Special groups of cells in the pancreas. They make and secrete hormones that help the body break down and use food. Named after Paul Langerhans, the German scientist who discovered them in 1869, these cells sit in clusters in the pancreas. There are five types of cells in an islet: beta cells, which make insulin; alpha cells, which make glucagon; delta cells, which make somatostatin; and PP cells and D1 cells, about which little is known.