The red blood cell count is about 4.5 X10¹² red blood, The white blood cell count between between 4-10 X10⁹/L and platelet count is 150-400X10⁹/L. The red blood cells have a life of 120 days and the platelets have lifespan about a week. The lifespan of leucocytes varies but for most is a week to two weeks. The need to renew these cells makes blood the tissue with the highest turnover. Haemopoietic stem cell (HSC) are progenitors of all blood cells.

HSCs what is known as an asymmetric division (see figure below).

1. One of the daughter cells matures into a committed haemopoietic precursor (CHP). This cell over succesive divisions gives rise to cells of the hemopoietic system. Maturation is accompanied by loss of ability to proliferate. The lineages this cells gives rise to include erythrocytes, leucocytes (neutrophils, eosinophils, basophils, monocytes, T and B lymphocytes, natural…