The main function of blood platelets is to ensure hemostasis and prevent hemorrhages. The 10¹¹ platelets needed daily are produced in a well-orchestrated process. However, this process is not yet fully understood and in vitro platelet production is still inefficient. Platelets are produced in the bone marrow by megakaryocytes, highly specialized precursor cells that extend cytoplasmic projections called proplatelets (PPTs) through the endothelial barrier of sinusoid vessels. In this Cell Science at a Glance article and the accompanying poster we discuss the mechanisms and pathways involved in megakaryopoiesis and platelet formation processes. We especially address the – still underestimated – role of the microenvironment of the bone marrow, and present recent findings on how PPT extension in vivo differs from that in vitro and entails different mechanisms. Finally, we recapitulate old but recently revisited evidence that – although bone marrow does produce megakaryocytes and PPTs – remodeling and the release of bona fide platelets, mainly occur in the downstream microcirculation.

血小板的主要功能是确保止血和防止出血。每天需要的10 ^11个血小板是经过精心策划的过程产生的。但是，此过程尚未完全了解，并且在体外血小板生产仍然效率低下。血小板是由巨核细胞产生的，巨核细胞是高度专门化的前体细胞，其通过正弦血管的内皮屏障扩展被称为前血小板（PPT）的胞质投射。在此《细胞科学概览》文章和随附的海报中，我们讨论了巨核细胞生成和血小板形成过程涉及的机制和途径。我们特别解决了（仍然被低估了）骨髓微环境的作用，并提出了有关体内PPT扩展与体外PPT扩展有何不同的最新发现并需要不同的机制。最后，我们总结了过去但最近重新访问的证据，尽管骨髓确实会产生巨核细胞和PPT，但重塑和真正的血小板释放主要发生在下游微循环中。