Insulin is the internal secretion of the pancreas formed by groups of cells called the islets of Langerhans. It is the hormone needed to enable glucose to enter the cells and provide energy. Insulin is also important in keeping blood glucose levels within the acceptable limits.
Insulin is injected into the body by people with type 1 diabetes in whom the cells that produce insulin have been destroyed. This is the most common form of diabetes in children and young adults, and they depend on insulin for survival. Insulin may also be used by people with type 2 diabetes. In type 2 diabetes, the body needs more insulin than it can produce.
Since the landmark discovery of insulin by Frederick Banting and Charles Best in 1921, huge steps have been taken in research and development in creating genetically engineered human insulin. Insulin was previously derived only from the pancreas of cattle and pigs.