Erythropoiesis Hematology Review 293
PERIOD SITE(S) COMMENTS
1–2 mo of gestation Yolk sac & aorta-gonads- Primitive erythroblasts. Embryonic hemoglobin (Gower I, Gower II,
mesonephros (AGM) region Portland).
3–6 mo of gestation Liver, spleen Liver is primary site.
7 mo of gestation—age 4 yr Bone marrow All marrow is active.
Adult Bone marrow Only active sites are pelvis, vertebrae, ribs, sternum, skull. Shafts of long
bones filled with fat. Fatty marrow may be reactivated to compensate
for anemia. Liver & spleen may be reactivated (extramedullary
hematopoiesis) if bone marrow fails to keep up with demand.