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| __NOTOC__ | | __NOTOC__ |
| {{Vitamin B12 deficiency}}
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| {{CMG}}
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| === Common Causes ===
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| Vitamin B 12 deficiency may be caused by:
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| === Decrease intake ===
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| * Strict vegan diet more than 3 years .
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| * Breast fed infants of pure vegan may also develop deficiency .
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| * Malnutrition most likely happen in elderly patients.
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| === Malabsorption ===
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| * Decrease intrinsic factor due autoimmune destruction of parietal cell
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| * Decrease Gastric acid production due to proton pump inhibitor and histamine 2 receptor antagonists
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| * Gastric by pass surgery because intrinsic factor is produce by parietal cell of stomach
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| * Tapeworm (Diphyllobothrium latum ) ingested from contaminated fish , tapeworm saps nutrients
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| * Crohn's disease
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| === Increased requirement ===
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| * pregnancy
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| == Pathophysiology ==
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| * Dietary Vitamin B12 binds to salivary R factor then the complex arrives at small intestine
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| * In duodenum Vitamin B12 is detach from R- factor by pancreatic proteases
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| * Now free B12 binds to intrinsic factor which is secreted by gastric parietal cell
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| * The intrinsic factor - B12 complex is absorbed in the ileum
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| * Absorbed vitamin B12 is use in metabolic pathways which is important for neurologic and hematologic function if vitamin B12 is deficit regardless of the cause many impairments may occur
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| * Vitamin B12 is a cofactor for the enzyme methionine synthase which convert homocysteine to methionine as a result methyl- THF is converted to THF which is use in synthesis of pyrimidine base of DNA.
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| * In B12 deficiency homocystein accumulate which cause megaloblastic anemia and hypersegmented neutrophils.
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| *
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| ==References== | | ==References== |
| {{Reflist|2}} | | {{Reflist|2}} |
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| | {{WS}} |
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| [[Category:Hematology]] | | [[Category:Hematology]] |
| [[Category:Gastroenterology]] | | [[Category:Gastroenterology]] |
| [[Category:Primary care]]
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| {{WH}}
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| {{WS}}
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