Editing Pancreas (section)

===Blood glucose regulation===
{{See also|Pancreatic islets}}
[[File:Negative Feedback Gif.gif|thumb|The pancreas maintains constant blood glucose levels (shown as the waving line). When the blood glucose level is too high, the pancreas secretes insulin and when the level is too low, the pancreas secretes glucagon.]]
Cells within the pancreas help to maintain blood glucose levels ([[homeostasis]]). The cells that do this are located within the pancreatic islets that are present throughout the pancreas. When blood glucose levels are low, [[alpha cell]]s secrete [[glucagon]], which increases blood glucose levels. When blood glucose levels are high [[beta cell]]s secrete [[insulin]] to decrease glucose in blood. [[Delta cell]]s in the islet also secrete [[somatostatin]] which decreases the release of insulin and glucagon.{{sfn|Wheater's Histology|2013|pp=332-333}}

Glucagon acts to increase glucose levels by promoting the [[gluconeogenesis|creation of glucose]] and the [[glycogenolysis|breakdown of glycogen]] to glucose in the liver. It also decreases the uptake of glucose in fat and muscle. Glucagon release is stimulated by low blood glucose or insulin levels, and during exercise.{{sfn|Harrison's|2015|pp=2853-4}} Insulin acts to decrease blood glucose levels by facilitating uptake by cells (particularly [[skeletal muscle]]), and promoting its use in the creation of proteins, fats and carbohydrates. Insulin is initially created as a precursor form called [[preproinsulin]]. This is converted to [[proinsulin]] and cleaved by [[C-peptide]] to [[insulin]] which is then stored in granules in beta cells. Glucose is taken into the beta cells and degraded. The end effect of this is to cause [[depolarisation]] of the cell membrane which stimulates the release of the insulin.{{sfn|Harrison's|2015|pp=2853-4}}

<!--Influences-->The main factor influencing the secretion of insulin and glucagon are the levels of glucose in blood plasma.<ref name=Ganongs2019Islets>{{Cite book|title=Ganong's review of medical physiology|author1=Barrett, Kim E.|others=Barman, Susan M.,, Brooks, Heddwen L., Yuan, Jason X.-J.|isbn=978-1-260-12240-4|edition=26th|location=New York|oclc=1076268769|year=2019|pages=433–437|section=Regulation of Insulin Secretion; Glucagon}}</ref> Low blood sugar stimulates glucagon release, and high blood sugar stimulates insulin release. Other factors also influence the secretion of these hormones. Some [[amino acid]]s, that are byproducts of the digestion of [[protein]], stimulate insulin and glucagon release. Somatostatin acts as an inhibitor of both insulin and glucagon. The [[autonomic nervous system]] also plays a role. Activation of [[Beta-2 adrenergic receptor|Beta-2 receptors]] of the [[sympathetic nervous system]] by [[catecholamine]]s secreted from sympathetic nerves stimulates secretion of insulin and glucagon,<ref name=Ganongs2019Islets /><ref name=GuytonHall2016>{{cite book |last1=Hall |first1=John E |title=Guyton and Hall textbook of medical physiology |date=2016 |publisher=Elsevier |location=Philadelphia |isbn=978-1-4557-7016-8 |edition=13th|pages=990–994}}</ref> whereas activation of [[Alpha-1 adrenergic receptors|Alpha-1 receptors]] inhibits secretion.<ref name=Ganongs2019Islets /> [[Muscarinic acetylcholine receptor M3|M3 receptors]] of the [[parasympathetic nervous system]] act when stimulated by the right [[vagus nerve]] to stimulate release of insulin from beta cells.<ref name=Ganongs2019Islets />