University of Virginia Health System

Mature Megakaryocyte
(Granular Megakaryocyte)

Bone marrow aspirate smear, Wright-Giemsa stain, 1000x

Description:

As the megakaryocyte matures, the cell enlarges in size and may reach 60 μm or more in diameter. The nucleus continues to synthesize DNA and undergoes endomitosis from a diploid state (2C) to a 4C, 8C, 16C and to a polyploid state with up to 128C. During this process, the nucleus does not become multinucleated but does lobate. The cytoplasm also increases markedly in volume, is pale to grey-blue in color, and contains numerous fine azurophilic granules. Irregularly distributed cytoplasmic projections of varying length persist. At maturity, the megakaryocyte extends cytoplasmic projections through the basement membrane between the endothelial cells of the bone marrow sinusoids. Through a process of demarcation and fragmentation of the cytoplasm, platelets are released into the circulation. The stage of nuclear lobation at which platelets are released varies depending on the demand for platelet production. Under normal circumstances, platelets are released between the 8C and 16C stage. Naked or bare megakaryocyte nuclei also are seen and are though to represent the end stage after complete fragmentation of the membrane to form platelets.

A phenomenon referred to as emperipolesis is not infrequently observed in megakaryocytes in normal bone marrow aspirates. The term refers to the presence of one cell inside another (engulfment). The engulfed cell may exit unharmed; in effect, it is the transit of one cell into and out of the cytoplasm of another cell without being degraded by the engulfing cell. Cells representing all hematopoietic lineages and stages of maturation may be engulfed.

For all publication requests, please complete the image permission form and we will respond to your request shortly.