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Insulin is a hormone secreted by the cells of the pancreas. It is produced by the beta cells of the islets of Langerhans. The cells of the pancreas that are responsible for producing insulin were discovered by Paul Langerhans, a German pathologist and biologist. These cells look like islands, for which they were named as the islets of Langerhans.

In the islets of Langerhans, two types of cells are found - alpha and beta cells. The beta cells are associated with the production and the secretion of insulin. The term insulin is derived from the Latin word insula, which means islands. Its main function is to regulate the blood glucose level.

Understanding the Functions of Insulin

This hormone ensures the absorption of glucose by the cells of the muscle, liver, and the fat tissues from the bloodstream. It also helps the liver and the muscle cells store glucose in the form of glycogen for future use. Insulin prevents the use of fats for deriving energy.

It is released in the body in two phases. In the first phase, a large amount of insulin is released in response to an increase in the level blood glucose following the digestion of food. A high level of insulin in the body induces the cells of the liver and muscles to absorb glucose from the bloodstream. This results in a reduction in the level of blood glucose.

With a reduction in the level of blood glucose, the secretion of insulin decreases. In the second phase, a small amount of insulin is continuously secreted by the beta cells irrespective of the level of glucose in blood. The body needs this small amount of insulin, as the liver continues to release the stored glucose into the bloodstream even when we are not eating. This ensures a constant supply of energy.

Insulin enters the blood plasma and binds with the beta globulins (a protein). Globulins are of two types - alpha and beta globulins, and they are concerned with the circulation of lipids, vitamins, and hormones. When blood plasma comes in contact with the liver and muscle cells, the insulin bound to the beta globulins interacts with the receptors embedded in the plasma membrane or cytoplasm of the cells. This facilitates the passage of glucose into the cells.

In the absence of enough insulin, the absorption of glucose gets impaired. As a result, the body tends to use the stored fats to derive energy. But in the process, harmful byproducts like ketones are generated. On the other hand, the blood glucose level increases, as the body fails to absorb and utilize glucose in the absence insulin.

Besides regulating the level of blood glucose, this hormone affects many metabolic activities within the body. It stimulates certain enzymes that can increase the rate of glycogenesis or the conversion of glucose into glycogen in the liver and muscle cells. In addition to these, a high level of insulin stimulates the production of fats from glucose, and prevents gluconeogenesis or the generation of glucose from non-carbohydrate carbon substrates like lactate, pyruvate, and glycerol. It also plays an important role in the synthesis of DNA and RNA, and cell replication. It can also raise the transportation of amino acids to the cells.