Process of Erythropoiesis
Erythropoiesis (from Greek ‘erythro’ meaning “red” and ‘poiesis’ meaning “to make”) is the process which produces red blood cells erythrocytes.It is stimulated by decreased O2 in circulation, which is detected by the kidneys, which then secrete the hormone erythropoietin.
Because of the inability of erythrocytes (red blood cells) to divide to replenish their numbers, the old ruptured cells must be replaced by totally new cells. They meet their demise because they don’t have the usual specialized intracellular machinery, which controls cell growth and repair, leading to a short life span of 120 days. In foetus , RBC are formed in the liver , spleen and red blood marrow . After birth ,they are formed only in red bone marrow of sternum ,ribs , vertebrae etc . During the process Erythropoiesis or formation of RBC , stage are there for development , they are :-
- The pronormoblast, or erythroblast, is the earliest stage in erythroid maturation which is a very round cell that is about the same size as a myeloblast.
- Proerythrocyte is the first stage of RBC stage formation there is a large cell having a nucleus.
- The first stage does not have haemoglobin initially.
- It is the latter stages that haemoglobin starts to appear .
2. NORMOBLAST :-
- Normoblast , nucleated normal cell occurring in red marrow as a stage or stages in the development of the red blood cell erythrocyte.
- Normoblast stage is second stage of stage RBC formation .
- In this stage a smaller cell is seen where the size of the nucleus decreases and vanishes with the condensation of the chromatin material and haemoglobin fully start to appear .
3. RETICULOCYTE :
- A reticulocyte count is a blood test that measures how fast red blood cells called reticulocytes are made by the bone marrow and released into the blood.
- Reticulocyte is third stage of Erythropoiesis .
- Reticulocyte develops from normoblast in red bone marrow .
- Reticulocyte is stage before full maturity is reached.
- Reticulocyte contains haemoglobin and reticulum in the cytoplasm .
- This is the last stage of Erythropoiesis .
- In this stage RBC is fully developed ,so RBC is also called ERYTHROCYTE .
- It does not contain reticulum but contain adequate haemoglobin.
REGULATION OF ERYTHROPOIESIS
- Low oxygen level in the body .(Reduced oxygen – carrying capacity of the blood )
- Kidney secretes a hormone ERYTHROPOIETIN .
- Erythropoietin stimulates enhanced erythropoiesis in the bone marrow .
- More RBC are produced in the bone marrow .
- This results in the increase in the RBC count
(increased oxygen -carrying capacity of the blood )
- Normal oxygen level of the body is maintained .
This increase in erythropoietic activity elevates the number of circulating RBCs, thereby raising the O2 carrying capacity of the blood and restoring the delivery of O2 to the body tissues to normal. Once the O2 level in the tissues of the kidneys is brought back to normal, erythropoietin secretion is turned down until it is needed again. This is an example of a negative feedback mechanism.