The absorption of iron

I N the following review I shall confine my relnarks to ( 1) a summary of observations that are accepted presently with little con-troversv, (2) an examination of the classic concept of ‘ ‘mucosal block ” and (3) a discussion of recent studies that relate to the mechanism, rate and control of iron absorption. I shall focus attention on iron absorption in man but, when necessary, I will cite studies in other species to fill in gaps in our knowledge. There is general agreement that absorption of iron can occur at any level of the gastro-intestinal tract from the stomach distally. ’ However, absorption is greatest in the duo-denum and progressively less in a descending gradient.6 Divalent ferrous iron is absorbed better than the trivalent form.”#{176} Uptake of iron by the intestinal mucosal cell is uni-(lirectional; there is practically no excretion of iron into the ‘ ‘. 12 Iron from the mucosal cell emmters the bloodstream directly rather than via the lymphatics.9 ” Under normal conditions the body’s iron content remains constant at levels of 4 to 3 gm., and absorption balances excretion of .5 to 1.5 mg. per day.’4 Iron absorption increases in patients with iron deficiency anemia or pyridoxine deficiency, in the last months of pregnancy, some stages of hemochromatosis and under a variety of conditions which produce increased erythro-poiesis.’” ” A reduction in iron absorption occurs less predictably in patients with som