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What is Insulin?

Updated on April 13, 2012

Insulin is a hormone that is essential for the proper use and storage of ingested sugar in the body. The hormone is secreted by certain cells of the islets of Langerhans in the pancreas.

It is secreted at a high rate when sugar is absorbed from the gastrointestinal tract and at a low rate during fasting.

Insulin acts to speed the passage of sugar in the forn1 of glucose (a simple sugar that is the primary source of energy in the body) across cell membranes to the cell's metabolic machinery, where the glucose is oxidized and used as a source of energy by the body. Insulin also promotes the conversion of excess glucose into a storage form of sugar, known as glycogen, in the liver. As the level of glucose in the blood falls, insulin secretion stops and glycogen in the liver is broken down and released into the bloodstream as glucose. Thus, insulin, acting in concert with the liver, maintains a relatively constant level of glucose in the bloodstream. Insulin also promotes the conversion of glucose into fat. During fasting, this fat is used as a metabolic fuel by the body.

The administration or secretion of a large amount of insulin (hyperinsulinism) causes hypoglycemia, a condition in which there is an abnormally low concentration of glucose in the blood. Since the nervous system is heavily dependent on glucose as a metabolic fuel, a decreased level of glucose causes tremor, sweating, anxiety, confusion, and even coma. Diabetes mellitus in man and experimental animals is the result of a deficiency of insulin.

It is characterized by an abnormally high concentration of glucose in the blood (hyperglycemia) and by the excretion of sugar in the urine (glucosuria). This condition exists when insulin secretion is below normal or when other substances in the body inhibit the action of insulin. Insulin was first extracted from the pancreas by two Canadian scientists, Charles H. Best and Frederick G. Banting, in 1921.

It was later isolated in pure crystalline form and found to be a protein composed of 51 amino acids. Insulin is now prepared from the pancreatic tissues of domestic animals for use in the treatment of diabetes mellitus.

Insulin was first synthesized in mainland China in 1966.


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