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.
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 pancreaticoduodenal 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 duodenum and pancreas (stomach removed). |
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 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.
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.
*
Benign tumours*
Carcinoma of pancreas (pancreatic cancer)*
Cystic fibrosis*
Diabetes*
Exocrine pancreatic insufficiency*
Pancreatitis**
Acute pancreatitis**
Chronic pancreatitis*
Pancreatic pseudocystThe 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.
*
Pancreas transplantationhttp://www.randomhouse.com/wotd/index.pperl?date=20010222 Review 2005-03-10
