Pancreatic secretion exocrine cell

The trypsin family of proteases plays a role in acute and chronic pancreatitis, as well as leads to its ultimate destruction [4, 105]. In pancreatitis, active exocrine enzymes are prematurely released inside the pancreatic duct. Various factors can contribute to the development of acute pancreatitis. Trypsinogen, chymotrypsinogen, procarboxypeptidase, and proelastase are inactive proforms of proteolytic enzymes produced by the pancreatic acinar cells. Following secretion these enzymes are activated in a cascade that converts trypsinogen to trypsin in the duodenum and/or small intestine. 

The pancreas contains endocrine cells, which secrete hormones directly into the bloodstream, and exocrine cells, which secrete zymogen precursors of digestive enzymes into the upper small intestine. The endocrine tissue contains cell clusters known as islets of Langerhans, which contain at least four different cell types (A, D, P, and B), each specialized for synthesis of one hormone. The A cells produce glucagon the D cells, somatostatin and the P cells, a recently discovered pancreatic hormone. Insulin is synthesized in the B cells, which sense glucose levels and secrete insulin in response to increased levels of blood glucose. 

Although it is possible to list all of the mammalian secretory cells and to note in some detail the biochemical nature of both precursor material and final secretory product, as well as to describe the intracellular pathway of secretory product formation, this would defeat the purpose of the current discourse. Rather, it will be more instructive to examine one secretory cell in detail and to compare it to several other representative cell types. From this analysis, one may derive an overview of the general mechanisms of secretion. For this purpose, I have chosen as a starting point the pancreatic exocrine cell because this cell has been one of the most thoroughly investigated, and its secretory pattern provides an ideal model on which to build broad concepts. 

The pancreas possesses both endocrine and exocrine fnnctions. The islets of Langerhans, which contain the cells of the endocrine pancreas, secrete insnlin, glncagon, somatostatin, and other polypeptide hormones. The exocrine pancreas is composed of acini that secrete about 1 to 2 L/day of isotonic fluid that contains water, electrolytes, and pancreatic enzymes necessary for digestion. Bicarbonate is secreted primarily by the centroacinar (ductular) cells, and is the principal ion of physiologic importance. Pancreatic juice is delivered to the duodenum via the pancreatic ducts (Fig. 39-1) where the alkaline secretion (pH about 8.3) neutralizes gastric acid and provides an appropriate pH for maintaining the activity of pancreatic enzymes."... 

Pancreas A major endocrine and exocrine organ located behind the stomach. It secretes pancreatic juice into the duodenum to neutrahze the effluent from the stomach and supply digestive enzymes. It also synthesizes and secretes the hormones insulin, glucagon, and somatostatin into the bloodstream from cells within the islets of Langerhans. 

Beaudoin, A. R. Mercier, M. (1982). Exocytosis in mammalian cells. VI. Temperature dependence of pancreatic exocrine secretion. Can. J. Physiol. Pharmacol. 58, 1509-1512. 

PP occurs in endocrine cells in the pancreatic islets (Alumets et al., 1978), and the peptide inhibits pancreatic exocrine secretion and gall bladder contraction (Schwartz,... 

The vertebrate NPY family contains such prominent members as pancreatic polypeptide (PP), characterized initially from chicken where PP is synthesized and released from the endocrine cells of the pancreatic islets [204], neuropeptide Y (NPY) found in porcine brain [205] and peptide YY (PYY) isolated from porcine intestine [206]. Such peptides are characterized by a chain length of 36 amino acids and Tyr-amide at the C-terminus. Whereas NPY is exclusively expressed in neurons of mammals and is known to control processes such as stimulation of food intake, vasoconstriction, sexual behaviour and circadian rhythm, PP and PPY are synthesized in endocrine cells of the gut and are inhibitors of gut motility and of the secretion of exocrine products from the pancreas. 

Insulin and glncagon are synthesized in different cell types of the endocrine pancreas, which consists of microscopic clnsters of small glands, the islets of Langerhans, scattered among the cells of the exocrine pancreas. The a cells secrete glncagon, and the 3 cells secrete insnlin into the hepatic portal vein via the pancreatic veins. 

Peptide YY (PYY) Enteroendocrine cells, developing pancreas alpha cells in mature islets 1. Inhibits both gastric acid secretion and gastric motility 2. Slows intestinal motility 3. Inhibits pancreatic exocrine secretion 1. Oral nutrient ingestion 2. Bile acids and fatty acids 3. Amino acids in colon... 

In vitro, the capillary endothelial cells of the pancreas are still attached to the outer rim of whole islets postisolation and, with conditioned medium, may be coaxed to proliferate outward onto extracellular matrix-coated plastic plates for further mechanistic studies and functional analyses. The isolated capillary endothelial cells can be characterized by examining a-1 proteinase inhibitor and nephrin expression via immunocytochemistry or flow cytometry (Zanone et al., 2008). Not only do these endothelial cells play a role in drug candidate-induced effects on insulin secretion and glucose regulation of islets, but they also act as the regulators of leukocyte recruitment into the islets. The pancreatic microvasculature is therefore likely to play a role in the altered physiology of the endocrine and exocrine pancreas if affected by drug candidate exposure. 

Chymotrypsin, trypsinogen, and procarboxypeptidase are excretory secretion products of two organs combined into one anatomical structure the endocrine pancreas, which elaborates insulin, and the exocrine pancreas, which secretes the pancreatic juice. Histologically, the exocrine pancreas resembles the salivary glands. The unique feature of the exocrine pancreatic cell is the zymogen granules, the formation and secretion of which are discussed in another section of this book. 

After the histological studies of Laguesse revealed the distinction between two major secretory systems in the pancreas—namely, the islets and the exocrine pancreas. Banting and Best demonstrated that insulin is secreted by the islet cell. The critical experiment was the ligation of the pancreatic duct, which destroys the exocrine pancreas but leaves the endocrine pancreas intact. Banting and Best showed that such a procedure does not induce diabetes. 

Several lines of evidence show that insulin is elaborated in the jS cells of the pancreas. First of all, the islets, rather than the exocrine pancreas, clearly are involved in insulin secretion because pancreatic duct ligation leads to atrophy of the exocrine gland without inducing diabetes. 

The pancreas is a gland that lies in the duodenal loop and has two secretory functions the endocrine process for the production of insulin and the exocrine process for the production of digestive enzymes (from the acinar cells), water and electrolytes (from the duct cells), which together form the pancreatic juice, which is secreted into the duodenum through the pancreatic duct. The proportions of the different enzymes change in response to the nature of the diet. 

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