CAROL AND MIKE WERNER / SCIENCE PHOTO LIBRARY CAROL AND MIKE WERNER / SCIENCE PHOTO LIBRARY
The islets of Langerhans are groups of specialized cells in the pancreas that make and secrete hormones. There are five types of cells in an islet: alpha cells (blue) that make glucagon, which raises the level of glucose (sugar) in the blood; beta cells (yellow -- shown in cross-section) that make insulin; delta cells (purple) that make somatostatin which inhibits the release of numerous other hormones in the body; and PP cells and D1 cells, about which little is known. Insulin molecules are shown as green spheres; glaucagon molecules as blue spheres and glucose molecules as grey spheres. Insulin and glucagon can be seen entering the blood stream through the walls of capillaries. Degeneration of the insulin-producing beta cells is the main cause of type I (insulin-dependent) diabetes mellitus.
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