Erythropoiesis

Erythropoiesis is the process of erythrocyte - red blood cell - production. All erythrocytes are derived from the division and differentiation of a common stem cell precursor.

The site of erythropoiesis varies with developmental stage:

• embryo (2.5mm): blood islands of yolk sac
• embryo (5-7mm): liver and spleen
• fetus (20 weeks): bone marrow takes over
• prepuberty: medullary marrow of all bones
• postpuberty: fatty yellow marrow replaces red marrow from the peripheries of bones
• adult: erythropoiesis only in ribs, sternum, vertebrae, shoulder girdle, proximal femur and tibia

If the adult is chronically stressed, the sites of erythropoiesis may re-extend to involve both liver and spleen.

There are a number of factors controlling erythropoiesis. Erythropoietin is the key hormone.