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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.

Megakaryoblast (MK-I)

FIGURE 4–2A Megakaryoblast, MK-I—bone marrow (×1000).

FIGURE 4–2B Megakaryoblast, schematic.

Size:

10-24 μm

Nucleus:

Round

Nucleoli:

2-6

Chromatin:

Homogeneous, loosely organized

Cytoplasm: basophilic

Granules:

Absent by Wright stain

N/C RATIO:

3:1

Reference interval:

Bone marrow:

20% of megakaryocyte precursors in bone marrow

Peripheral blood:

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).

Promegakaryocyte (MK-II)

FIGURE 4–4A Promegakaryocyte, MK-II—bone marrow (×1000).

FIGURE 4–4B Promegakaryocyte, schematic.

Size:

15-40 μm

Nucleus:

Indented

Nucleoli:

Variable

Chromatin:

Condensed

Cytoplasm:

Basophilic

Granules:

Present

N/C RATIO:

1:2

Reference interval:

Bone marrow:

25% of megakaryocyte precursors in bone marrow

Peripheral blood:

0%

FIGURE 4–5 Megakaryocyte sequence—megakaryocyte (MK-III).

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).

Size:

20-90 μm

Nucleus:

2-32 lobes (8 lobes: most common)

Note:

The size of the cell varies according to number of lobes present.

Cytoplasm:

Blue to pink; abundant

Granules:

Reddish blue; few to abundant

N/C RATIO:

Variable

Reference interval:

Bone marrow:

5-10 per 10× objective (×100 magnification)

1-2 per 50× objective (×500 magnification)

Note:

Megakaryocytes are usually reported as adequate, increased, or decreased and not as a percentage.

FIGURE 4–7 Megakaryocyte sequence—platelets.

Peripheral blood:

0%

Platelet

FIGURE 4–8A Platelet—peripheral blood (×1000).

FIGURE 4–8B Electron micrograph of platelet (×28,750).

Size:

2-4 μm

Nucleus:

NA

Cytoplasm:

Light blue to colorless

Granules:

Red to violet, abundant

N/C RATIO:

NA

Reference interval:

Bone marrow:

NA

Peripheral blood:

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.

[/level-membership-for-hematology-oncology-and-palliative-medicine-category][not-level-membership-for-hematology-oncology-and-palliative-medicine-category]

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.

Megakaryoblast (MK-I)

FIGURE 4–2A Megakaryoblast, MK-I—bone marrow (×1000).

FIGURE 4–2B Megakaryoblast, schematic.

Size:

10-24 μm

Nucleus:

Round

Nucleoli:

2-6

Chromatin:

Homogeneous, loosely organized

Cytoplasm: basophilic

Granules:

Absent by Wright stain

N/C RATIO:

3:1

Reference interval:

Bone marrow:

20% of megakaryocyte precursors in bone marrow

Peripheral blood:

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).

Clinical Hematology Atlas