insulin

Protein hormone, produced by specialized cells in the islets of Langerhans in the pancreas, which regulates the metabolism (rate of activity) of glucose, fats, and proteins. In this way it helps to regulate the concentration of glucose in the blood of mammals. If the blood glucose concentration is too high, the pancreas releases insulin into the blood. This causes blood glucose levels to fall. This is partly due to increased uptake of glucose into most body cells (except liver and brain) but also because the liver converts glucose into insoluble glycogen and stores it instead of making glucose. In diabetes, a person's blood glucose may rise to such a high concentration that it can kill. This may be because the pancreas does not make enough insulin, or because the body cells respond less to the insulin.

Normally, insulin is secreted in response to rising blood sugar levels (after a meal, for example), stimulating the body's cells to store the excess. Failure of this regulatory mechanism in diabetes mellitus requires treatment with insulin injections or capsules taken by mouth. Types vary, from pig and beef insulins to synthetic and bioengineered ones. They may be combined with other substances to make them longer- or shorter-acting. Implanted, battery-powered insulin pumps deliver the hormone at a preset rate, to eliminate the unnatural rises and falls that result from conventional, subcutaneous (under the skin) delivery.

Insulin was discovered by Canadian physician Frederick Banting and Canadian physiologist Charles Best, who pioneered its use in treating diabetes.