PANCREASE

                                                                 PANCREAS

The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as an exocrine gland, secreting pancreatic juice containing digestive enzymes that pass to the small intestine. These enzymes help to further break down the carbohydrates, proteins, and fats in the chyme.

Function

The pancreas is a dual-function gland, having features of both endocrine and exocrine glands.

Endocrine

The part of the pancreas with endocrine function is made up of approximately a million^[3] cell clusters called islets of Langerhans. Four main cell types exist in the islets. They are relatively difficult to distinguish using standard staining techniques, but they can be classified by their secretion: α cells secrete glucagon (increase glucose in blood), β cells secrete insulin (decrease glucose in blood), δ cells secrete somatostatin (regulates/stops α and β cells), and PP cells secrete pancreatic polypeptide.[4]

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. According to the volume The Body, by Alan E. Nourse, the islets are "busily manufacturing their hormone and generally disregarding the pancreatic cells all around them, as though they were located in some completely different part of the body."

Exocrine pancreas

The exocrine pancreas has ducts that are arranged in clusters called acini (singular acinus). Pancreatic secretions are secreted into the lumen of the acinus, and then accumulate in intralobular ducts that drain to the main pancreatic duct, which drains directly into the duodenum.
Control of the exocrine function of the pancreas is 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.
There are two main classes of exocrine pancreatic secretions:

Secretion	Cell producing it	Primary signal
bicarbonate ions	Centroacinar cells	Secretin
digestive enzymes	Basophilic cells	CCK

Pancreatic secretions from ductal cells contain bicarbonate ions and are alkaline in order to neutralize the acidic chyme that the stomach churns out.
The pancreas is also the main source of enzymes for digesting fats (lipids) and proteins. (The enzymes that digest polysaccharides, by contrast, are primarily produced by the walls of the intestines.)
The cells are filled with secretory granules containing the precursor digestive enzymes. The major proteases which the pancreas secretes are trypsinogen and chymotrypsinogen. Secreted to a lesser degree are pancreatic lipase and pancreatic amylase. The pancreas also secretes phospholipase A2, lysophospholipase, and cholesterol esterase.

It is important to synthesize inactive enzymes in the pancreas to avoid autodegradation, which can lead to pancreatitis. These granules are termed zymogen granules (the term "zymogen" referring to the inactive precursor enzymes). Trypsinogen is an inactivated forms of trypsin, and chymotrypsinogen is an inactivated form of chymotrypsin.
Once released in the intestine, the enzyme enteropeptidase (formerly, and incorrectly, called 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.

Regulation

The pancreas receives regulatory innervation via hormones in the blood and through the autonomic nervous system. These two inputs regulate the secretory activity of the pancreas.

Sympathetic (adrenergic)	Parasympathetic (muscarinic)
α2: decreases secretion from beta cells, increases secretion from alpha cells	M3[6] increases stimulation of alpha cells and beta cells

Diseases

Because the pancreas is a storage depot for digestive enzymes, injury to the pancreas is potentially very dangerous. A puncture of the pancreas generally requires prompt and experienced medical intervention.

Pancreatic cancers, particularly cancer of the exocrine pancreas, remain one of the most deadly cancers, and the mortality rate is very high.

Diabetes mellitus type 1 is a chronic autoimmune disorder in which the immune system attacks the insulin-secreting cells in the pancreas

SUBMITTED TO :                                                    SUBMITTED BY :

Dr V ASHOK                                                              RV/07-63

ASST PROFESSOR                                                    RV/07-62

DEPT OF VBC                                                            RV/07-65