Islets of Langerhans is the area in which the endocrine cells of the pancreas are grouped. They constitute approximately 1 to 2% of the mass of the pancreas. There are about one million islets in a healthy adult human pancreas, which are distributed evenly throughout the organ. The islets of Langerhans are clusters of specialized cells that produce insulin and glucagon. Named after the German pathologist Paul Langerhans (1847-1888), who discovered them in 1869, these cells sit in groups that Langerhans likened to little islands in the pancreas.
The islets of Langerhans make up the endocrine pancreas and consist of five different types of cells which secret hormones directly into the bloodstream; α (alpha), β (beta), δ (delta), PP, and ε (epsilon) cells. α cells produce glucagon; β insulin; δ somatostatin; PP polypeptide; and ε ghrelin. Glucagon raises the level of sugar (glucose) in the blood, whereas insulin lowers the level of glucose.