Pancreas

The pancreas is a retroperitoneal organ that serves two functions:

Function

The pancreas produces enzymes that break down all categories of digestible foods.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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 pre-cursor 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 refering to the inactive precursor enzymes).

Related Topics:
Trypsinogen - Chymotrypsinogen - Pancreatic lipase - Amylase - Lumen

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Zymogen granules are localized to the subapical area of pancreatic acinar cells. After fusion with the apical membrane, they are flushed into the duodenum, where enterokinases (bound to enterocytes but facing the lumen of the duodenum) catalyze the activation of trypsinogen into trypsin. Trypsin, an endopeptidase, cleaves amino acids from chymotrypsinogen to produce an active endopeptidase, chymotrypsin. These in turn can 'chop up' polypeptides released from stomach into absorbable units. They also activate the other enzymes released. It is important to synthesize inactive enzymes in the pancreas to avoid autodegradation, which can lead to pancreatitis.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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 from ductal cells contain bicarbonate ions and are alkaline in order to neutralize the acidic chyme that the stomach churns out.

Related Topics:
Bicarbonate ion - Alkaline - Chyme

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Control of the exocrine function of the pancreas are via the enzymes gastrin, cholecystokinin and secretin, 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.

Related Topics:
Gastrin - Cholecystokinin - Secretin - Enzyme - Stomach - Duodenum

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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.

Related Topics:
Trypsinogen - Chymotrypsinogen - Zymogens - Trypsin - Chymotrypsin - Enterokinase - Mucosa

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Endocrine

Embedded throughout the exocrine tissue are small clusters of cells called the Islets of Langerhans, which are the endocrine cells of the pancreas and secrete insulin, glucagon, and several other hormones. The islets contain three major types of cells — alpha cells, beta cells, and delta cells. The largest number of cells are, by far, the beta cells which produce insulin. The alpha cells produce glucagon and the delta cells produce somatostatin, which lead to both decreased glucagon and insulin levels. There are also the PP cells and the D1 cells, about which little is known.

Related Topics:
Islets of Langerhans - Endocrine - Insulin - Glucagon - Alpha cell - Beta cell - Delta cell - Somatostatin - PP cell

~ ~ ~ ~ ~ ~ ~ ~ ~ ~