Intrinsic factor - wikipedia Intrinsic factor GIF Available structures PDB Ortholog search : PDBe RCSB List of PDB id codes 2PMV, 3KQ4 Identifiers Aliases GIF, IF, IFMH, INF, TCN3, gastric intrinsic factor, intrinsic factor, Intrinsic factor, IF External IDs OMIM : 609342 MGI : 1202394 HomoloGene : 3773 GeneCards : GIF Gene location ( Human ) Chr. Chromosome 11 ( human ) Band 11q12. 1 Start 59,829,268 bp End 59,845,501 bp Gene location ( Mouse ) Chr. Chromosome 19 ( mouse ) Band 19 19 A Start 11,747,554 bp End 11,763,447 bp Gene ontology Molecular function cobalamin binding Cellular component extracellular region microvillus endosome lysosomal lumen apical plasma membrane extracellular space Biological process cobalt ion transport ion transport cobalamin transport cobalamin metabolic process Sources : Amigo / QuickGO Orthologs Species Human Mouse Entrez 2694 14603 Ensembl ENSG00000134812 ENSMUSG00000024682 UniProt P27352 P52787 RefSeq ( mRNA ) NM_005142 NM_008118 RefSeq ( protein ) NP_005133 NP_032144 Location ( UCSC ) Chr 11 : 59.83 -- 59.85 Mb Chr 11 : 11.75 -- 11.76 Mb PubMed search Wikidata View / Edit Human View / Edit Mouse Intrinsic factor ( IF ), also known as gastric intrinsic factor ( GIF ), is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the ileum of the small intestine. In humans, the gastric intrinsic factor protein is encoded by the GIF gene. Haptocorrin ( also known as HC, R protein, and transcobalamin I, TCN1 ) is another glycoprotein secreted by the salivary glands which binds to vitamin B. Vitamin B is acid sensitive and in binding to transcobalamin I it can safely pass through the acidic stomach to the duodenum. In the less acidic environment of the small intestine, pancreatic enzymes digest the glycoprotein carrier and vitamin B can then bind to intrinsic factor. This new complex is then absorbed by the epithelial cells ( enterocytes ) of the ileum. Inside the cells, B dissociates once again and binds to another protein, transcobalamin II ( TCN2 ) ; the new complex can then exit the epithelial cells to be carried to the liver. Contents 1 Site of secretion 2 Insufficiency 3 Treatment 4 References 5 Further reading 6 External links Site of secretion The intrinsic factor is secreted by the stomach, and so is present in the gastric juice as well as in the gastric mucous membrane. The optimum pH for its action is approximately 7. Its concentration does not correlate with the amount of HCl or pepsin in the gastric juice, e.g., intrinsic factor may be present even when pepsin is largely absent. The site of formation of the intrinsic factor varies in different species. In pigs it is obtained from the pylorus and beginning of the duodenum ; in human beings it is present in the fundus and body of the stomach. The limited amount of normal human gastric intrinsic factor limits normal efficient absorption of B to about 2 μg per meal, a nominally adequate intake of B. Insufficiency In pernicious anemia, which is usually an autoimmune disease, autoantibodies directed against intrinsic factor or parietal cells themselves lead to an intrinsic factor deficiency, malabsorption of vitamin B, and subsequent megaloblastic anemia. Atrophic gastritis can also cause intrinsic factor deficiency and anemia through damage to the parietal cells of the stomach wall. Pancreatic exocrine insufficiency can interfere with normal dissociation of vitamin B from its binding proteins in the small intestine, preventing its absorption via the intrinsic factor complex. Other risk factors contributing to pernicious anemia are anything that damages or removes a portion of the stomach 's parietal cells, including bariatric surgery, gastric tumors, gastric ulcers, and excessive consumption of alcohol. Mutations in the GIF gene are responsible for a rare inheritable disease called intrinsic factor deficiency which results in malabsorption of vitamin B. Treatment In most countries, intramuscular injections of vitamin B are used to treat pernicious anemia. Orally administered vitamin B is absorbed without intrinsic factor, but at levels of less than one percent than if intrinsic factor is present. Despite the low amounts absorbed, oral vitamin B therapy is effective at reducing symptoms of pernicious anemia. Vitamin B can also be given sublingually, but there is no evidence that this route of administration is superior to the oral route. Despite evidence of efficacy of oral vitamin B treatment, only Canada and Sweden routinely prescribe this route of administration. References ^ Jump up to : GRCh38 : Ensembl release 89 : ENSG00000134812 - Ensembl, May 2017 ^ Jump up to : GRCm38 : Ensembl release 89 : ENSMUSG00000024682 - Ensembl, May 2017 Jump up ^ `` Human PubMed Reference : ''. Jump up ^ `` Mouse PubMed Reference : ''. Jump up ^ Pocock G, Richards C ( 2006 ). Human Physiology : The Basis of Medicine ( 3rd ed. ). Oxford University Press. p. 230. ISBN 978 - 019 - 856878 - 0. ^ Jump up to : Alpers DH, Russell - Jones G ( May 2013 ). `` Gastric intrinsic factor : the gastric and small intestinal stages of cobalamin absorption. a personal journey ''. ( review ). Biochimie. 95 ( 5 ) : 989 -- 94. doi : 10.1016 / j. biochi. 2012.12. 006. PMID 23274574. ^ Jump up to : Fedosov SN ( 2012 ). `` Physiological and molecular aspects of cobalamin transport ''. ( review ). Sub-Cellular Biochemistry. 56 : 347 -- 67. doi : 10.1007 / 978 - 94 - 007 - 2199 - 9_18. PMID 22116708. Jump up ^ Sharma K ( 2016 ). `` Gastrointestinal System ''. In Talwar G, Hasnain SE, Sarin SK. Textbook Of Biochemistry, Biotechnology, Allied And Molecular Medicine. ( secondary ) ( 4th ed. ). PHI Learning Private Limited. p. 632. ISBN 978 - 81 - 203 - 5125 - 7. Jump up ^ Shum HY, O'Neill BJ, Streeter AM ( 1971 ). `` Effect of pH changes on the binding of vitamin B12 by intrinsic factor ''. Journal of Clinical Pathology. 24 ( 3 ) : 239 -- 43. doi : 10.1136 / jcp. 24.3. 239. PMC 476962. PMID 5103294. Jump up ^ Poliner IJ, Spiro HM, Pask BA, Trocchio N ( 1958 ). `` The independent secretion of acid, pepsin, and intrinsic factor by the human stomach ''. ( primary ). Gastroenterology. 34 ( 2 ) : 196 -- 209. doi : 10.1016 / S0016 - 5085 ( 58 ) 80102 - X. PMID 13512593. Jump up ^ Heatley NG, Florey H, Turnbull A, Jennings MA, Watson GM, Wakisaka G, Witts LJ ( 1954 ). `` Intrinsic factor in the pyloric and duodenal secretions of the pig ''. ( primary ). Lancet. 267 ( 6838 ) : 578 -- 80. doi : 10.1016 / S0140 - 6736 ( 54 ) 90355 - 4. PMID 13193076. Jump up ^ Howard TA, Misra DN, Grove M, Becich MJ, Shao JS, Gordon M, Alpers DH ( 1996 ). `` Human gastric intrinsic factor expression is not restricted to parietal cells ''. ( primary ). Journal of Anatomy. 189 ( Pt 2 ) : 303 -- 13. PMC 1167747. PMID 8886952. Jump up ^ Watanabe F ( Nov 2007 ). `` Vitamin B12 sources and bioavailability ''. ( review ). Experimental Biology and Medicine. 232 ( 10 ) : 1266 -- 74. doi : 10.3181 / 0703 - MR - 67. PMID 17959839. Jump up ^ Osborne D, Sobczyńska - Malefora A ( 2015 ). `` Autoimmune mechanisms in pernicious anaemia & thyroid disease ''. ( review ). Autoimmunity Reviews. 14 ( 9 ) : 763 -- 8. doi : 10.1016 / j. autrev. 2015.04. 011. PMID 25936607. Jump up ^ Neumann WL, Coss E, Rugge M, Genta RM ( 2013 ). `` Autoimmune atrophic gastritis -- pathogenesis, pathology and management ''. ( review ). Nature Reviews. Gastroenterology & Hepatology. 10 ( 9 ) : 529 -- 41. doi : 10.1038 / nrgastro. 2013.101. PMID 23774773. Jump up ^ Guéant JL, Champigneulle B, Gaucher P, Nicolas JP ( 1990 ). `` Malabsorption of vitamin B12 in pancreatic insufficiency of the adult and of the child ''. ( review ). Pancreas. 5 ( 5 ) : 559 -- 67. doi : 10.1097 / 00006676 - 199009000 - 00011. PMID 2235967. Jump up ^ Kozyraki R, Cases O ( 2013 ). `` Vitamin B12 absorption : mammalian physiology and acquired and inherited disorders ''. ( review ). Biochimie. 95 ( 5 ) : 1002 -- 7. doi : 10.1016 / j. biochi. 2012.11. 004. PMID 23178706. ^ Jump up to : Shipton MJ, Thachil J ( 2015 ). `` Vitamin B12 deficiency - A 21st century perspective ''. ( review ). Clinical Medicine. 15 ( 2 ) : 145 -- 50. doi : 10.7861 / clinmedicine. 15 - 2 - 145. PMID 25824066. Jump up ^ Alpers DH ( Mar 2005 ). `` What is new in vitamin B ( 12 ) ? ''. ( review ). Current Opinion in Gastroenterology. 21 ( 2 ) : 183 -- 6. doi : 10.1097 / 01. mog. 0000148331.96932. 44. PMID 15711210. Jump up ^ Andrès E, Fothergill H, Mecili M ( 2010 ). `` Efficacy of oral cobalamin ( vitamin B12 ) therapy ''. ( review ). Expert Opinion on Pharmacotherapy. 11 ( 2 ) : 249 -- 56. doi : 10.1517 / 14656560903456053. PMID 20088746. Jump up ^ Sharabi A, Cohen E, Sulkes J, Garty M ( 2003 ). `` Replacement therapy for vitamin B12 deficiency : comparison between the sublingual and oral route ''. ( primary ). British Journal of Clinical Pharmacology. 56 ( 6 ) : 635 -- 8. doi : 10.1046 / j. 1365 - 2125.2003. 01907. x. PMC 1884303. PMID 14616423. Further reading Devalia V, Hamilton MS, Molloy AM ( Aug 2014 ). `` Guidelines for the diagnosis and treatment of cobalamin and folate disorders ''. ( review ). British Journal of Haematology. 166 ( 4 ) : 496 -- 513. doi : 10.1111 / bjh. 12959. PMID 24942828. Coati I, Fassan M, Farinati F, Graham DY, Genta RM, Rugge M ( Nov 2015 ). `` Autoimmune gastritis : Pathologist 's viewpoint ''. ( review ). World Journal of Gastroenterology. 21 ( 42 ) : 12179 -- 89. doi : 10.3748 / wjg. v21. i42. 12179. PMC 4641135. PMID 26576102. Quadros EV ( Jan 2010 ). `` Advances in the understanding of cobalamin assimilation and metabolism ''. ( review ). British Journal of Haematology. 148 ( 2 ) : 195 -- 204. doi : 10.1111 / j. 1365 - 2141.2009. 07937. x. PMC 2809139. PMID 19832808. Christensen EI, Nielsen R, Birn H ( Feb 2013 ). `` From bowel to kidneys : the role of cubilin in physiology and disease ''. ( review ). Nephrology, Dialysis, Transplantation. 28 ( 2 ) : 274 -- 81. doi : 10.1093 / ndt / gfs565. PMID 23291372. External links Intrinsic factor at the US National Library of Medicine Medical Subject Headings ( MeSH ) MedlinePlus Encyclopedia 002381 Overview at colostate.edu Physiology of the gastrointestinal system GI tract Upper Exocrine Chief cells Pepsinogen Parietal cells Gastric acid Intrinsic factor Foveolar cells HCO Mucus Goblet cells Mucus Processes Swallowing Vomiting Fluids Saliva Gastric acid Lower Enteric nervous system Submucous plexus Myenteric plexus Endocrine / paracrine G cells gastrin D cells somatostatin ECL cells Histamine enterogastrone : I cells CCK K cells GIP S cells secretin Enteroendocrine cells Enterochromaffin cell APUD cell Fluids Intestinal juice Processes Segmentation contractions Migrating motor complex Borborygmus Defecation Either / both Processes Peristalsis ( Interstitial cell of Cajal Basal electrical rhythm ) Gastrocolic reflex Digestion Enterocyte Accessory Fluids Bile Pancreatic juice Processes Enterohepatic circulation Abdominopelvic Peritoneal fluid Protein, glycoconjugate : glycoproteins and glycopeptides Mucoproteins Mucin CD43 CD164 MUC1 MUC2 MUC3A MUC3B MUC4 MUC5AC MUC5B MUC6 MUC7 MUC8 MUC12 MUC13 MUC15 MUC16 MUC17 MUC19 MUC20 Other Haptoglobin Intrinsic factor Orosomucoid Peptidoglycan Phytohaemagglutinin Ovomucin Proteoglycans CS / DS Decorin Biglycan Versican HS / CS Testican Perlecan CS Chondroitin sulfate proteoglycans : Aggrecan Neurocan Brevican CD44 CSPG4 CSPG5 Platelet factor 4 Structural maintenance of chromosomes 3 KS Fibromodulin Lumican Keratocan HS Syndecan 1 Other Activin and inhibin ADAM Alpha 1 - antichymotrypsin Apolipoprotein H CD70 Asialoglycoprotein Avidin B - cell activating factor 4 - 1BB ligand Cholesterylester transfer protein Clusterin Colony - stimulating factor Hemopexin Lactoferrin Membrane glycoproteins Myelin protein zero Osteonectin Protein C Protein S Serum amyloid P component Sialoglycoprotein CD43 Glycophorin Glycophorin C Thrombopoietin Thyroglobulin Thyroxine - binding proteins Transcortin Tumor necrosis factor alpha Uteroglobin Vitronectin Retrieved from `` https://en.wikipedia.org/w/index.php?title=Intrinsic_factor&oldid=823348635 '' Categories : Genes on human chromosome 11 Hematology Gastroenterology Genes mutated in mice Stomach Talk Contents About Wikipedia Català Deutsch Español فارسی Français Italiano עברית Nederlands 日本 語 Polski Português Русский Simple English Suomi Svenska Türkçe Українська 粵語 中文 Edit links This page was last edited on 31 January 2018, at 18 : 45. 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Question: where is b12 absorbed in the gi tract
Answer: in the ileum of the small intestine