Principles of Biochemistry, Volume 3 - A. Lehninger 1985

Selected Aspects of Human Biochemistry
Hormones
The pancreas secretes a number of hormones that regulate metabolic processes

Let us consider another pathway for the REGULATION OF CARBOHYDRATE METABOLISM, as well as that of Amino Acids and Lipids, namely, regulation by Hormones secreted by the Pancreas, whose endocrine activity is in turn regulated by Hormones of the anterior Pituitary Gland.

The pancreas performs two primary biochemical Functions. One is The Biosynthesis of A number of Enzymes, notably Trypsin, Chymotrypsin, and carboxypeptidase, which are secreted into the intestine and participate in food Digestion. This function is carried out by exocrine Cells (“secreting outward,” i.e., into the pancreatic duct) (Fig. 25-15). Another important function of the pancreas is the biosynthesis of Insulin and several other polypeptide hormones that regulate the metabolism of glucose and other major nutrients. This function is performed by the endocrine tissue of the pancreas, which consists of clusters of specialized cells called the islets of Langerhans. The islets contain several closely related Cell types, with each cell type producing a single pancreatic hormone (Fig. 25-15 and Table 25-5). The islets of Langerhans secrete the following hormones: Glucagon, produced by A cells; insulin, produced by B cells; Somatostatin, produced by D cells; and Pancreatic Polypeptide (a relatively recently discovered hormone that lacks a universally accepted name as yet), produced by F cells. Although all of these hormones play individual roles of importance in metabolism, particularly Carbohydrate Metabolism, insulin holds the primary position in significance. Despite the exceptional importance of insulin in the Treatment of Diabetes Mellitus, we still do not know precisely how this hormone exerts its vital physiological effect. Investigating The Mechanism of insulin action remains one of the most intensively researched problems in modern Biochemistry and Medicine.

Class="center">Table 25-5. Pancreatic Hormones