Lichtman M A, Chamberlain J K, Simon W, Santillo P A
Am J Hematol. 1978;4(4):303-12. doi: 10.1002/ajh.2830040402.
Megakaryocytopoiesis occurs in the hematopoietic (extravascular) compartment of marrow. Thus, platelets must traverse the wall of the vascular sinuses of marrow to enter the circulation. We have examined mouse and rat marrow, fixed by rapid immersion so as to maintain anatomical relationships as close to the natural state as possible. Quantitative transmission electron microscopy (TEM) of random transections of femurs established that megakaryocytes reside less than 1 mu from a marrow sinus wall with a probability unlikely to be the result of chance (P less than 0.001). An intimate relationship exists between the megakaryocyte periphery and the abluminal surface of the endothelial lining cell. At the time of platelet release megakaryocyte cytoplasm invaginates and penetrates the endothelial lining cell. The penetrating cytoplasm is detached and enters the marrow circulation. From their dimensions in comparison to circulating platelets, the released cytoplasm represents a packet of platelets that undergoes further fragmentation in the circulation. The parasinusoidal location of megakaryocytes and the process of sinus-wall penetration and platelet delivery was observed by TEM and scanning electron microscopy. These studies provided quantitative support for a specific anatomical arrangement of megakaryocytes in marrow. Moreover, the process of platelet release appears to be a physiological form of metastasis with invasion of vascular walls and vascular spread of cells, that are in this case amitotic.
巨核细胞生成发生在骨髓的造血（血管外）区域。因此，血小板必须穿过骨髓血管窦壁才能进入循环。我们检查了小鼠和大鼠的骨髓，通过快速浸入固定，以尽可能保持接近自然状态的解剖关系。对股骨随机横切面进行的定量透射电子显微镜（TEM）检查确定，巨核细胞位于距离骨髓窦壁不到1微米处，其概率不太可能是偶然结果（P小于0.001）。巨核细胞周边与内皮衬里细胞的腔外表面之间存在密切关系。在血小板释放时，巨核细胞细胞质内陷并穿透内皮衬里细胞。穿透的细胞质分离并进入骨髓循环。与循环血小板相比，从其大小来看，释放的细胞质代表一包血小板，它们在循环中会进一步碎片化。通过TEM和扫描电子显微镜观察到了巨核细胞的窦周位置以及窦壁穿透和血小板递送过程。这些研究为骨髓中巨核细胞的特定解剖排列提供了定量支持。此外，血小板释放过程似乎是一种生理形式的转移，伴有血管壁侵袭和细胞的血管内扩散，在这种情况下细胞是无丝分裂的。
