Platelets are the smallest type of blood cells, which are only fragments of bone marrow megakaryocyte cytoplasm and are biconvex discs, approximately 3 μm in diameter. The development of megakaryocytes and production of platelets are unique processes. Megakaryocyte maturation involves nuclear duplication without cell division, resulting in giant cells. Cytoplasmic organelles are organized into domains representing nascent platelets, demarcated by a network of invaginated plasma membranes. Within the marrow, megakaryocytes are localized next to the sinusoidal walls and this facilitates the exit of large segments of cytoplasm into the circulation. The fragmentation of megakaryocyte cytoplasm into individual platelets then results from the shear forces of circulating blood . Thrombopoietin (TPO) is the dominant hormone controlling megakaryocyte development, but many cytokines and hormones take part, including interleukins 3, 6, and 11 .