Insulin is a protein hormone produced by the beta cells of the pancreas. Insulin is an anabolic hormone that stimulates the uptake of glucose into fat and muscle and promotes the formation of glycogen.

Insulin stimulates protein synthesis and inhibits protein degradation. Glucose, amino acids, and certain pancreatic and gastrointestinal hormones (eg, glucagon, gastrin, secretin) stimulate the pancreas to secrete insulin. Insulin secretion is inhibited by hypoglycemia and somatostatin.

In healthy individuals insulin is secreted in a pulsatile fashion that is closely controlled by glucose levels. Insulin levels can be useful predicting susceptibility to the development of type II diabetes, although C-peptide has largely supplanted insulin measurement for this role.