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Revision as of 13:49, 3 November 2004 by Zeimusu (talk | contribs) (clarification)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)Platelets, or thrombocytes, are the blood cells that are involved in the cellular mechanisms that lead to the formation of blood clots. Like red blood cells they are anuclear and discoid 1.5-3.0u in size. The progenitor cell for platelets is the megakaryocyte. The circulating life of a platelet is 9-10 days. The body has a very limited reserve of platelets and so they can be rapidly depleted. They contain RNA a canalicular system and several different types of granules; lysosomes, dense bodies and alpha granules the contents of which are released upon activation of the platelet. These granule contents play an important role in both hemostasis and in the bodies imflammatory response.
They are activated when brought into contact with collagen exposed when the endothelial blood vessel lining is damaged or with receptors expressed on white blood cells or the endothelial cells of the blood vessels. Once activated they release a number of different coagulation factors and platelet activating factors, this causes the platelets to adhere to each other and to the endothelial cells in the wall of the blood vessel forming in conjucntion with fibrin a clot.
Platelets are separated from donated blood using an apheresis blood seperator, This is necessary because platelets will not survive at the low temperatures used to store red blood cells, so they must be stored separately using porous storage bags that allow in oxygen. People with few platelets or platelets that are dysfunctional may benefit from a platelet transfusion, however patients with autoimmune disorders that affect platelets may not.
A normal platelet count in a healthy person is between 150 and 400 (x 10/L of blood). People can live independently with a count as low as 20. People can live in hospital with a count as low as 5, but spontaneous bleeding gets to be a problem. Platelets can be transfused if a patient's platelet count falls too low. A low platelet count is called thrombocytopenia, having too many platelets is called thrombocytosis.
Thrombocytopenia may be caused by the drugs that stimulate the production of antibodies against platelets. This condition is called "Drug-induced immune thrombocytopenia"
platelet diseases
- disorders of platelet number
- disorders of platelet adhesion
- disorders of platelet aggregation
- disorders of platelet release
- decreased cyclooxygenase activity, induced or congenital
- granule storage pool defects, acquired or congenital
- disorders of platelet coagulant activity
- related disorders
See also:
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| Hematopoiesis |
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| Myeloid tissue |
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