Insulin is a hormone that regulates the body’s use of sugars and other nutrients. It is produced in specialized cells in the islets of Langerhans, a part of the pancreas. Insulin also affects the body’s use of protein, fat, and mineral products, such as potassium and phosphate.
How insulin acts in the body.
When food is absorbed into the bloodstream, the pancreas increases the secretion of insulin into the blood. Insulin speeds the movement of nutrients from the bloodstream into target cells mainly in liver, muscle, and fat tissues. Specialized protein molecules called insulin receptors lie on the surface of the target cells. The insulin receptors bind to insulin, activating the receptors. The activated receptors signal the cell to hasten the transport of nutrients across the cell membrane and increase the activity of enzymes within the cell to utilize the nutrients. Glucose and other simple sugars, produced by the digestion of carbohydrates, are used for immediate energy or converted to glycogen for storage. Amino acids, produced by the digestion of proteins, are transported into cells, where they form the building blocks for proteins. Fatty acids, produced by the digestion of fats, are converted to triglycerides for storage and later used for energy.
Diabetes.
A complete lack of insulin in the body results in a severe illness called Type 1 diabetes mellitus. This is caused by destruction of the insulin-producing cells in the pancreas by the body’s own immune system. A milder form of diabetes, called Type 2 diabetes, occurs when the pancreas is unable to produce a sufficient quantity of insulin. In addition, the body is unable to utilize insulin properly, a condition called insulin resistance. The cause of Type 2 diabetes is not known, but genetic and environmental factors play a role. Some people suffer from producing too much insulin, causing the blood sugar level to fall below normal, a condition called hypoglycemia. See Hypoglycemia.
In treating diabetes, insulin is usually injected under the skin. If insulin is taken by mouth, digestive fluids destroy the hormone. Treatment with insulin does not cure diabetes, but it does control the disease and allow the patient to live an almost normal life. Until the early 1980’s, insulin for diabetics was obtained chiefly from the pancreases of cattle and hogs. Today, insulin is also produced by genetically engineered bacteria (see Genetic engineering (Uses of genetic engineering)).
Pure insulin is rapidly absorbed by the body and its effect lasts only a short time. Drug companies manufacture various insulin preparations that prolong the hormone’s effect. Such preparations are made by combining insulin with proteins or by modifying the hormone’s chemical structure. To best mimic the body’s normal pattern of insulin secretion, diabetic patients may use different types of insulins and administer them one to five times daily. Some diabetics have insulin pumps implanted under the skin. The pumps are programmed to release insulin at specific times. Scientists have also developed a form of insulin that can be taken by inhalation.
History.
The existence of a sugar-regulating substance in the pancreas was shown by surgical experiments on dogs in 1889 in Germany by two physicians, Oscar Minkowski and Joseph von Mering. Researchers at the University of Toronto, particularly Frederick G. Banting, Charles H. Best, John J. R. Macleod, and James B. Collip, isolated and prepared insulin. They used it for the first time in diabetic patients in 1922. The first genetically engineered human insulin was produced by American scientists in 1978.
