Islets of Langerhans
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The endocrine (i.e., hormone-producing) cells of the pancreas are grouped in the islets of Langerhans. Discovered in 1869 by the German pathological anatomist Paul Langerhans, the islets of Langerhans 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 interspersed evenly throughout the organ, and their combined weight is 1 to 1.5 grams. Each islet contains approximately one thousand cells and is 50-500 μm in diameter.
Hormones produced in the Islets of Langerhans are secreted directly into the blood flow by (at least) four different types of cells:
- Insulin-producing Beta cells (65-80% of the islet cells)
- Glucagon-releasing alpha cells (15-20%)
- Somatostatin-producing delta cells (3-10%)
- Pancreatic polypeptide-containing PP cells (1%)
Islets can influence each other through paracrine and autocrine communication, and beta-cells are coupled electrically to beta-cells (but not to other cell-types).
The paracrine feedback system of the islets of Langerhans has the following structure:
- Insulin: Activates beta cells and inhibits alpha cells.
- Glucagon: Activates beta cells and delta cells.
- Somatostatin: Inhibits alpha cells and beta cells.
Electrical activity of pancreatic islets has been studied using patch clamp techniques, and it has turned out that the behaviour of cells in intact islets differs significantly from the behaviour of dispersed cells.
| Endocrine system - Pancreas - edit |
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| Islets of Langerhans: alpha cell | beta cell | delta cell | PP cell |
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