What is Insulin

“Injections of insulin are necessary for those living with Type 1 Diabetes because it cannot be treated by diet and exercise alone.”

Insulin is a principal hormone produced by our pancreas which makes our body’s cells absorb glucose from the blood. It regulates of the uptake of glucose from the blood into most cells of the body, especially liver, muscle, and adipose tissue and stops the body from using fat as a source of energy. Therefore deficiency of insulin or the insensitivity of its receptors plays a central role in all forms of Diabetes Mellitus.

The body obtains glucose from three main places:

  • the intestinal absorption of food,
  • the breakdown of glycogen, the storage form of glucose found in the liver,
  • and gluconeogenesis, the generation of glucose from non-carbohydrate substrates in the body.

Insulin plays a critical role in balancing glucose levels in the body. Insulin can inhibit the breakdown of glycogen or the process of gluconeogenesis, it can stimulate the transport of glucose into fat and muscle cells, and it can stimulate the storage of glucose in the form of glycogen. Also without insulin the body uses fat as a source of energy.

Insulin is released into the blood by beta cells (β-cells), found in the islets of Langerhans in the pancreas, in response to rising levels of blood glucose, typically after eating. Insulin is used by about two-thirds of the body’s cells to absorb glucose from the blood for use as fuel, for conversion to other needed molecules, or for storage. Lower glucose levels result in decreased insulin release from the beta cells and in the breakdown of glycogen to glucose. This process is mainly controlled by the hormone glucagon, which acts in the opposite manner to insulin.

Effect of insulin on glucose uptake and metabolism
Effect of insulin on glucose uptake and metabolism / Photo credit: WikiPedia

If the amount of insulin available is insufficient, if cells respond poorly to the effects of insulin (insulin insensitivity or insulin resistance), or if the insulin itself is defective, then glucose will not be absorbed properly by the body cells that require it, and it will not be stored appropriately in the liver and muscles. The net effect is persistently high levels of blood glucose, poor protein synthesis, and other metabolic derangements, such as acidosis.

When the glucose concentration in the blood remains high over time, the kidneys will reach a threshold of reabsorption, and glucose will be excreted in the urine (glycosuria). This increases the osmotic pressure of the urine and inhibits reabsorption of water by the kidney, resulting in increased urine production (polyuria) and increased fluid loss. Lost blood volume will be replaced osmotically from water held in body cells and other body compartments, causing dehydration and increased thirst (polydipsia).

There are four main types of insulin:

  • rapid acting insulin: is used as a bolus dosage. The action onsets in 15 minutes with peak actions in 30 to 90 minutes.
  • short acting insulin: action onsets within 30 minutes with the peak action around 2 to 4 hours.
  • intermediate acting insulin: action onsets within 1 to 2 hours with peak action of 4 to 10 hours.
  • long acting insulin: is usually given once per day.

In addition to insulin therapy dietary management is important. Injections of insulin either via subcutaneous injection or insulin pump are necessary for those living with Type 1 Diabetes because it cannot be treated by diet and exercise alone.

Although insulin is not identical in all the animal, humans can receive animal insulin. The porcine insulin, which is insulin from a pig is the most similar to human insulin and genetic engineering has allowed us to synthetically produce “human” insulin.

Today, the most common insulins are biosynthetic products produced using genetic recombination techniques; formerly, cattle or pig insulins were used, and even sometimes insulin from fish.

Researched, collected and written by Zsolt Szemerszky

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