Endocrine Pancreas Functions, Tissue & Cells Types

Presentation Notes on pancreatic endocrine cell development, Classifications, Roles in Diabetes, Hormones & Disease  for medical & biology students in ppt / .doc / word Format

NORMAL ENDOCRINE PANCREAS :

The endocrine pancreas consists of about 1million microscopic clusters of cells, the islets of Langerhans. The first evidence of islet formation in the human fetus is seen at 9 to 11 weeks. Embryologically, both endocrine and exocrine components of the pancreas are endodermal derivatives. Several transcription factors have now been identified that determine lineage specification (i.e., endocrine versus exocrine) in the developing pancreas. For example, expression of the transcription factor neurogenin 3 (Ngn3) delinates endocrine progenitors that eventually give rise to mature islet cells.

In aggregate, the islets in the adult human weigh only 1 to 1.5 gm, individually, most islets measure 100 to 200 mm and consists of four major and two minor cell types. The four major types are b, a, d and PP (pancreatic polypeptide) cells and the two minor types are D1 and enterochromaffin cells. The major types make up about 68%, 20%, 10% and 2% respectively, of the adult islet cell population. They can be differentiated morphologically by their staining properties, by the ultra structural characteristics of their granules, and by their hormone content.

The b cell produces insulin, as will be detailed in the discussion of diabetes. The insulin  containing intracellular granules contain a crystalline matrix with a rectangular profile, surrounded by a halo. The a cell produces Glucagon and the granules are found with closely applied membranes and dense center. d cells contain Somatostatin, which suppresses both insulin and glucagon release . They have large, pale granules with closely applied membranes. PP cells contain a unique pancreatic polypeptide that exerts a number of gastrointestinal effects, such as stimulation of secretion of gastric and intestinal enzymes and inhibition of intestinal motility. These cells have small, dark granules and not only are present in islets, but also are scattered in the exocrine pancreas.

The minor cell type D1 cell elaborate vasoactive intestinal polypeptide (VIP), a hormone that induces glycogenolysis and hyperglycemia ; it also stimulates gastrointestinal fluid secretion and causes secretory diarrhoea and Enterochromaffin cells synthesize serotonin and are the source of pancreatic tumors that causes the carcinoid syndrome. 

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