Islet of Langerhans. Light micrograph of a section through an islet of Langerhans in a pancreas. Scattered throughout the pancreas, the islets are endocrine cells that secrete a range of hormones, most notably insulin and glucagon, which are essential for normal body homeostasis. Each islet is supplied by capillaries (tiny blood vessels) passing through it and surrounded by pancreatic acinar cells that synthesise and secrete numerous enzymes involved with digestive functions in the small bowel. Islet cells arise from common precursor stem cells in the embryonic/foetal pancreas. A failure by islet cells to produce insulin is classed as type 1 or insulin-dependent diabetes, and often is a result of autoimmune destruction of the islet cells. Magnification: