Erythrocytopoieses proceeds normally in the bone marrow and involves a lot of biochemical and morphological alterations of different shapes - from a directed stem cell through proerythroblast, basophilic erythroblast, polychromatophilic erythroblast, acidophilic erythroblast, reticulocyte to the mature erythrocyte.
In the bone marrow, the developing stages of erythrocytes last 4 to 5 days. On average, 16 erythrocytes develop from the early proerythroblast during that time.

Normal erythrocytopoiesis needs:

• adequate number of stem cells of the erythrocytic lineage;
• presence of growth factors; and
• endocrine regulation.

The bone marrow is able to create about 900 billions of erythrocytes per hour, so replacing the same number of erythrocytes that simultaneously degrade themselves by using mononuclear macrophages of the histomonocytic system. This process holds the population of 25 x 1012 of circulating erythrocytes with a total of 750 g of hemoglobin.
If the life span of erythrocytes decreases to one-tenth of their normal life, or they are lost from the circulation by one-tenth of the total amount, the maximum production capacity of the bone marrow is inadequate. This results in the deficit of erythrocytes in circulation, i.e., anemia. Pathologic changes may cause excessive erythrocyte production, which results in increased the total amount of these cells in the circulation, i.e., erythrocytosis.