Haematopoiesis<unk>  (from Greek 'erythro' meaning "red" and 'poiesis' "to make") is the process which produces red blood cells (erythrocytes), which is the development from erythropoietic stem cell for mature red blood cell. It is stimulated by decreased O2 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<unk>  in the hemopoietic tissues, ultimately producing red blood cells (erythrocytes). In postnatal birds and mammals (including humans), this usually occurs within the red 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 liver. After seven months,<unk>  occurs in the bone marrow. Increased level of physical activity can cause an increase in<unk> . However, 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 bone marrow of essentially all the bones produces red blood cells until a person is around five years old. The tibia and femur cease to be important sites of hematopoiesis by about age 25; the vertebrae, sternum, pelvis and ribs, and cranial bones continue to produce red blood cells throughout life. Up to the age of 20 years, RBCs are produced from red bone marrow of all the bones (long bones and all the flat bones). After the age of 20 years, RBCs are produced from membranous bones such as vertebrae, the sternum, ribs, scapulas, and the iliac bones. After 20 years of age, the shaft of the long bones becomes yellow bone marrow because of fat deposition and loses the erythropoietic function.
Erythropoiesis
Cytotoxicity
Vasculogenesis
Digestion
Muscle hypertrophy
Phototoxicity
Neoplasm
Vasoactivity