<unk>  is the process by which red blood cells (erythrocytes) are produced. In human adults, this usually occurs within the bone marrow. In the early fetus,<unk>  takes place in the mesodermal cells of the yolk sac. By the third or fourth month,<unk>  moves to the spleen and liver. In humans with certain diseases and in some animals,<unk>  also occurs outside the bone marrow, within the spleen or liver. This is termed extramedullary<unk> .
The tibia and femur cease to be important sites of hematopoiesis by about age 25; the vertebrae, sternum, pelvis and ribs continue to produce red blood cells throughout life.
Erythropoiesis
Neoplasm
Inflammation
Bone marrow suppression
Neuropathy
Neurulation
Carcinogenesis
Leukostasis