Chronobiology and Chronopharmacology of the Haemopoietic System

The bone marrow, an extremely complex tissue comprising approximately 4.5% of an adult’s body weight (a mass comparable to the liver) (Nathan 1988), is found in the ends of flat bones (sternum, ribs, skull, vertebrae and innominates) and contains the haemopoietic stem cells, which give rise to the many developing functional blood cell lineages within the marrow spaces. After birth, the bone marrow is the production site for all types of blood cells, which are released through vascular channels into the peripheral blood according to the needs of the body, mediated through different feedback mechanisms. Haemopoiesis is the multi-phase process of cell proliferation and gradual maturation, until the end stage is reached with a population of mature cells that can exert their specialized functions, but are no longer capable of cell proliferation (Laerum et al. 1989).