful medical intervention.