Erythropoiesis is the formation of the red blood cells a process which takes place in the bone marrow. All blood cells are formed in the bone marrow, a soft, highly cellular tissue that fills the internal cavities of the long bones. It takes place in 8 stages where the first seven steps takes place within the bone marrow and after the 7th step the red blood cell is released into the blood stream as reticulocyte which then matures to erythrocyte after 1-2 days.