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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 ...
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 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
The protein encoded by the c-mpl gene, CD110, is a 635 amino acid transmembrane domain, with two extracellular cytokine receptor domains and two intracellular cytokine receptor box motifs . TPO-R deficient mice were severely thrombocytopenic, emphasizing the important role of CD110 and thrombopoietin in megakaryocyte and platelet formation.
The GPIb-IX-V complex is a profuse membrane receptor complex originating in megakaryocytes and exclusively functional on the surface of platelets. [1] It primarily functions to mediate the first critical step in platelet adhesion, by facilitating binding to von Willebrand factor (VWF) on damaged sub-endothelium under conditions of high fluid shear stress.
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.
Factor V is produced by megakaryocytes, which produce platelets and platelet-derived factor V, and hepatocytes, which produce plasma-derived factor V. [9] The molecule circulates in plasma as a single-chain molecule with a plasma half-life of 12–36 hours. [10] Factor V is able to bind to activated platelets and is activated by thrombin.