Published on 04/03/2015 by admin
Filed under Hematology, Oncology and Palliative Medicine
Last modified 22/04/2025
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4 Megakaryocyte maturation
Platelets arise from the megakaryocyte. Megakaryocytes are among the largest cells in the body and mature by a unique process called endomitosis. In endomitosis, the nucleus is duplicated but there is no cell division, resulting in a polyploid cell. Megakaryocyte nuclei may have from 2 to 32 lobes and, in unusual cases, may have up to 64 lobes. Megakaryocytes develop copious cytoplasm, which differentiates into platelets. Platelets have several types of granules that can be visualized by electron microscopy. The granules are highly specialized. Refer to a hematology textbook for further discussion.
FIGURE 4–1 Megakaryocyte sequence—megakaryoblast MK-I.
FIGURE 4–2A Megakaryoblast, MK-I—bone marrow (×1000).
FIGURE 4–2B Megakaryoblast, schematic.
10-24 μm
Round
2-6
Homogeneous, loosely organized
Absent by Wright stain
3:1
20% of megakaryocyte precursors in bone marrow
0%
Note:
The megakaryoblast appears similar to the myeloblast and pronormoblast, and identification by morphology alone is not advisable.
FIGURE 4–3 Megakaryocyte sequence—promegakaryocyte (MK-II).
FIGURE 4–4A Promegakaryocyte, MK-II—bone marrow (×1000).
FIGURE 4–4B Promegakaryocyte, schematic.
15-40 μm
Indented
Variable
Condensed
Basophilic
Present
1:2
25% of megakaryocyte precursors in bone marrow
FIGURE 4–5 Megakaryocyte sequence—megakaryocyte (MK-III).
FIGURE 4–6A Megakaryocyte, MK III—bone marrow (×500).
FIGURE 4–6B Megakaryocyte, MK-III, schematic.
FIGURE 4–6C Electron micrograph of megakaryocyte (×16,500).
20-90 μm
2-32 lobes (8 lobes: most common)
The size of the cell varies according to number of lobes present.
Blue to pink; abundant
Reddish blue; few to abundant
5-10 per 10× objective (×100 magnification)
1-2 per 50× objective (×500 magnification)
Megakaryocytes are usually reported as adequate, increased, or decreased and not as a percentage.
FIGURE 4–7 Megakaryocyte sequence—platelets.
FIGURE 4–8A Platelet—peripheral blood (×1000).
FIGURE 4–8B Electron micrograph of platelet (×28,750).
2-4 μm
NA
Light blue to colorless
Red to violet, abundant
7-25 per 100× oil immersion field (×1000 magnification)
FIGURE 4–9 Megakaryocyte sequence with (A) megakaryoblast, (B) promegakaryocyte, (C) megakaryocyte, and (D) platelet.
All photomicrographs are ×1000 original magnification with Wright-Giemsa staining unless stated otherwise.
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