Pancreas
The pancreas is an organ in the digestive system that serves two major functions:
- exocrine - producing pancreatic juice containing digestive enzymes.
- endocrine - producing several important hormones, including insulin.
Anatomy
The pancreas is located posterior to the stomach and in close association with the duodenum.
In humans, the pancreas is a 6-10 inch elongated organ in the abdomen located retroperitoneal. It is often described as having three regions: 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.
The pancreas is supplied arterially by the pancreaticoduodenal arteries, themselves branches of the superior mesenteric artery or of the hepatic artery (branch of celiac trunk from the abdominal aorta). The superior mesenteric artery provides the inferior pancreaticoduodenal arteries while the gastroduodenal artery (one of the terminal branches of the hepatic artery) provides the superior gastroduodenal 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).
Function
The pancreas produces enzymes that break down all categories of digestible foods (exocrine pancreas) and secretes hormones that affect carbohydrate metabolism (endocrine pancreas).
Exocrine
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 precursor digestive enzymes (mainly trypsinogen, chymotrypsinogen, pancreatic lipase, and amylase) that are secreted into the lumen of the acinus. These granules are termed zymogen granules (zymogen referring to the inactive precursor enzymes). It is important to synthesize inactive enzymes in the pancreas to avoid autodegradation, which can lead to pancreatitis.
The pancreas is near the liver, and is the main source of enzymes for digesting fats (lipids) and proteins - the intestinal walls have enzymes that will digest polysaccharides. Pancreatic secretions from ductal cells contain bicarbonate ions and are alkaline in order to neutralize the acidic chyme that the stomach churns out. Control of the exocrine function of the pancreas are via the hormones gastrin, cholecystokinin and secretin, which are hormones 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 which the pancreas secretes 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 importance of its enzyme contents, injuring the pancreas is a very dangerous situation. A puncture of the pancreas tends to require careful medical intervention.
Endocrine
Scattered amongst the acini are the endocrine cells of the pancreas, in groups called the islets of Langerhans. They are:
- Insulin-producing beta cells (50-80% of the islet cells)
- Glucagon-releasing alpha cells (15-20%)
- Somatostatin-producing delta cells (3-10%)
- Pancreatic polypeptide-containing PP cells (
The islets are a compact collection of endocrine cells arranged in clusters and cords and are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of endocrine cells in direct contact with vessels, and most endocrine cells are in direct contact with blood vessels, by either cytoplasmic processes or by direct apposition.
Edibility
Pancreas comes from the Greek pankreas (a combination of pan and kreas) which means 'all meat'. Kreas in Homeric literature meant edible animal flesh. An example of one such food that can be made from the pancreas of a calf, lamb or pig is sweetbread.
Diseases of the pancreas
- Benign tumours
- Carcinoma of pancreas (pancreatic cancer)
- Cystic fibrosis
- Diabetes
- Exocrine pancreatic insufficiency
- Pancreatitis
- Pancreatic pseudocyst
History
The pancreas was discovered by Herophilus (335-280 BC), a Greek anatomist and surgeon. Only a few hundred years before, Ruphos, another Greek anatomist, gave the pancreas its name.
See also
References
http://www.randomhouse.com/wotd/index.pperl?date=20010222 Review 2005-03-10