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intrinsic factor n.
A relatively small mucoprotein secreted by the parietal cells of gastric glands and required for adequate absorption of vitamin B12 for production of red blood cells. Also called Castle's intrinsic factor.
a glycoprotein (i.e., a complex compound containing both polysaccharide and protein components) with which vitamin B12 (cyanocobalamin) must combine to be absorbed by the gut. Intrinsic factor is secreted by parietal cells of the gastric glands in the stomach, where it binds with the vitamin. Thus bound, intrinsic factor protects vitamin B12 from digestion as it passes through the gastrointestinal tract and facilitates the vitamin's absorption in the ileum of the small intestine. Vitamin B12 is necessary for red blood cell maturation. A lack of intrinsic factor may result in inadequate absorption of the vitamin and cause pernicious anemia.