insulin

/in"seuh lin, ins"yeuh-/, n.

1. Biochem. a polypeptide hormone, produced by the beta cells of the islets of Langerhans of the pancreas, that regulates the metabolism of glucose and other nutrients.

2. Pharm. any of several commercial preparations of this substance, each of which allows a particular rate of absorption into the system: genetically engineered or obtained from the pig or ox pancreas, and used in the treatment of diabetes to restore the normal ability of the body to utilize sugars and other carbohydrates.

[1910-15; INSUL(A) + -IN²]

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Polypeptide hormone (see peptide) that regulates blood glucose levels.

Secreted by the islets of Langerhans (see Langerhans, islets of) in the pancreas when blood glucose rises, as after a meal, it helps transfer the glucose into the body's cells to be oxidized (see oxidation-reduction) for energy or converted and stored as fatty acids or glycogen. When blood glucose falls, insulin secretion stops and the liver releases more glucose into the blood. Insulin has various related functions in the liver, muscles, and other tissues, controlling the balance of glucose with related compounds. Insulin-related disorders include diabetes mellitus and hypoglycemia. Frederick Banting and J.J.R. Macleod won a Nobel Prize in 1923 for discovering insulin, and Frederick Sanger won one in 1958 for determining its amino acid sequence.

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      hormone that regulates the level of sugar ( glucose) in the blood and is produced by the beta cells of the islets of Langerhans (Langerhans, islets of) in the pancreas. Insulin is secreted when the level of blood glucose rises—as after a meal. When the level of blood glucose falls, secretion of insulin stops, and the liver releases glucose into the blood.

      Insulin is a simple protein in which two polypeptide chains of amino acids are joined by disulfide linkages. Insulin helps transfer glucose into cells so that they can oxidize the glucose to produce energy for the body. In adipose (fat) tissue, insulin facilitates the storage of glucose and its conversion to fatty acids. Insulin also slows the breakdown of fatty acids. In muscle it promotes the uptake of amino acids for making proteins. In the liver it helps convert glucose into glycogen (the storage carbohydrate of animals) and it decreases gluconeogenesis (the formation of glucose from noncarbohydrate sources). The action of insulin is opposed by glucagon, another pancreatic hormone, and by epinephrine.

      Inadequate production of insulin is responsible for the condition called diabetes mellitus. Severe diabetics require periodic injections of insulin, which is extracted from the pancreas of pigs, sheep, and oxen. Insulin was first isolated as a pancreatic extract in 1921 by the Canadian scientists Sir Frederick G. Banting (Banting, Sir Frederick Grant) and Charles H. Best (Best, Charles H.). By the early 1980s certain strains of bacteria had been genetically modified to produce human insulin.

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