Glucagon

Glucagon is an hormone secreted by the endocrine pancreas. Along with insulin it is involved in carbohydrate metabolism. Glucagon is released when the glucose level in the blood is low, which is called hypoglycemia, causing the liver to convert stored glycogen into glucose and release it into the bloodstream. The action of glucagon is thus opposite to that of insulin, which instructs the body's cells to take in glucose from the blood in times of satiation.

Glucagon is a 29-amino acid polypeptide, which is synthesized and secreted from α (alpha) cells of the islets of Langerhans in the endocrine pancreas. The amino acid sequence of glucagon was described in the late-1950s. A more complete understanding of its role in physiology and disease was not established until the 1970s, when a specific radioimmunoassay was developed.