The Biological Role of Iron and Other Metals

Dietary factors other than the type of the iron salt used in the diet also influence iron absorption. Rats on corn diets, high-methionine diets, or ethionine-sup-plemented diets absorb more iron than can be effectively used. 

Possibly one decisive factor in iron absorption is the use of the metal by the erythropoietic tissue. Condi- 

Ferric hydroxide Organic chelates Iron porphyrin 

A new hypothetical mechanism for the control of iron absorption from the intestinal mucosa has been proposed. It is based on two observations (1) the inverse relationship between iron content in the intestinal mucosa and the absorption of iron (2) radioau-tographic studies following injections of labeled iron, which indicate that the iron concentrates in the newly formed cell of the intestinal crypt. In the presence of large iron stores, the iron content of the crypt cell remains unchanged during the entire life of the cell. But if iron is depleted, the iron content of the crypt cell decreases. Thus, as the newly formed crypt cell matures and moves toward the villi, it can absorb new iron. Iron metabolism is summarized in Fig. 6-2. 

In aqueous solutions, metal ions can hold a specific number of water molecules (usually 4-6). The tendency of a cation to become hydrated depends upon its size and charge. The tendency for hydration is least when the radius is greatest and the charge smallest. If other molecules or ions are also present in the solution containing the cation, they may displace the molecules of water involved in the hydration of the cation. For example, a cation Fe may combine with 4 chloride ions to yield Fe CI4 or Fe may combine with 6 cyanide molecules to yield FeCng. The combination of cation with several other ions or molecules 

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