glucagon

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glucagon

(glo͞o`kəgŏn), hormonehormone,
secretory substance carried from one gland or organ of the body via the bloodstream to more or less specific tissues, where it exerts some influence upon the metabolism of the target tissue.
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 secreted by the α cells of the islets of Langerhans, specific groups of cells in the pancreaspancreas
, glandular organ that secretes digestive enzymes and hormones. In humans, the pancreas is a yellowish organ about 7 in. (17.8 cm) long and 1.5 in. (3.8 cm) wide. It lies beneath the stomach and is connected to the small intestine at the duodenum (see digestive system).
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. It tends to counteract the action of insulininsulin,
hormone secreted by the β cells of the islets of Langerhans, specific groups of cells in the pancreas. Insufficiency of insulin in the body results in diabetes. Insulin was one of the first products to be manufactured using genetic engineering.
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, i.e., it raises the concentration of glucose in the blood. Glucagon was first purified and crystallized in 1955; the amino acid sequence of this 29-amino acid polypeptide (see peptidepeptide,
organic compound composed of amino acids linked together chemically by peptide bonds. The peptide bond always involves a single covalent link between the α-carboxyl (oxygen-bearing carbon) of one amino acid and the amino nitrogen of a second amino acid.
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) was published in 1956–57. One of the most important actions of glucagon is the promotion of glycogenolysis, i.e., the degradation of glycogenglycogen
, starchlike polysaccharide (see carbohydrate) that is found in the liver and muscles of humans and the higher animals and in the cells of the lower animals. Chemically it is a highly branched condensation polymer of glucose; it is readily hydrolyzed to glucose.
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 to glucose, in the liver. Glucagon stimulates adenyl cyclase, the enzyme that catalyzes the conversion of adenosine triphosphateadenosine triphosphate
(ATP) , organic compound composed of adenine, the sugar ribose, and three phosphate groups. ATP serves as the major energy source within the cell to drive a number of biological processes such as photosynthesis, muscle contraction, and the synthesis of
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 to 3′5′-cyclic adenosine monophosphateadenosine monophosphate
(AMP) , organic compound composed of an adenine base, the sugar ribose, and one phosphate unit. AMP is one of the possible products of the hydrolysis of adenosine triphosphate (ATP) and is therefore important in the transfer of chemical energy during
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 (cyclic AMP).

Glucagon

The protein hormone secreted by the pancreas which is known to influence a wide variety of metabolic reactions. Glucagon, along with insulin and other hormones, plays a role in the complex and dynamic process of maintaining adequate supplies of sugar in the blood. Glucagon has often been called the hyperglycemic-glycogenolytic factor because it causes the breakdown of liver glycogen to sugar (a process known as glycogenolysis) and thereby increases the concentration of sugar in the bloodstream (a condition known as hyperglycemia). Glucagon may also be involved in the regulation of protein and fat metabolism, gastric acid secretion and gut motility, excretion of electrolytes (such as sodium, potassium and chloride) by the kidney, contractility of heart muscle, and release of insulin from the pancreas. Glucagon is used in human medicine chiefly in certain diabetic conditions when a dangerously low blood sugar must be rapidly raised. See Carbohydrate metabolism, Glycogen, Hormone, Insulin, Pancreas

glucagon

[′glü·kə‚gän]
(biochemistry)
The protein hormone secreted by α-cells of the pancreas which plays a role in carbohydrate metabolism. Also known as hyperglycemic factor; hyperglycemic glycogenolytic factor.