Mature Red Blood Cell
Size:
6.7 to 7.7 μ in diameter.
Cytoplasm:
Pink in color.
The
mature red blood cell is a nonnucleated, round, biconcave cell.
Erythropoiesis:
The main function of the red blood cell is to transport oxygen to the tissues.
Production of red blood cells (erythropoiesis) is initiated by a hormone
produced by the kidney called erythropoietin.
When a person’s hemoglobin level is below normal, his tissues will not receive
an adequate supply of oxygen, and this will stimulate the kidneys to increase
their production of erythropoietin. The increased erythropoietin will then
stimulate the stem cells of the bone marrow to differentiate into the
pronormoblast, and there will be an increased number of red blood cells
produced. As the red cells are maturing they undergo several cellular
divisions. Once the orthochromic normoblast stage is reached, however, the cell
is no longer capable of mitosis but will continue to mature in the bone marrow.
The reticulocyte remains in the marrow for approximately two days and is then
released into the peripheral blood. The
red cells of the circulating blood have a lifespan of approximately 120 days, ±20
days.
Hemoglobin structure
and synthesis: Hemoglobin is made up of the protein, globin, and heme. In
normal adult hemoglobin, the globin portion of each molecule consists of four
polypeptide chains: two α and two β chains. These chains, in turn, are composed
of 141 and 146 amino acids (arranged in a specific sequence), respectively.
Each chain is bent and coiled. The heme group is composed of four pyrrole rings
connected by methene bridges. In the center of this structure is an atom of
iron to which oxygen is attached, when the iron is in the ferrous state (Feˉˉ).
One heme molecule will be attached to each of the α and β
chains. Two α and two β chains come together to form a tetramer. The single
hemoglobin molecule, therefore, consists of two α chains, two β chains, and
four heme groups (thus, four atom of iron). Mature red blood cells are incapable
of hemoglobin synthesis. The production of heme and globin takes place
independently of each other, beginning in the polychromatic normoblast, and
ending in the reticulocyte stage.
Author: Dayyal Anand
Author: Dayyal Anand
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