The page below is a sample from the LabCE course Bone Marrow Aspiration: Normal Hematopoiesis and Basic Interpretive Procedures. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Megakaryocyte: Mature

The mature megakaryocyte is the largest cell found in the bone marrow. It can easily reach more than ten times the size of the other cells and usually has as much, if not more, cytoplasmic volume than it has nucleus.

Once nuclear/DNA replication found in the early megakaryocyte has halted, the amount of cytoplasm will begin to increase until the megakaryocyte reaches its maximum mature size. As platelet granule production increases, the cytoplasm color will shift from basophilic to the grainy pink texture and light lavender color we are familiar with in peripheral platelets. When the cytoplasm has matured enough to produce platelet granules, the process of shedding platelets can begin. This can occur either as an ongoing continuous process or as a single complete release leaving a naked megakaryocyte nucleus.

Notice the extremely large sizes of the megakaryocytes in the images to the right. The megakaryocytes tend to be found in the heart of the bone marrow fragments rather than loosely scattered throughout the smear. Observe the proportion of nucleus to cytoplasm. Notice the foamy, shaggy, irregular cytoplasmic border of the single megakaryocyte that is circled in the bottom image. This megakaryocyte is in the process of releasing platelets and small clusters of platelets can be seen in its vicinity.