Hematopoiesis is the process by which the formed elements of the blood are produced. The process is regulated through a series of steps beginning with the pluripotent hematopoietic stem cell. Stem cells are capable of producing red cells, all classes of granulocytes, monocytes, platelets, and the cells of the immune system. The precise molecular mechanism—either intrinsic to the stem cell itself, or through the action of extrinsic factors—by which the stem cell becomes committed to a given lineage is not fully defined. .
