IRON METABOLISM AND IMPORTANCE OF IRON

IRON METABOLISM

IMPORTANCE OF IRON

Iron is an essential mineral and an important component of proteins, involved in oxygen transport. So, humanbody needs iron for oxygen transport. Iron is important for the formation of hemoglobin and myoglobin. Iron is also necessary for the formation of other substances like cytochrome, cytochrome oxidase, peroxidase and catalase.

NORMAL VALUE AND DISTRIBUTION OF IRON IN THE BODY

Total quantity of iron in the body is about 4 g. Ap proximate distribution of iron in the body is as follows:

In the hemoglobin : 65% to 68%

In the muscle as myoglobin : 4%

As intracellular oxidative heme compound : 1%

In the plasma as transferrin : 0.1%

Stored in the reticuloendothelial system : 25% to 30%

DIETARY IRON

Dietary iron is available in two forms called heme and nonheme.

Heme Iron

Heme iron is present in fish, meat and chicken. Iron in these sources is found in the form of heme. Heme iron is absorbed easily from intestine.

Non-heme Iron

Iron in the form of nonheme is available in vegetables, grains and cereals. Nonheme

iron is not absorbed easily as heme iron. Cereals, flours and products of grains which are enriched or fortified (strengthened) with iron become good dietary sources of nonheme iron, particularly for children and women.

ABSORPTION OF IRON

Iron is absorbed mainly from the small intestine. It is absorbed through the intestinal cells (enterocytes)

by pinocytosis and transported into the blood. Bile is essential for the absorption of iron. Iron is present mostly in ferric (Fe3+) form. It is converted into ferrous form (Fe2+) which is absorbed into the blood. Hydrochloric acid from gastric juice makes the ferrous iron soluble so that it could be converted into ferric iron by the enzyme ferric reductase from enterocytes. From enterocytes, ferric iron is transported into blood by a protein called ferroportin. In the blood, ferric iron is converted into ferrous iron and transported.

TRANSPORT OF IRON

Immediately after absorption into blood, iron combines with a β-globulin called apotransferrin (secreted by liver through bile) resulting in the formation of transferrin. And iron is transported in blood in the form of transferrin. Iron combines loosely with globin and can be released easily at any region of the body.

STORAGE OF IRON

Iron is stored in large quantities in reticuloendothelial

When the size of RBC increases (macrocyte), ESR also increases.

FACTORS DECREASING ESR

1. Viscosity of Blood

Viscosity offers more resistance for settling of RBCs. So when the viscosity of blood increases, the ESR

decreases.

2. RBC count

When RBC count increases, the viscosity of blood is increased and ESR decreases. And when the RBC

count decreases, ESR increases cells and liver hepatocytes. In other cells also it is stored in small quantities. In the cytoplasm of the cell, iron is stored as ferritin in large amount. Small quantity of iron

is also stored as hemosiderin.

DAILY LOSS OF IRON

In males, about 1 mg of iron is excreted everyday through  feces. In females, the amount of iron loss is very much high. This is because of the menstruation. One gram of hemoglobin contains 3.34 mg of iron.

Normally, 100 mL of blood contains 15 gm of hemoglobin and about 50 mg of iron (3.34 × 15). So, if 100 mL of blood is lost from the body, there is a loss of about 50 mg of iron. In females, during every menstrual cycle, about 50 mL of blood is lost by which 25 mg of iron is lost. This is why the iron content is always less in females than in males. Iron is lost during hemorrhage and blood donation also. If 450 mL of blood is donated, about 225 mg of iron is lost.

REGULATION OF TOTAL IRON IN THE BODY

Absorption and excretion of iron are maintained almost equally under normal physiological conditions. When the iron storage is saturated in the body, it automatically reduces the further absorption of iron from the gastrointestinal tract by feedback mechanism.

Factors which reduce the absorption of iron:

1. Stoppage of apotransferrin formation in the liver, so that the iron cannot be absorbed from the intestine.

2. Reduction in the release of iron from the transferrin, so that transferrin is completely saturated with iron

and further absorption is prevented.

 

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