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Platelets are held within these internal membranes within the cytoplasm of megakaryocytes. There are two proposed mechanisms for platelet release. In one scenario, these proto-platelet processes break up explosively to become platelets. [7] It is possible to visualize the spontaneous release of platelets using holotomographic live-cell imaging ...
The megakaryoblast is a platelet precursor that undergoes endomitosis to form megakaryocytes that have 8 to 64 nuclei. Megakaryocytes shed platelets into the bloodstream. β1-tubulin microtubules, which are found in megakaryocytes, facilitate this process of shedding platelets into the bloodstream. [5]
Platelets have no cell nucleus; they are fragments of cytoplasm derived from the megakaryocytes [2] of the bone marrow or lung, [3] which then enter the circulation. Platelets are found only in mammals, whereas in other vertebrates (e.g. birds, amphibians), thrombocytes circulate as intact mononuclear cells. [4]: 3
Thrombopoietin is a glycoprotein hormone produced by the liver and kidney which regulates the production of platelets. It stimulates the production and differentiation of megakaryocytes, the bone marrow cells that bud off large numbers of platelets. [5] Megakaryocytopoiesis is the cellular development process that leads to platelet production.
The promegakaryocytes continue the process of endomitosis, which results in the formation of granular megakaryocytes as the nucleus forms lobes with increased volumes. The megakaryocytes release the platelets into the blood stream. [8] The process of platelet production, beginning with the formation of megakaryoblasts, takes about 7 days.
Platelets, or thrombocytes, are very small, irregularly shaped clear cell fragments, 2–3 μm in diameter, which derive from fragmentation of megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days. Platelets are a natural source of growth factors.
Myeloid cells include monocytes, macrophages, neutrophils, basophils, eosinophils, erythrocytes, and megakaryocytes to platelets. Lymphoid cells include T cells, B cells, natural killer cells, and innate lymphoid cells. The definition of hematopoietic stem cell has developed since they were first discovered in 1961. [5]
Megakaryocyte–erythroid progenitor cells must commit to becoming either platelet-producing megakaryocytes via megakaryopoiesis or erythrocyte-producing erythroblasts via erythropoiesis. [2] [3] Most of the blood cells produced in the bone marrow during hematopoiesis come from megakaryocyte–erythroid progenitor cells. [4]