Tag Archives: Megakaryocyte

Osteoclast Morphology

18 Jun Osteoclast - Oil IMG_6456

This was a 32 year old patient whose bone marrow aspiration was done for a suspected diagnosis of a leukaemia. The aspirate yielded a scanty amount of pauciparticulate marrow. Blasts were seen. What was remarkable was the presence of many osteoclasts along a clot on the smear. One of the osteoclasts is seen here in low power. Note the size relative to the erythrocyte. The same osteoclast shown in the previous image unser 100X. Another osteoclast in the same smear. The multiple nuclei. Each nucleus is 1.5-2X adjoining erythrocytes. This gives an idea of the size of the cells. A megakaryocytic though a large cell like an osteoclast normally has a single multi-lobed nucleus

Osteoclast are multinucleate bone resorbing cells derived from the haemopoietic stem cell. An osteoclast is about 30-100μ in size and has multiple discrete oval nuclei. They have azurophilic granules. The megakaryocyte though a large cell, unlike an osteoclast, normally has a single multi-lobed nucleus. Osteoclasts are truly multinucleate. The azurophilic granules of osteoclasts are coarser.

Megakaryocyte Morphology

22 Dec 122211_0219_Megakaryocy1.jpg

Megakaryocytes, the precursors of platelets, are the largest cells in the bone marrow. They are the earliest morphologically recognizable cells of the megakaryocyte-platelet lineage. Megakaryocytes arise from the stem cell via the megakaryocytic erythroid progenitors (MEPs), burst forming units – megakaryocytic (BFU-MK), colony forming unit megakaryocytic (CFU-MK) and the megakaryoblast. Megakaryoblasts are 10-20μm in size. They share morphological features with blasts of other lineages. Megakaryocytes from patients with acute megakaryocytic leukaemia may show pseudobleb formation. CD41 and CD61 mark the megakaryocytic lineage.

Megakaryocytes are large cells (50-100μm) with a multilobed nucleus. They have been classified into three groups according to maturity. The boundaries between these groups are arbitrary and blurred. The most immature megakaryocytes have a strong basophilic granule free cytoplasm and high nuclear/cytoplasmic ratio. With intermediate maturation basophilia decreases, azurophilic granules appear cytoplasm and nuclear lobulation increases. The most mature megakaryocytes have a large amount of weakly basophilic cytoplasm with an abundance of azurophilic granules and polylobulated nucleus. Megakaryocytes, unlike other cells in the bone marrow, are polyploid (4N-32N). The 4N megakaryocytes are exclusively immature and 32N are dominantly mature. Polyploidy occurs because of endomitosis (DNA duplication without mitosis). Endomitosis is essential for normal platelet production but the mechanism of endomitosis in poorly understood.

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