Pancreatic islets

The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1 to 2% of the pancreas volume and receive 10–15% of its blood flow. The pancreatic islets are arranged in density routes throughout the human pancreas, and are important in the metabolism of glucose.A pancreatic islet, stained.A pancreatic islet, showing alpha cellsA pancreatic islet, showing beta cells.Mouse islet immunostained for pancreatic polypeptideMouse islet immunostained for insulinMouse islet immunostained for glucagonPancreatic islets, the lighter tissue among the darker, acinar pancreatic tissue, hemalum-eosin stain.Illustration of dog pancreas. 250x.Structural differences between rat islets (top) and humans islets (bottom) as well as the ventral part (left) and the dorsal part (right) of the pancreas. Different cell types are colour-coded. Rodent islets, unlike the human ones, show the characteristic insulin core. The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1 to 2% of the pancreas volume and receive 10–15% of its blood flow. The pancreatic islets are arranged in density routes throughout the human pancreas, and are important in the metabolism of glucose. 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 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 autocrine communication, and beta cells are coupled electrically to six to seven 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). Electrical activity of pancreatic islets has been studied using patch clamp techniques. It has turned out that the behavior of cells in intact islets differs significantly from the behavior of dispersed cells. The beta cells of the pancreatic islets secrete insulin, and so play a significant role in diabetes. It is thought that they are destroyed by immune assaults. However, there are also indications that beta cells have not been destroyed but have only become non-functional.