Hematopoiesis: Red Blood Cell and Bone Marrow

HEMATOPOIESIS

The formation and development of the cells of the blood.

It is a continuous regulated process of blood cell production that includes cell renewal, proliferation, differentiation and maturation.

It is the process by which immature precursor cells develop into mature blood cells. The currently accepted theory on how this process works is called the monophyletic theory which simply means that a single type of stem cell gives rise to all the mature blood cells in the body. This stem cell is called the pluripotential (pluripotent) stem cell.

SITES OF HEMATOPOIESIS
|Age |Site |
|Embryo |Yolk sac then liver |
|3rd to 7th month |Spleen |
|4th and 5th months |Marrow cavity – esp. granulocytes and platelets |
|7th month |Marrow cavity – erythrocytes |
|Birth |Mostly bone marrow; spleen and liver when needed |
|Birth to maturity |Number of active sites in bone marrow decreases but retain |
| |ability for hematopoiesis |
|Adult |Bone marrow of skull, ribs, sternum, vertebral column, pelvis, |
| |proximal ends of femurs |

In fetal development, hematopoiesis occurs in