Physiology · Blood
Erythropoiesis: stages, regulation and factors affecting it
- Erythropoiesis is the process of formation of red blood cells; after birth it occurs solely in the bone marrow (medullary erythropoiesis).
Sites of Erythropoiesis
- After birth, bone marrow is the sole site:
- Till adolescence, all bones participate.
- After age 20 to 30 years, limited to sternum, ribs, vertebrae, skull, and pelvic and pectoral girdles.
- In intrauterine life, erythropoiesis occurs in three sequential stages:
- Mesoblastic: yolk sac, intravascular.
- Hepatic: liver/spleen, from 5th week.
- Medullary: bone marrow, from 5th month.
- Medullary erythropoiesis is slow in the second trimester but becomes more effective toward the end of the third trimester.
- Extramedullary erythropoiesis in postnatal life is always considered abnormal.
Stages of Erythropoiesis