Thrombocytopoiesis (Megakaryocytopoiesis)
Megakaryocytes are huge bone marrow cells, 50 – 70 microns, with a highly polymorphic nucleus. They are the source of platelets (thrombocytes), cell fragments that aid in blood clotting. The polymorphic nucleus results from a unique process called endomitosis, whereby chromosome replication occurs but neither nuclear nor cytoplasmic division follows. Thus megakaryocyte nuclei are polyploid, containing from 8 to 16 sets of chromosomes. 1000x all
Megakaryoblast >
The megakaryoblast is the first recognizable cell in the megakaryocyte lineage. The nucleus is round or indented and the basophilic cytoplasm is largely free of specific granules. The nucleus undergoes endomitosis, eventually forming a multilobed, highly polymorphic, polyploid nucleus.
Maturing megakaryocytes >
Successive endomitoses, accompanied by the development of complex cytoplasmic structures, result in the formation of mature megakaryocytes. Unlike mature cells in the erythropoietic (red blood cells) and leukopoietic (white blood cells) lineages, megakaryocytes remain in the bone marrow releasing as many as 8000 platelets into the marrow sinusoids for dispersal in the blood stream.
- Platelets
Successive endomitoses, accompanied by the development of complex cytoplasmic structures, result in the formation of mature megakaryocytes. Unlike mature cells in the erythropoietic (red blood cells) and leukopoietic (white blood cells) lineages, megakaryocytes remain in the bone marrow releasing as many as 8000 platelets into the marrow sinusoids for dispersal in the blood stream.
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