Chapter 8 The lymphorecticular system and bone marrow/Fig 8.26.jpg

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Simplified diagram of normal haemopoiesis. The pluripotent stem cell in the marrow gives rise to a number of progenitor cells that in turn proliferate and differentiate to produce all the cellular constituents of blood, including lymphoid cells. This process is controlled by various growth factors, produced by a range of cells including lymphocytes and endothelial cells, the secretion of which is partially dependent on environmental factors; for example hypoxia induces erythropoietin secretion, resulting in increased red cell production. The marrow stroma provides the appropriate environment for stem cells to grow and proliferate. The stem cell, which is capable of producing approximately 106 mature blood cells, is also capable of self renewal.