megakaryocyte

Megakaryocytes are large bone marrow cells responsible for the production of blood platelets, essential components of hemostasis. They arise from hematopoietic stem cells through the megakaryocyte-erythroid lineage, with thrombopoietin acting as the main regulator of their development and maturation. In health, megakaryocytes reside in the bone marrow and interact with sinusoidal endothelium to release platelets into the circulation.

Maturation involves endomitosis, a process in which DNA replicates without cell division, yielding polyploid cells that can reach 8–64N. As they mature, megakaryocytes develop a complex cytoplasmic network and a demarcation membrane system. They extend cytoplasmic processes called proplatelets into bone marrow sinusoids, and platelets are formed by fragmentation of the cytoplasm within these processes and released into the bloodstream.

Anatomically, megakaryocytes are among the largest cells in the marrow, typically 30–100 micrometers in diameter, with a multilobed nucleus. They are primarily located near vascular sinusoids, where mechanical forces and thrombotic regulators facilitate platelet release. Platelets produced by megakaryocytes circulate for roughly 7–10 days, performing primary hemostatic functions by forming a platelet plug and supporting clot formation, before being cleared by the spleen and liver.

Clinical relevance includes disorders of megakaryopoiesis and platelet production. Thrombocytopenia can arise from impaired megakaryocyte development or increased platelet destruction, while myeloproliferative neoplasms may feature abnormal megakaryocyte morphology and excessive platelet production, contributing to disease progression.