XII.F: Proplatelet Egress

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XII.F.001

Proplatelet Egress. Murine marrow. Megakaryocyte shown in very close apposition to the sinus endothelium. Lumen (L). (Scanning electron micrograph)

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XII.F.002

Proplatelet Egress. Murine marrow. Megakaryocytes (asterisks) shown in very close apposition to the sinus endothelium. Note proplatelets from megakaryocyte on the left of sinus penetrating sinus endothelium and entering lumen (L). (Scanning electron micrograph)

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XII.F.003

Proplatelet Egress. Murine marrow. Megakaryocyte cytoplasm containing demarcation membranes and future platelet granules shown in very close apposition to the sinus endothelium. Note cytoplasmic probe penetrating sinus endothelium (Arrow). Lumen(L). Asterisk marks endothelial cell junction. (Transmission electron micrograph)

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XII.F.004

Proplatelet Egress. Murine marrow. Megakaryocyte cytoplasm shown in very close apposition to the sinus endothelium. Note cytoplasmic probe penetrating sinus endothelium. (Arrow) Lumen (L) (Transmission electron micrograph)

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XII.F.005

Proplatelet Egress. Murine marrow. Megakaryocyte cytoplasm traversing sinus endothelium and entering lumen (L). Further separation into single platelets occurs in marrow circulation, prior to entry into systemic circulation. This megakaryocyte has a marginal zone at its periphery, which is devoid of organelles (arrow). Some megakaryocytes have this marginal zone and many do not. (Transmission electron micrograph)

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XII.F.006

Proplatelet Egress. Murine marrow. (A) Megakaryocyte cytoplasm traversing sinus endothelium and entering lumen (L). (B) Megakaryocyte cytoplasm traversing sinus endothelium and entering lumen (L). An eosinophil and reticulocyte are in the sinus lumen. Further separation of proplatelets into single platelets usually occurs in the marrow circulation prior to entry into systemic circulation. (Transmission electron micrograph)

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XII.F.007

Proplatelet Egress. Murine marrow. Megakaryocyte cytoplasm traversing sinus endothelium and entering lumen (L). The marginal band of peripheral cytoplasm devoid of organelles is present in some megakaryocytes. The marginal band is rich in filaments, including actin. Further separation of proplatelet into single platelets usually occurs in marrow circulation prior to entry into systemic circulation. (Transmission electron micrograph)

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XII.F.008

Proplatelet Egress. Murine marrow. Megakaryocyte cytoplasm traversing sinus endothelium and entering lumen (L). Further separation into single platelets usually occurs in marrow circulation prior to entry into systemic circulation. (Transmission electron micrograph)