Intrinsic factor is a glycoprotein produced and secreted by the parietal cells of the stomach. The stimulus for production can be either vagal, gastrin or histamine signals.
It forms a complex with dietary vitamin B12. The ileum has specific receptors on its enterocytes for the complex. In the presence of calcium ions and a low pH, vitamin B12 is then taken up by the cell and intrinsic factor is rereleased into the gut.
Hence, a deficiency of intrinsic factor can lead to vitamin B12 deficiency. Intrinsic factor levels may be reduced by pernicious anaemia or any cause of decreased surface area or activity of gastric mucosa.
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