Islets of Langerhans
| Pancreatic islets | |
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Pancreatic islet (mouse) in its typical proximity to a blood vessel; insulin in red, nuclei in blue.
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| Details | |
| Identifiers | |
| Latin | insulae pancreaticae |
| TA | A05.9.01.019 |
| FMA | 16016 76489, 16016 |
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Anatomical terminology
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The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (i.e., hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. New studies show that the pancreatic islets constitute approximately 4.5% of the pancreas volume and receive 10-15% of its blood flow. The islets of Langerhans are arranged in density routes throughout the healthy human pancreas.
There are about 3 million islets distributed in the form of density routes throughout the pancreas of a healthy adult human, each of which measures an average of about 0.1 mm (109 µm) in diameter.:914 Each is separated from the surrounding pancreatic tissue by a thin fibrous connective tissue capsule which is continuous with the fibrous connective tissue that is interwoven throughout the rest of the pancreas.:914 The combined mass of the islets is 2 grams. Islets of Langerhans can also form super structures called Islet clusters which are composed of small islets that surround large blood vessels. The roundness of islets along the pancreas has also been quantified through the Index of Sphericity method. Thus, the islets closest to the spherical form are mainly found in the pancreas tail whereas the islets farthest from the spherical form are found in the pancreas neck.
Hormones produced in the pancreatic islets are secreted directly into the blood flow by (at least) five types of cells. In rat islets, endocrine cell subsets are distributed as follows:
It has been recognized that the cytoarchitecture of pancreatic islets differs between species. In particular, while rodent islets are characterized by a predominant proportion of insulin-producing beta cells in the core of the cluster and by scarce alpha, delta and PP cells in the periphery, human islets display alpha and beta cells in close relationship with each other throughout the cluster.
Islets can influence each other through paracrine and communication, and beta cells are coupled electrically to other beta cells (but not to other cell types).
The paracrine feedback system of the pancreatic islets has the following structure:
A large number of G protein-coupled receptors (GPCRs) regulate the secretion of insulin, glucagon and somatostatin from pancreatic islets, and some of these GPCRs are the targets of drugs used to treat type-2 diabetes (ref GLP-1 receptor agonists, DPPIV inhibitors).b
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