Glucagon
Glucagon is a a 29 amino acid polypeptide acting as an important hormone in carbohydrate metabolism. The polypeptide has a molecular weight of 3485 daltons and was discovered in 1923 by Kimball and Murlin. They studied panreatic extracts and found a additional substance with hyperglycemic properties. Glucagon was sequenced in late 1950s. Fuller understanding of its role in physiology and disease was established in 1970s when a specific radioimmunoassay was developed.
NH2-His-Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser-Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu-Met-Asn-Thr-COOH
Physiology
The hormone is synthesized and secreted from alpha cells of pancreatic islets (Islets of Langerhans).
Glucagon maintains the level of glucose in the blood by binding to specific receptors on hepatocytes causing the liver to release its intracellular stores of glucose. As these stores (in the form of glycogen) become depleted, glucagon then encourages the liver to synthesize glucose by gluconeogenesis. This glucose is released into the bloodstream. Both theses mechanisms leading to glucose release by liver prevent the development of hypoglycaemia.
Pathology
Pharmacological application of glucagon
An injectable form of glucagon is essential first aid in cases of
severe hypoglycemia. The glucagon is injected and quickly raises blood glucose levels. It works only if there is glycogen stored in liver cells, and it won't work again until those stores are replenished.
Glucagon has also inotropic properties. Although its use is impracticable in heart failure, it has some value in treatmeant of myocardium depression secondary to betablocker overdose.
See also
Referenced By
Delta cell | Diabetes dictionary | Islet of Langerhans | Islets of Langerhans | List of human blood components
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