Thrombocyte
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Alternatively and usually known as "platelets", these are differentiated fragments of the bone marrow cell known as the megakaryocyte. They are a component of circulating blood.
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Function
- Stop haemorrhage after vascular injury
- Supportive role in inflammatory response in endothelial microenvironment and after injury
Physiology
Their actions are mediated by:
- Release of lipid and (glyco) protein mediators upon activation
- This includes the release of the contents of alpha granules containing protein mediators and dense granules containing serotonin and nucleotides.
- Adhesion to other platelets, collegen, fibrin mesh and damaged cells with contraction mediated by their submembranous filaments of various platelet contractile proteins.
- Aggregate with neutrophils
- Time dependent
- Pre-mRNA splicing
- Translation of mRNA
The roles are more complex than this with for example platelet activation and enzyme systems like platelet eNOS(NOS-3) activity (releasing nitric oxide) being associated with conditions like systemic and pulmonary hypertension, atherosclerosis, and thrombotic diseases with much active research taking place.
Formation (Thrombopoeisis)
- Induction by megakaryocyte specific growth factors, predominantly thrombopoietin (TPO) binding to the c-Mpl receptor and signalling induction,over days. There is megakaryocyte nuclear proliferation to up to 32 nuclei and a change in cytoplasm content with new cytoskeletal proteins, platelet specific granules and membranes.
- A release phase in hours. At this time the megakaryocyte may protrude as many as 10-20 proplatelets, long cytoplasmic extrusions that can branch with the potential to form up to about 1000 platelets from one mature megakaryocyte. The proplatelets elongate at about 0.85 µm/min[1] as the microtubules, which are the main structural component of proplatelets, slide over each other, driven by dynein motors associated with dynactin its regulatory complex. Kinesin motors then carry platelet organelles into the proplatelets using the microtubule bundles as tracks. Only at the ends of proplatelets are formed microtubule coils similar to that observed in mature platelets as a single rolled microtubule approximately 100 µm in length [2].
See Wikipedia:Platelet for the more established details.
References
- ↑ Patel SR, Richardson JL, Schulze H, Kahle E, Galjart N, Drabek K, Shivdasani RA, Hartwig JH, Italiano JE. Differential roles of microtubule assembly and sliding in proplatelet formation by megakaryocytes. Blood. 2005 Dec 15; 106(13):4076-85.(Link to article – subscription may be required.)
- ↑ Italiano JE, Patel-Hett S, Hartwig JH. Mechanics of proplatelet elaboration. Journal of thrombosis and haemostasis : JTH. 2007 Jul; 5 Suppl 1:18-23.(Link to article – subscription may be required.)
