Explain Iron Balance and Regulation of Iron Absorption?

The body has three unique mechanisms for maintaining iron balance. The first is the continuous reutilization of iron from catabolized erythrocytes in the body. When an erythrocyte dies after about 120 days, it is usually degraded by the macrophages of the reticular endothelium. The iron is released and delivered to transferrin in the plasma, which brings the iron back to red blood cell precursors in the bone marrow or to other cells in different tissues. Uptake and distribution of iron in the body is regulated by the synthesis of transferrin receptors on the cell surface. This system for internal iron transpoi-t not only controls the rate of flow of iron to different tissues according to their needs, but also effectively prevents the appearance of free iron and the formation of free radicals in the circulation.

The re-utilization of iron is a highly significant process. As mentioned earlier, the red blood cells (erythrocytes) contain two thirds of the total body iron. If 1/120^th of this is to be degraded daily, (note: life span of erythrocytes is 120 days) it results in the release of about 20 mg of iron daily within the body. Almost all of this is re-utilized for the synthesis of new haelnoglobin and erythrocytes. Only an extremely small proportion i.e., about 1 mg is lost from the body to be replaced by dietary iron. The amount of iron released from erythrocytes and re-utilized for new haemoglobin is termed as iron turnover in the body. The second mechanism involves access to the specific storage protein, ferritin. This protein stores iron in periods of relatively low need and releases it to meet excessive iron demands. This iron reservoir is especially important in the third trimester of pregnancy. The third mechanism involves the regulation of absorption of iron from the intestines; decreasing body iron stores trigger increased iron absorption and increasing iron stores trigger decreased iron absorption. Iron absorption decreases until equilibrium is established between absorption and requirement.