# Gastrointestinal hormone

The gastrointestinal hormones (or gut hormones) constitute a group of hormones secreted by enteroendocrine cells in the stomach, pancreas, and small intestine that control various functions of the digestive organs. Later studies showed that most of the gut peptides, such as secretin, cholecystokinin or substance P, were found to play a role of neurotransmitters and neuromodulators in the central and peripheral nervous systems.
Enteroendocrine cells do not form glands but are spread throughout the digestive tract. They exert their autocrine and paracrine actions that integrate gastrointestinal function.

## Types

The gastrointestinal hormones can be divided into three main groups based upon their chemical structure.
* Gastrin–cholecystokinin family: gastrin and cholecystokinin
* Secretin family: secretin, glucagon, vasoactive intestinal peptide and gastric inhibitory peptide
* Somatostatin family
* Motilin family
* Substance P.
Ghrelin is a peptide hormone released from the stomach and liver and is often referred to as the "hunger hormone" since high levels of it are found in individuals that are fasting. Ghrelin agonistic treatments can be used to treat illnesses such as anorexia and loss of appetites in cancer patients. Ghrelin treatments for obesity are still under intense scrutiny and no conclusive evidence has been reached. This hormone stimulates growth hormone release. Amylin controls glucose homeostasis and gastric motility
Glucose-dependent insulinotropic polypeptide possesses an acute influence on food intake through its effects on adipocytes
Oxyntomodulin plays a role in controlling acid secretion and satiation
Characteristics of prominent forms of principal gut regulatory peptides$^{:1719}$ :
| Hormone or peptide | Molecular weight (Da) | Number of amino acids | Main gut localization | Principal physiologic actions |
| Gastrin family | | | | |
| Cholecystokinin | 3918 | 33 (also 385, 59) | Duodenum and jejunum, Enteric nerves | Stimulates gallbladder contraction and intestinal motility; stimulates secretion of pancreatic enzymes, insulin, glucagon, and pancreatic polypeptides; has a role in indicating satiety; the C-terminal 8 amino acid peptide cholecystokinin (CCK)-8 retains full activity |
| Little gastrin | 2098 | 17 | Both forms of gastrin are found in the gastric antrum and duodenum | Gastrins stimulate the secretion of gastric acid, pepsinogen, intrinsic factor, and secretin; stimulate intestinal mucosal growth; increase gastric and intestinal motility |
| Big gastrin | 3839 | 34 | Both forms of gastrin are found in the gastric antrum and duodenum | Gastrins stimulate the secretion of gastric acid, pepsinogen, intrinsic factor, and secretin; stimulate intestinal mucosal growth; increase gastric and intestinal motility |
| Secretin-glucagon family | | | | |
| Secretin | 3056 | 27 | Duodenum and jejunum | Stimulates pancreatic secretion of HCO$_3$, enzymes and insulin; reduces gastric and duodenal motility, inhibits gastrin release and gastric acid secretion |
| Vasoactive intestinal polypeptide (VIP) | 3326 | 28 | Enteric nerves | Relaxes smooth muscle of gut, blood vessels, and genitourinary system; increases water and electrolyte secretion from pancreas and gut; releases hormones from pancreas, gut, and hypothalamus |
| Glucose-dependent insulinotropic | 4976 | 42 | Duodenum and jejunum | Stimulates insulin release; reduces gastric and intestinal motility; increases fluid and electrolyte secretion from small intestine |
Brief Description of Some GI Regulatory Peptides$^{:1720}$ :
| Hormone or peptide | Major tissue locations in the gut | Principal known actions |
| Bombesin | Throughout the gut and pancreas | Stimulates release of cholecystokinin (CCK) and gastrin |
| Calcitonin gene-related peptide | Enteric nerves | Unclear |
| Chromogranin A | Neuroendocrine cells | Secretory protein |
| Enkephalins | Stomach, duodenum | Opiate-like actions |
| Enteroglucagon | Small intestine, pancreas | Inhibits insulin secretion |
| Galanin | Enteric nerves | |
| Ghrelin | Stomach | Stimulates appetite, increases gastric emptying |
| Glucagon-like peptide 1 | Pancreas, ileum | Increases insulin secretion |
| Glucagon-like peptide 2 | Ileum, colon | Enterocyte-specific growth hormone |
| Growth factors | Throughout the gut | Cell proliferation and differentiation |
| Growth hormone-releasing factor | Small intestine | Unclear |
| Leptin | Stomach | Appetite control |
| Motilin | Throughout the gut | Increases gastric emptying and small bowel motility |
| Neuropeptide Y | Enteric nerves | Regulation of intestinal blood flow |
| Neurotensin | Ileum | Affects gut motility; increases jejunal and ileal fluid secretion |
| Pancreatic polypeptide | Pancreas | Inhibits pancreatic and biliary secretion |
| Peptide YY | Colon | Inhibits food intake |
| Somatostatin | Stomach, pancreas | Inhibits secretion and action of many hormones |
| Substance P | Enteric nerves | Unclear |
| Trefoil peptides | Stomach, intestine | Mucosal protection and repair |