Iron is an unusual nutrient because the body has a very limited capability to excrete excess iron. The three main factors that affect iron balance are absorption, losses, and the amount in stores. Iron is lost in very small amounts, mostly in blood and cells that are excreted into the intestinal tract.
The amount of iron in the body is largely controlled by varying the absorption rate. This varying absorption rate complicates the calculation of how much iron will be absorbed from a meal. In addition, there are enhancers and inhibitors of iron absorption in many meals. The RDAs for iron have been established to supply enough iron when there is a need for extra iron.
Several special proteins assist the body in absorbing iron from food. In the lining of the intestines is a protein called mucosal ferritin. Mucosal ferritin stores iron in the mucous cells lining the intestines, as seen in Figure 11-4. When the body needs iron, another protein, mucosal transferrin, receives iron bound to the mucosal ferritin and delivers it to the blood. The iron is then received by yet another protein, transferrin, which transports iron to the body in blood plasma. If iron is not needed, the iron in the mucous cells in the intestines is excreted after a few days when the cells are shed. In this way, dietary iron is held for use and released if not needed.
Iron is very efficiently recycled in the body. Red blood cells contain most of the iron in the body. After about four months, the older red blood cells die and the iron is recycled. Iron is transported by transferrin in the plasma. Transferrin receptors are synthesized on cell surfaces when a cell needs iron. Transferrin receptors are also used to prevent free iron from appearing in the blood, which could cause free radical damage.
Figure 11-4 Iron absorption from the intestines into the blood.
Three Forms of Iron
Ferritin is used to store extra iron.
Transferrin transports iron in the blood plasma.
Hemosiderin is a compact storage of iron.
Iron is stored in the form of a protein called ferritin. Ferritin can store and release iron to meet demands. Hemosiderin can also store iron in the body. Hemosiderin is a protein larger than ferritin and it has a higher iron content. The primary storage sites in the body for ferritin and hemosiderin are the liver, the spleen, and the bone marrow. This stored iron is especially important in the last six weeks of pregnancy .
The amount of iron in the body is largely controlled by varying the absorption rate. This varying absorption rate complicates the calculation of how much iron will be absorbed from a meal. In addition, there are enhancers and inhibitors of iron absorption in many meals. The RDAs for iron have been established to supply enough iron when there is a need for extra iron.
Several special proteins assist the body in absorbing iron from food. In the lining of the intestines is a protein called mucosal ferritin. Mucosal ferritin stores iron in the mucous cells lining the intestines, as seen in Figure 11-4. When the body needs iron, another protein, mucosal transferrin, receives iron bound to the mucosal ferritin and delivers it to the blood. The iron is then received by yet another protein, transferrin, which transports iron to the body in blood plasma. If iron is not needed, the iron in the mucous cells in the intestines is excreted after a few days when the cells are shed. In this way, dietary iron is held for use and released if not needed.
Iron is very efficiently recycled in the body. Red blood cells contain most of the iron in the body. After about four months, the older red blood cells die and the iron is recycled. Iron is transported by transferrin in the plasma. Transferrin receptors are synthesized on cell surfaces when a cell needs iron. Transferrin receptors are also used to prevent free iron from appearing in the blood, which could cause free radical damage.
Figure 11-4 Iron absorption from the intestines into the blood.
Three Forms of Iron
Ferritin is used to store extra iron.
Transferrin transports iron in the blood plasma.
Hemosiderin is a compact storage of iron.
Iron is stored in the form of a protein called ferritin. Ferritin can store and release iron to meet demands. Hemosiderin can also store iron in the body. Hemosiderin is a protein larger than ferritin and it has a higher iron content. The primary storage sites in the body for ferritin and hemosiderin are the liver, the spleen, and the bone marrow. This stored iron is especially important in the last six weeks of pregnancy .
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