Erythrocyte Differentiation.(Various Stages of Stem Cells)

http://en.wikipedia.org/wiki/Erythropoiesis

In the process of red blood cell maturation, a cell undergoes a series of differentiations. The following stages of development all occur within the bone marrow:

1. A Hemocytoblast, a multipotent hematopoietic stem cell, becomes
2. a common myeloid progenitor or a multipotent stem cell, and then
3. a unipotent stem cell, then
4. a pronormoblast, also commonly called an proerythroblast or a rubriblast.
5. This becomes a basophilic or early normoblast, also commonly called an erythroblast, then
6. a polychromatophilic or intermediate normoblast, then
7. an orthochromatic or late normoblast. At this stage the nucleus is expelled before the cell becomes
8. a reticulocyte.

The cell is released from the bone marrow after Stage 7, and so in newly circulating red blood cells there are about 1% reticulocytes. After one to two days, these ultimately become "erythrocytes" or mature red blood cells.

These stages correspond to specific appearances of the cell when stained with Wright's stain and examined by light microscopy, and correspond to other biochemical changes.

In the process of maturation, a basophilic pronormoblast is converted from a cell with a large nucleus and a volume of 900 fL to an enucleated disc with a volume of 95 fL. By the reticulocyte stage, the cell has extruded its nucleus, but is still capable of producing hemoglobin.

Essential for the maturation of red blood cells are Vitamin B₁₂ (cobalamin) and Vitamin B₉ (Folic acid). Lack of either causes maturation failure in the process of erythropoiesis, which manifests clinically as reticulocytopenia, an abnormally low amount of reticulocytes.