Langerhans Islands
The islets of Langerhans (also called islets of Langerhans , pancreatic islands or islet cells (not to be confused with the Langerhans cells ) and in their entirety often referred to as the islet organ ) are island-like, embedded collections of hormone-forming cells in the pancreas that both increase the height of the Register blood sugar as well as produce and release insulin . They were discovered in 1869 by the budding physician Paul Langerhans as a "rounded heap" in the endocrine tissue of the pancreas, described and later named after him. They belong to the hormonal system . Damage to the islets of Langerhans can result in diabetes mellitus or hyperinsulinism .
Layout and function
Overall, the islets of Langerhans make up about one to two percent of the mass of the pancreas; a healthy adult has about a million of these mini-organs. Each “island” has a diameter of 0.2-0.5 mm. The hormones produced by the various islet cells are released directly into the blood.
The insulin-producing beta cells ( β cells) make up 65 to 80 percent of the islet cells. Their functions are:
- Synthesis of insulin and its provision in secretory vesicles ,
- Register the blood sugar level,
- with increased blood sugar levels (> 5.6 mM glucose . eg after meals) release of insulin into the blood until the blood sugar level to normal.
In addition to the β -cells in a pancreatic islet or the glucagon -producing alpha cells ( α cells) (15 to 20 percent), somatostatin -producing delta cells ( δ cells) (three to ten percent), pancreatic polypeptide containing Ghrelin or ε cells containing PP cells and ghrelin .
Islets of Langerhans have a particularly dense network of small blood vessels ( capillary network ) with a specialized structure. The endothelial cells forming the capillaries have small windows (so-called fenestrated endotheles ) through which the endocrine cells, such as e.g. B. the β cells, are in direct contact with the blood. This allows z. For example, the β cells "feel" the blood sugar level and, if necessary, release the insulin directly into the blood.
After birth , new β cells are created by dividing existing β cells. It is possible that new β cells can also arise from other cell types present in the pancreas . The total mass of β- cells in the pancreas can also be adapted in adulthood to an increased need for insulin (e.g. during pregnancy or if the patient becomes increasingly overweight), whereby the peptide hormone betatrophin, which is synthesized in the liver, may play a role.
With reduced expression of the important transcription factor FOXO1 , as in severe hyperglycaemia , the gene expression of typical β- cell genes such as those for insulin, glucose transporter 2 and glucokinase is reduced . Due to the high islet cell plasticity, the Foxo1-deficient β- cells can finally develop a gene expression that corresponds to that of other islet cells, such as that of the glucagon-producing α- cells, which leads to the reduced number of β- cells and the simultaneous hyperfunction of α - Cells in type 2 diabetes mellitus explained.
transplantation
As with any other tissues also, one attempts had made to islet cell transplant . For the transplant, the whole pancreas is usually no longer transplanted, but only the islet cells, which are obtained through a special washing process. Here, however, one encounters the same rejection reactions as can also be found in other tissues. Since cyclosporine , however, and other drugs to prevent rejection liver - and kidney toxic effect, these drugs also have a kidney transplant may be necessary by taking already about ten years after islet cell transplantation. However, since long-term diabetics can remain free of long-term damage until the end of their lives even after 40 years of insulin therapy , this risk is disproportionately high.
See also
Web links
Individual evidence
- ↑ Michael Sachs: Langerhanssche Islands. In: Werner E. Gerabek , Bernhard D. Haage, Gundolf Keil , Wolfgang Wegner (eds.): Enzyklopädie Medizingeschichte. De Gruyter, Berlin / New York 2005, ISBN 3-11-015714-4 , p. 824 f.
- ↑ Paul Langerhans: Contribution to the microscopic anatomy of the pancreas. Medical dissertation Berlin 1869.
- ^ Philip A. Seymour, Palle Serup: Bulking Up on Beta Cells . New England Journal of Medicine 2013, Volume 369, Issue 8, Aug. 22, 2013, pages 777-779; doi : 10.1056 / NEJMcibr1307038 .
- ↑ Yuval Dor, Benjamin Glaser: Beta-Cell Dedifferentiation and Type 2 Diabetes . New England Journal of Medicine 2013; Volume 368, issue 6 of February 7, 2013, pages 572-573, doi : 10.1056 / NEJMcibr1214034 .