Intestine endocrine cells

The hormone peptide YY (PYY) is a 36 amino acid peptide, which is closely related to neuropeptide Y and pancreatic polypeptide. PYY is predominantly synthesised and released by intestinal endocrine cells, and can also coexist with glucagon in pancreatic acini and enteroglucagon in endocrine cells of the lower bowel. It acts on the same receptors as neuropeptide Y. The endogenous long C-terminal PYY fragment PYY3 36 is a biologically active and subtype-selective metabolite. 

Lauweryns JM, Van Ranst L. Immunohistochemical localization of aromatic-L-amino acid decarboxylase in human, rat and mouse broncho-pulmonary and gastro-intestinal endocrine cells. J Histoohem Cytochem 1988 36 1181-1186. 

Neuropeptides Y (NFY) and YY are 36-residue amidated peptides that are members of the pancreatic polypeptide (PP) family (Fig. 30-5). NPY is produced both in the peripheral nervous system and in the brain,110 134 where it is one of the most abundant neuropeptides. Another member of the PP family is semi-nalplasmin, a regulator of calcium ion transport in bovine sperm.135 NPY is best known for its stimulation of appetite. It also inhibits anxiety and increases memory retention. It has a vasoconstrictive effect on blood vessels, participating in cardiovascular regulation.136 137 Peptide YY is formed in endocrine cells of the intestine, while NPY is formed in neurons of the parasympathetic system.138 Both participate in regulation of fluid and electrolyte secretion. Both are found in other vertebrate species.139... 

As mentioned above, the villi of the small intestine (Figure 1.2) house a dynamic, self-renewing population of the epithelial cells that includes absorptive cells (enterocytes), secretory cells, and endocrine cells. The thin lining (height 25 p,M height of the microvilli is 1.5 pM) of the columnar enterocytes is the only barrier between the intestinal lumen and the muscularis mucosa, which represents, in this context, the entire body interior. The entire epithelial lining of the intestine replaces itself every 3-5 d [128], It is the enterocyte and its neighboring cells where absorption processes occur and it will therefore be the focus of the mechanistic discussions below. 

A gut hormone present in endocrine cells in the lower intestine that can be released by the presence of luminal free fatty acids. 

Neurotensin is an endogenous peptide neurotransmitter inducing a variety of effects, including analgesia, hypothermia, and increased locomotor activity. It is also involved in regulation of dopamine pathways. Neurotensin is found in endocrine cells of the small intestine, where it leads to secretion and smooth muscle contraction (Moore and Black, 1991). 

Secretin and CCK are secreted by cells of the duodenum, the segment of the small intestine directly connected to the stomach. The endocrine cells of the duodenum include the I cells and S cells. The I cells secrete CCK, a hormone that enters the bloodstream, through which it reaches a variety of organs. Some of these organs, such as the stomach, gall bladder, and pancreas, contain CCK receptors on their plasma membranes, CCK binds to these receptors and generates a number of... 

A one-cell thick sheet of epithelial cells covers the surfaces of the villi and lines of crypts. Some of the cell types identified in the epithelial lining of the small intestine are enterocytes (digestion and absorption), goblet cells (mucus secretion), endocrine cells (hormone secretion), and M cells (absorption of food and antigens). 

The gut contains a collection of nerves called the enteric nervous system. Various activities of the gut, such as peristaltic contractions, and certain activities of the pancreas and gall bladder, are controlled in a manner that is relatively independent of the central nervous system. The central nervous system consists of the brain and spinal cord. Five types of activity are controlled by the enteric nervous system (1) contraction of smooth muscles that create the peristaltic waves used to mix and propel food through the intestines (2) release of juices by secretory cells (3) release of hormones from endocrine cells of the gut (4) patterns of blood flow through the arteries of the gut [variations in blood flow occur because of the opening of blood vessels (vasodilation) or the closing of blood vessels (vasoconstriction)] and (5) activities of immune cells of the gut (Goyal and Hirano, 1996). 

Gastric acid secretion can be inhibited by several mechanisms including acid in the stomach (pH 3 inhibits gastrin release), acid in the duodenum, the presence of fat in the pancreas, and hypertonic fluids or hyperglycemia. Somatostatin, a hormone produced by antral mucosal endocrine cells (D cells), inhibits the release of gastrin by directly inhibiting the parietal cells. Somatostatin is also present in other GI tissue and the pancreas. C cells, endocrine cells in the proximal small intestine, secrete secretin in response to mucosal acidification, which also decreases gastric secretion. 

Fig. 15. Hypothetical model of how initiators and modulators that affect insulin release may reach A-, B- and D-cells. The first target of arterial blood containing nutrients, hormones, peptides and drugs is the B-cell. From there, via an intraislet portal vein system, blood which now also contains released insulin flows to the mantle where A- and D-cells are localized and from there enters the circulation. Nerves derived from the autonomous nervous system which contain neurotransmitters (acetylcholine, noradrenaline) and neuropeptides (including vasoactive intestinal peptide (VIP), gastrin-releasing peptide (GRP), galanin) are connected to islet cells. Glucagon (A-cells) and somatostatin (D-cells) reach other endocrine cells in the islet in a paracrine manner. The B-cell may also be the target of previously released insulin via a short loop.

PIT3-36, which, though related chemically to the orexigenic neuropeptide Y (see below), is functionally an anorexic peptide. It is secreted by endocrine cells lining the distal small intestine and upper colon in amounts proportional to the calorie content of the food consumed (Bat-terham et al. 2002). In humans, infusion of normal postprandial concentrations of PYY(3-36) significantly decreases appetite and reduces food intake by 33% over 24 h. It possibly acts through the arcuate nucleus. 

Endocrine cells are distributed throughout the small intestine and other sections of the GI tract. About 20 different cell types have been identified. Some, easily identifiable by their staining characteristics, are argentaffin or ente-rochromaffin cells containing 5-hydroxytryptophan, the precursor of serotonin (Chapter 17). Neoplastic transformation of these cells leads to excessive production and secretion of serotonin, which causes diarrhea, flushing, and bronchoconstriction carcinoid syndrome). Other types of cells lack 5-hydroxytryptophan but take up amine precursors (e.g., amino acids) to synthesize and store biologically active peptides (e.g., hormones). 

Chyme contains potent secretagogues for various endocrine cells in the intestinal mucosa. CCK and secretin cause release of an alkaline pancreatic juice containing trypsinogen, chymotrypsinogen, proelastase, and procarboxypeptidases A and B. Activation begins with that of trypsinogen to trypsin by enteropeptidase (previously called enterokinase) present in the brush-border membranes of the duodenum. 

Dayal Y. Endocrine cells of the gut and their neoplasms. In Norris HT, ed. Pathology of the Colon, Small Intestine and Anus. New York Churchill Livingstone 1991 305-366. 

As expected, virtually all IPMNs express CKs. They are positive for CAM 5.2, AE1/AE3, CKs 7, 8, 18, 19, and variably for CK20. > 7198 Some IPMNs, especially villous/intestinal type, also express CA19-9 and CEA. 2°° In the villous/intestinal type, the degree of CEA expression increases with the degree of dysplasia. " Twenty percent of IPMNs label for DUPAN-2. > > Scattered endocrine cells that are positive with chro-mogranin and synaptophysin are seen in most tumors but account for less than 5% of the tumor cells. Cyclooxygenase-2 is also expressed in 60% to 80% of IPMNs. 204... 

Endocrine cells are commonly found in ampullary adenocarcinomas. Although they may not be evident by routine microscopy, immunohistochemical staining for chromogranin reveals scattered endocrine cells in one third of the cases. The distribution of these neuroendocrine cells is random in some cases they are scattered evenly throughout the tumor, whereas in others they may be clustered. In general, they are more common in intestinal-type or mucinous adenocarcinomas than in pancreatobiliary type. ... 

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