Erythropoiesis as word erythro-cyte means red blood cells and poiesis means to form. So, the word meaning is formation of new red blood cells.
Erythropoiesis is define as a process through which body will produce new red blood cells.
Where does Erythropoiesis process occur?
Erythropoiesis occurs in the red bone marrow. All the blood cells are formed here only.
For some time, i.e. from embryonic stage to 5 to 6 months of pregnancy, eryhropoieis occurs in the liver and spleen. As bone marrow matures completely on 7th month of pregnancy from that time bone marrow is the only place where the RBC formation takes place, i.e. erythropoiesis occurs.
Who regulate the Erythropoiesis?
Erythropoiesis process is regulated by one hormone called erythropoietin, which is formed 90 percent in kidney and only 10 percent in the liver.
Basically, Kidneys detect blood oxygen level, if it is low then kideny starts forming this erythropoietin. Later, it travels to the bone marrow and stimulate bone marrow erythroid stem cells (responsible for formation of blood cells). Thereafter, it starts increasing the production of RBC.
When RBC number increases, oxygen level get normal. or when body hypoxia (low oxygen level) comes to normal again, this hormone stops from producing resulting in normal erythropoiesis process.
So, main stimulator for the erythropoiesis is the oxygen level in the blood detected by the kidney.
Stages/ Steps of Erythropoiesis
There are 8 stages of cells, to completely form the Red blood cells. This are,
- Hematopoietic Stem Cell
- Myeloid progenitor
- Proerythroblast
- Basophilic erythroblast
- Polychromatophilic erythroblast
- Orthochromatic erythroblast
- Reticulocyte
- Mature Erythrocyte (Red blood cell)
Hematopoietic stem cell, is the first cell of the body, that can be divided into any types of blood cells, as WBC or RBC or Platelets.
Myeloid progenitor is the second stage, it is develop from hematopoietic stem cell. This cell then further develop into RBC. It can also develop into other cells, but 90 percent it turn into the RBC.
Proerythroblast is the first identifiable red blood cells. In this, stage, this cell start producing the hemoglobin.
Next is, Basophilic erythroblast, it is next cell, where hemoglobin synthesis increases, and cell size decreases.
Next, Polychromatophilic erythroblast, in this stage, active cell division process starts. It means the cells are multiply through mitosis to increase the number of RBC. So, this way body produces millions of RBC required for body. In this, stage nucleas becomes smaller and hemoglobin gets accumulated.
Orthochromatic erythroblast (Normoblast), this stage is mark by nucleus is small and eventually loss. Cells are stop dividing in this stage.
Reticulocyte are the final immature RBC, they get released prematurely in the blood. Further they matured in 1 or 2 days. During this time, they release other organelles and fully convert to working RBCs.
Mature Erythrocyte (red blood cell) – This cells are fully mature RBC, without nucleus. Their shape is biconcave. The total time taken to form new RBC is 120 days.