Intrinsic factor
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Overview
| gastric intrinsic factor
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| Identifiers | |
| Symbol | GIF |
| Entrez | 2694 |
| HUGO | 4268 |
| OMIM | 609342 |
| RefSeq | NM_005142 |
| UniProt | P27352 |
| Other data | |
| Locus | Chr. 11 q13 |
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Intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the terminal ileum.
Upon entry into the stomach, vitamin B12 becomes bound to one of two B12 binding proteins present in gastric juice. In the less acidic environment of the small intestine, these proteins dissociate from the vitamin, enabling it to bind to intrinsic factor and enter the portal circulation through a receptor in the ileal mucosa specific for the B12-intrinsic factor complex.
Clinical significance
In pernicious anemia, an autoimmune disease, autoantibodies directed against intrinsic factor or parietal cells themselves lead to an intrinsic factor deficiency, malabsorption of vitamin B12, 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 B12 from its binding proteins in the small intestine, preventing its absorption via the intrinsic factor complex.
Bariatric surgery is a known risk factor in the development of pernicious anemia. Other risk factors contributing to this condition are stomach tumors, gastric ulcers, and excessive consumption of alcohol.
Note
Patients experiencing an insufficiency in their intrinsic factor levels cannot benefit from a low dose oral vitamin B-12 supplement, because it will not absorb through the wall of the small intestine. Historically, the disease was thought untreatable before the discovery that it could be managed with regular injections of vitamin B-12, thus bypassing the digestive tract. More recently, Swedish researchers discovered that sufficiently large doses of B-12 can also be absorbed sublingually, so injections are necessary only for those unable to take pills by sublingual administration.
External links
Digestive system, physiology: gastrointestinal physiology | |
|---|---|
| Enteric nervous system | Meissner's plexus - Auerbach's plexus |
| Exocrine | Chief cells (Pepsinogen) - Parietal cells (Gastric acid, Intrinsic factor) - Goblet cells (Mucus) |
| Endocrine/paracrine | G cells (gastrin), D cells (somatostatin) - ECL cells (Histamine) - enterogastrone: I cells (CCK), K cells (GIP), S cells (secretin) |
| Border | Brunner's glands - Paneth cells - Enterocytes |
| Fluids | Saliva - Bile - Intestinal juice - Gastric juice - Pancreatic juice |
| Processes | Swallowing - Vomiting - Peristalsis (Interstitial cell of Cajal) - Migrating motor complex - Borborygmus - Gastrocolic reflex - Segmentation contractions - Defecation |
Glycoproteins: 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 |
he:פקטור פנימי nl:Intrinsic factorfi:Sisäinen tekijä
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
