<P> Erythropoiesis ( from Greek ' erythro ' meaning `` red '' and ' poiesis ' meaning `` to make '' ) is the process which produces red blood cells ( erythrocytes ) . It is stimulated by decreased O in circulation , which is detected by the kidneys , which then secrete the hormone erythropoietin . This hormone stimulates proliferation and differentiation of red cell precursors , which activates increased erythropoiesis in the hemopoietic tissues , ultimately producing red blood cells . In postnatal birds and mammals ( including humans ) , this usually occurs within the red bone marrow . In the early fetus , erythropoiesis takes place in the mesodermal cells of the yolk sac . By the third or fourth month , erythropoiesis moves to the liver . After seven months , erythropoiesis occurs in the bone marrow . Increased level of physical activity can cause an increase in erythropoiesis . However , in humans with certain diseases and in some animals , erythropoiesis also occurs outside the bone marrow , within the spleen or liver . This is termed extramedullary erythropoiesis . </P>
<P> Erythropoiesis ( from Greek ' erythro ' meaning `` red '' and ' poiesis ' meaning `` to make '' ) is the process which produces red blood cells ( erythrocytes ) . It is stimulated by decreased O in circulation , which is detected by the kidneys , which then secrete the hormone erythropoietin . This hormone stimulates proliferation and differentiation of red cell precursors , which activates increased erythropoiesis in the hemopoietic tissues , ultimately producing red blood cells . In postnatal birds and mammals ( including humans ) , this usually occurs within the red bone marrow . In the early fetus , erythropoiesis takes place in the mesodermal cells of the yolk sac . By the third or fourth month , erythropoiesis moves to the liver . After seven months , erythropoiesis occurs in the bone marrow . Increased level of physical activity can cause an increase in erythropoiesis . However , in humans with certain diseases and in some animals , erythropoiesis also occurs outside the bone marrow , within the spleen or liver . This is termed extramedullary erythropoiesis . </P>
which substance increases the production of rbc 's
which substance increases the production of rbc 's
erythropoietin
erythropoietin