in·su·lin (ĭnˈsə-lĭn)

1. A polypeptide hormone that is secreted by the islets of Langerhans, helps regulate the metabolism of carbohydrates and fats, especially the conversion of glucose to glycogen, and promotes protein synthesis and the formation and storage of neutral lipids.
2. Any of various pharmaceutical preparations containing this hormone that are derived from the pancreas of certain animals or produced through genetic engineering and are used parenterally in the medical treatment and management of insulin-dependent diabetes mellitus.