ABSTRACT
Haemopoiesis (hematopoiesis if one is reading an American publication)—the word itself a combination of two Greek words ‘haima’ meaning blood and ‘poiesis’ meaning production-is the process by which the many types of blood cell are generated. In the adult mammal, this cell production takes place almost exclusively in the bone marrow although under some pathological conditions haemopoiesis may redevelop in the spleen and even in the liver. In some lower mammals, specifically the mouse, splenic haemopoiesis continues at a low rate throughout life. The products of this process fall into two main categories: the red blood cells (RBC) or erythrocytes whose purpose is to transport oxygen to all the tissues of the body; and the white blood cells (WBC) or leucocytes whose purpose is to protect the body against infection. The scale of production is massive. With a RBC count of 5×1012 per litre and a blood volume of 5 litres, an adult man has 2.5×1013 circulating erythrocytes. Their lifespan is about 115 days, so that the daily turnover-and therefore production-is about 2.2×1011. Neutrophilic granulocytes which constitute 66 per cent of the leucocytes in the blood number about 4.5×109 per litre. Their lifespan, however, is short (less than half a day) indicating an overall WBC production rate of about 1011 per day. This means that the haemopoietic tissue is generating some 3×1011 blood cells of all types per day. At about 109 WBC or 1010 RBC per gramme this represents some 120 g of blood cells (equivalent to a quarter-pound steak, or enough for a black pudding) every day.
