The hormone produced by the pancreas that raises blood sugar is glucagon.
Glucagon is a peptide hormone made mainly by alpha cells in the islets of Langerhans, clusters of endocrine cells scattered throughout the pancreas. When blood glucose falls, alpha cells release glucagon into the bloodstream. Its principal target is the liver, where it helps restore circulating glucose by stimulating glycogenolysis—the breakdown of stored glycogen—and gluconeogenesis, the production of new glucose.
Glucagon works in opposition to insulin, which is made by pancreatic beta cells and generally lowers blood glucose by promoting uptake and storage. This does not make glucagon an “opposite version” of insulin in every biological detail; the two hormones coordinate constantly to keep glucose within a useful range, especially between meals, during fasting, or during exercise.
The hormone was discovered in the early 1920s by John Murlin and Charles Kimball while studying pancreatic extracts. In medicine, injectable glucagon can treat severe hypoglycemia when a person cannot safely swallow sugar. It is also used in some diagnostic procedures because it can temporarily relax parts of the digestive tract.