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MEGAKARYOCYTE AND PLATELET PRODUCTION

The earliest small progenitor cells of the megakaryocytic line are not easily differentiated from myeloblasts. They may be identified by electron microscopic or immunologic techniques. Megakaryoblasts undergo nuclear and cytoplasmic maturation from progenitor cells (Fig. 4-18). The megakaryocyte matures through endomitotic synchronous nuclear replications, which enlarge the cytoplasmic volume as the number of nuclei increases in multiples of two. These polyploid cells contain the equivalent of 4, 8, 16, or 32 sets of chromosomes. At a variable stage of development, usually at the 4N, 8N, or 16N stage, further nuclear replication and cell growth cease (Figs. 4-19 and 4-20), the cytoplasm becomes granular, and platelets are produced. Platelets appear as granular basophilic forms with a diameter of 1 to 3 μm (Figs. 4-21 and 4-22). The volume of platelets diminishes as they mature and age in the circulation.

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