PAGE 2 Bone Marrow Function Marrow function is tightly regulated to provide the numbers and types of blood cells needed to meet a wide variety of physiological requirements. The haematopoietic stem cell is a unique cell within the bone marrow responsible for all the formed cellular elements in blood. The stem cell cannot be identified morphologically, but resembles a lymphocyte. The vast majority of stem cells express a surface protein or antigen - CD34 and have receptors for stem cell growth factor which promotes their proliferation. It no longer has the capacity for self renewal and has lost some of its ability for multilineage differentiation.
Differentiation occurs as a result of the acquisition or loss of specific growth factor receptors.
A wide variety of cytokines are also involved in this process. The most primitive identifiable cells in the erythroid line, are relatively resistant to erythropoietin. However, in the presence of other growth factors, they become more responsive to erythropoietin and undergo differentiation. Thus, EPO is a very important differentiating factor. EPO induces RNA synthesis followed by haemoglobin synthesis.