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chapter 29

Metabolism of Iron and Heme

FIGURE 29-2

Intestinal absorption of dietary iron. Ferrous iron is absorbed by the duodenal villus tip enterocytes mediated by divalent

metal transporter-1

(DMT 1). Iron transport mediated by DMT 1

of the apical surface and the basolateral transporter at

the basolateral surface are coupled to ferric reductase and ferroxidase that change the iron oxidation state, respectively.

The degree of iron entry is determined by the level of DMT1 and its level of expression is programmed in the crypt

cells. The programming of the crypt cells is coupled to the body iron stores via transferrin-mediated and HFE

protein-modulated iron transport. [Modified and reprinted with permission from B. R. Bacon, L. W. Powell,

P. C. Adams, et al. Molecular medicine and hemochromatosis: at the cross roads.

G a stro en tero lo g y

116,

193 (1999).]

loss for a 70-kg man is 0.5-1 mg/d, an amount equal to

that normally absorbed from the diet. During growth, men-

struation, and pregnancy, the requirement reaches about

2-2.5 mg/d. Recommended daily iron intake for various

groups is shown in Appendix IV.

The principal loss of iron in nonpregnant women dur-

ing the reproducing years is through menstruation. In one

study, the mean menstrual blood loss was 43.4 ± 2.3 mL.

Since each milliliter of blood from a normal woman con-

tains about 0.5 mg of iron, the amount lost every 27 days is