megakaryocyter

Megakaryocytes, known in Danish as megakaryocyter, are large polyploid bone marrow cells that give rise to platelets. They differentiate from hematopoietic stem cells through a lineage involving thrombopoietin (THPO) and the MPL receptor, with intermediate progenitors such as megakaryocyte-erythroid progenitors. They become polyploid by endomitosis, resulting in a single cell with multiple genome copies and extensive cytoplasm. Their cytoplasm extends proplatelets through the endothelial barrier of bone marrow sinusoids, and platelets are released into the bloodstream. Each megakaryocyte can produce thousands of platelets over its lifespan. They express surface markers including CD41 (integrin αIIb), CD42b (GPIbα), and CD61 (GPIIIa) in humans.

Location and development: megakaryocytes reside primarily in the bone marrow; during embryogenesis the liver and spleen contribute hematopoietic cells. After release, platelets circulate for about 7–10 days.

Function: they are the primary source of platelets, essential for hemostasis, clot formation, and wound repair. Their cytoplasmic granules contain a range of coagulation factors, growth factors, and signaling molecules that support vascular maintenance and repair.

Regulation and pathology: thrombopoietin–MPL signaling governs megakaryopoiesis; dysregulation can lead to thrombocytosis or thrombocytopenia. In essential thrombocythemia, megakaryocytes are increased and often dysplastic; in primary myelofibrosis abnormal megakaryocytes secrete transforming growth factor-beta and PDGF, promoting marrow fibrosis. Treatments targeting thrombopoiesis or associated signaling pathways, such as THPO mimetics or JAK inhibitors, are used in myeloproliferative neoplasms.

Overview: megakaryocytes are integral to platelet production and vascular homeostasis, with development and function closely linked to hematologic health and disease.