Question

Discuss the absorption and transport of iron into the protoporphyrin ring during erythropoiesis.

Answer 1

First of all it is important to understand that iron absorption is a long and complex process in our body. Dietry iron is found in our food in organic forms. Ferrous iron (Fe²⁺) in heme which is better in absorption then ferric iron (Fe3⁺) compounds. Firstly organic ferric compounds will be broken in the gut to organic ferric iron but heme will not be broken as it can be easily absorbed. Iron is absorbed through microvilli of the enterocytes of the deudenum. Ferrous iron (Fe²⁺) in heme will enter to the interior side through a receptor called HCP-1. Once the ferric iron reaches the cell surface it will change into ferrous state due to the presence of ferric reductases enzymes before entering into the cell through a protein called DMT-1. Iron coming out to plasma is controlled through Ferroportin. It will be oxidized into ferric iron. Transferrin which is a protein carrier will carry iron. Transferrin which is used for iron transport can carry upto two atoms of trivalent iron. In bone marrow, stem cell undergoes cell divisions forming erythroid progenitors which is a erythroid colony forming unit. Till the reach, the first recognizable erythroid precursor in the bone marrow is pronormoblast. Transferrin will go to the RBC precursor where it will bind itself to the transferrin receptor on its surface. When this complex will enter into the cell, iron is left there and transferrin and its receptor returns back. Extra ferric iron (Fe3⁺) will be provided from the ferritin in the RBC. Ferritin is a iron-protein complex which is used for iron storage and releases iron as per the body needs. This ferric iron (Fe3⁺) will be further reduced to ferous iron. Protoporphyrin will be formed in the mitochondria known as the power house of the cell. Each protoporphyrin molecules contains four pyrroles rings. Iron will go to mitochondria to unite with protoporphyrin and forms heme molecule which go the the cytosol which is the aqueous component of the cytoplasm of a cell. Then globins will be formed from amino acids in the cell. There are two type of globin called alpha and beta. Both the globins will attach with the heme to form hemoglobin molecule which contains four unit with two alpha and two beta globins and four similar heme molecules.