False-colour scanning electron micrograph of the surface of a single islet of Langerhans from a mammalian pancreas. About one million islets are scattered throughout the pancreas. Some 3,000 cells in each islet secrete a variety of hormones. The most numerous are the insulin-producing (beta) cells which secrete insulin directly into the bloodstream. Insulin's main role is in controlling the transport of glucose; insulin deficiency results in diabetes. Other hormones secreted by different cells in the islet include glucagon, pancreatic polypeptide, and somatostatin. Magnification: x233 at 35mm size.