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Erythropoiesis Factors Affection Growth Physiology

Presentation Notes on Factors Effecting Growth & Maturation of Red Blood Cells (RBC) for Medical Biology Students in word/. ppt / .pdf Format


FACTORS NECESSARY FOR ERYTHROPOIESIS

Various substances are necessary for the development and maturation of erythrocytes. These factors are classi­fied into 3 categories, namely:

a.   General factors
b.   Maturation factors

GENERAL FACTORS
Erythropoiesis is influenced by a variety of general factors namely,
1.   Erythropoietin
2.   Thyroxine
3.   Hemopoietic growth factors
4.   Colony stimulating factors and
5.   Vitamins

1. Erythropoietin
The most important general factor for erythropoiesis is the hormone erythropoietin secreted by kidneys. It is also called hemopoietin or erythrocyte stimulating factor.

Chemistry
Erythropoietin is a glycoprotein.

Source of Secretion
Erythropoietin is secreted by peritubular capillaries of kidneys.

Stimulant for Secretion
Hypoxia is the stimulant for the secretion of erythropoietin.

Actions of Erythropoietin
Erythropoietin causes formation and release of new red blood cells into circulation. After secretion, it takes 4 to 5 days to show the action. The hormone promotes the following processes:
1.   Production of proerythroblasts from the stem cells in CFU-E of the bone marrow.
2.   Development of proerythroblasts into matured red blood cells through the normoblastic stages—early, intermediate and late normoblasts and reticulocyte.
3.   Release of matured erythrocytes into blood through the capillary membrane from bone marrow. Even some reticulocytes (immature erythrocytes) are released along with matured red blood cells.

2. Thyroxine
In addition to erythropoietin, thyroxine also forms an important general factor for erythropoiesis. Thyroxine accelerates the process of erythropoiesis at many levels. In hyperthyroidism, polycythemia is common.

3. Hemopoietic Growth Factors
Hemopoietic growth factors or growth inducers are the interleukins and stem cell factor (steel factor). Generally these factors induce the proliferation of pluripotent stem cells.
Interleukins (IL) are glycoproteins which belong to the cytokines family. The interleukins involved in erythropoie­sis are interleukin-3 (IL-3), interleukin-6 (IL-6) and inter-leukin-11 (IL-11). IL-3 is secreted by T lymphocyte. IL-6 is secreted by T lymphocytes, endothelial cells and macrophages. IL-11 is secreted by osteoblasts.

4. Colony Stimulating Factors
The colony stimulating factors (CSF) cause the forma­tion of colony forming blastocytes. There are three types of colony stimulating factors.
i. Granulocyte CSF (G-CSF) secreted by monocytes and endothelial cells.
ii. Granulocyte-Monocyte CSF (GM-CSF) secreted by monocytes, endothelial cells and T lymphocytes,
iii. Monocyte CSF (M-CSF) secreted by monocytes and endothelial cells.

5. Vitamins
Some vitamins are also necessary for the process of erythropoiesis. The deficiency of these vitamins cause anemia associated with other disorders. The vitamins, which are necessary for erythropoiesis are:
1.   Vitamin B: Its deficiency causes anemia and pellagra.
2.   Vitamin C: Its deficiency causes anemia and scurvy.
3.  Vitamin D: Its deficiency causes anemia and rickets.

MATURATION FACTORS
Vitamin B12, intrinsic factor and folic acid are necessary for the maturation of red blood cells.

1.  Vitamin B12 (Cyanocobalamin)
This is essential for maturation of erythrocytes. The deficiency of vitamin B12 causes pernicious anemia. So, Vitamin B12 is called antipernicious factor.

Source of Vitamin B12
Vitamin B12 is called extrinsic factor because it is obtained mostly from diet. Its absorption from the intestine requires the presence of intrinsic factor of Castle. Vitamin B12 is stored in the liver and muscle (mostly liver), necessary, it is transported to the bone marrow to promote f maturation of red blood cells. It is also produced in the  large intestine by the intestinal flora.

Action of Vitamin B12
Vitamin B12 is essential for synthesis of DNA. Its deficiency leads to failure in maturation of the cell and reduction in the cell division. Also, the cells are larger with fragile and weak cell membrane.

2.   Intrinsic Factor of Castle
This is produced in gastric mucosa. This is essential for the absorption of vitamin B12 from intestine into the blood. In the absence of intrinsic factor, vitamin B12 is not absorbed. This happens in severe gastritis, ulcers and gastrectomy. The deficiency of intrinsic factor also causes pernicious anemia since the vitamin B12is not absorbed The extrinsic and intrinsic factors are together called Hematinic principle.

3.   Folic Acid
This is also essential for maturation. This is required for the synthesis of DNA. In the absence of folic acid, the synthesis of DNA is reduced causing failure of maturation. This leads to anemia in which, the cells are larger and appear in megaloblastic (proerythroblastic) stage And the anemia due to the folic acid deficiency is called megaloblastic anemia.

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