What is Erythropoiesis ?
Erythropoiesis :- Erythropoiesis is , production Development and Maturation of cellular elements of blood ( Erytho = red , poiesis = synthesis)
Site of Blood Cells Poiesis:-
| Normal site’s | Sites for poiesis |
| 1. Fetus : less than 2 months | Yolk sac |
| 2 . From 2 to 7 months | Liver and spleen |
| 3 . After 3 months | Bone marrow |
| 4 . Full term infant | Bone marrow |
| 5 . Children and the adults | Bone marrow |
In normal health only mature cells are seen in the peripheral blood. Development of blood cells takes place 3 stages :-
- Multiplication of precursor cell .
- Structural and functional maturation and
- Release into the peripheral circulation .
The term erythropoiesis mean the generation of erythrocytes.upto the 3rd month of intrauterine life erythropoiesis occurs in the mesoderm of yolk sac. Between the 3rd month and the 5th month of intrauterine life, erythropoiesis occurs in the liver and spleen. This stage is called the Hepatic stage of erythropoiesis. From the 5th month red bone marrow begins to produce erythrocytes . This phase is called Myeloid phase .
Stages of Development:-
The development of mature erythrocyte is through several stages of division and differentiation. There are controversies regarding the details but following details represent the consensus thinking –
- A pluripotent stem cell is the most primitive cell which gives rise to Myeloid as well as lymphocytic series cells .
- The pluripotent stem cell then gives rise to committed stem cells.one type of committed stem cell produces RBCs , neutrophils , eosinophils , monocytes, and platelets ( cells of the Myeloid series ) . The other type of commited stem cell produces the lymphocytes .
- cells committed to produce the Myeloid series, further differentiate and from progenitor cells there are distinctly separate progenitor cells for RBC, granulocytes, monocytes and platelets. Progenitor cells are generally called colony forming unit ( CFU ) cells.
- The first progenitor cell for RBC is called burst forming unit erythrocyte ( BFUE ) . The BFUE undergoes further differentiation and produces colony forming unit erythrocyte ( CFUE ) .
- From the progenitor CFUE , the pronormoblast develops . It is the first morphology recognizable precursor of RBC .
- From pronormoblast early normablast ( large basophilic normoblast ) develops , which in turn , gives rise to intermediate normoblast ( or poltchromatophilic normoblast ) . From intermediate normoblast late normoblast ( or orthochromatic normoblast ) develops .
- From late normoblast develops the reticulocyte the reticulocyte matures for one or two days in bone marrow and then enters the peripheral blood . The reticulocyte give rise to the matured red blood cells.
Note :- As the cell matures , the nuculeus becomes smaller and smaller and the cytoplasm becomes more and more abundant. Hemoglobin appears from the intermediate normoblast stage it increases gradually and fully fills up the cell as the cell matures completely . At the stage of reticulocyte some RNA persists ( which is not present in a matured RBC ) . It can be stained by brilliant cresylblue . In conditions where erythropoiesis is vigorously stimulates reticulocyte count in the peripheral blood increases .
Factors Influencing Erythropoiesis
- Hematopoietic growth factors and interleukins contribute to contribute to control erythropoiesis. They regulate the proliferation and differentiation of hematopoietic precursor cells efacilitate the function of mature erythrocytes.
- Granulocytes / macrophages colony stimulating factor ( GM – CSF ) is a panmyeloid growth factor which stimulates erythroid , granulocyte , monocyte , megakarocyte , and eosinophil progenitors. This results in primary increase of neutrophils monocytes, eosinophils and also in the activation of phagocytic functions.
- Granulocytes colony forming factor ( G – CSF ) stimulates granulocyte production and functional activation .
- BPA : A material, burst promoting activity (BPA) probably produced by lymphocytes and monocytes is responsible for the proliferation of BFUE .
- Erythropoietin : The juxta glomerular apparatus (JGA) of the kidney produces a sbstance called erythrogenin (renal erythropoietic factor (REF) . It acts on a plasma protein called erythropoietin phen and erythropoietin phen is converted into erythropoietin . It is chemically a glycoprotein. Erythropoietin is the active substance for erythropoiesis .
- Vitamins : Vitamins B12 (extrinsic factor ) and folic acid play influencing role in erythropoiesis . Vitamin B6 and vitamin C also have some contributory roles ( Refer chapter 22 , P652 ” chemistry of vitamins) .
- Orher factors required for Erythropoiesis are amino acids , iron , vitamin B6 , cobalt , zinc , copper , androgens , thyroxine , vitamin C and vitamin E ( all factors required in normal quantities ) .
- Erythropoiesis is diminished if there is exposure of the bone to X- ray and during treatment by methotrexate , the anticancer drug .
- The intensity of erythropoiesis can be judged by counting the percentage of reticulocytes in peripheral blood .
- Hypoxia is the stimulus for erythropoietin sacretion . The hypoxia is detected by the kidneys and then the JGA produces the REF which leads to the formation of erythropoietin .
- Where hypoxia is severe ( e.g. advanced emphysema , severe hemorrhage , high altitude ) erythropoietin production is high .
- Erythropoietin production is depressed in advanced cases of chronic nephritis and repeated blood transfusion also depress erythropoietin production .
- Erythropoietin also causes increase in the rate of hemoglobin synthesis and facilities the process of Maturation of reticulocytes .
- Other factors which stimulate Erythropoietin production are ACTH and thyroxine .
Precursors of Erythropoiesis (RBC)
| cell | Approximate cell diameter | Nucleus | Cytoplasm |
| Proeryrhroblast | 15 – 20 micrometre | Big and strongly basophilic | very scanty, basophilic. Does not contain hemoglobin |
| Early narmoblast ( basophilic narmoblast ) | 13 – 17 micrometre | Big nucleus ( but smaller than proertthro last) , basophilic | scanty , basophilic and does not contain hemoglobin |
| Polychromatic narmoblast | 11 – 15 micrometre | Nucules smaller than basophilic normoblast | Cytoplasm appears poltchromatophilic due to the appearance of hemoglobin |
| Orthochormatic narmoblast | 8 – 10 micrometre | very small nuculeus and pink cytoplasm | Large eosinophilc cytoplasm. Hemoglobin is present in fair amount |
| Reticulocyte | 7.5 – 8 micrometre | Nucules absent | Hemoglobin is present in large quantity with little RNA |
| Matured Erythrocyte | 7.5 – 7.2 micrometre | Nucules absent | Hemoglobin is present in large proportion |
What is erythrocytes?
what is erythrocytes ?
Erythrocytes is a circular biconcave cell without a nuculeus . It has a diameter of about 7.5 – 7.2 micrometer and thickness of 2.5 – 2 micrometer , central pallear 1.5 – 1 micrometer , it’s Scarface area 120 micrometre and valume 80 – 90 micrometre . .it cantains hemoglobin and is the heaviest of all the formed elements of of all the formed elements of blood . It’s 90 – 120 days life span in circulation .
what are erythrocytes normal value ?
What are erythrocytes normal value.
male :- 4.5 – 6 million/Cumm
female :- 4.0 – 4.5 million/ Cumm