Islets of Langerhans
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A porcine islet of Langerhans. The left image is a brightfield image created using hematoxylin stain; nuclei are dark circles and the acinar pancreatic tissue is darker than the islet tissue. The right image is the same section stained by immunofluorescence against insulin, indicating beta cells. |
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.
Since the islets of langerhans are destroyed in type I diabetes, clinicians and researchers are actively pursuing islet transplantation technology as a means of curing this disease.
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