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Platelets, or thrombocytes, are cell-like structures that stick together to form blood
clots. They join together when exposed to the air, as
in a cut or disturbance of a blood vessel, and they also bind to the
collagen that is exposed when endothelial cell lining a blood vessel are damaged. Platelets are not cells in the conventional sense, but are
fragmented pieces of the cytoplasm of megakaryocytes in the bone marrow, released from the
bone marrow into the bloodstream.
Platelets can be separated from donated blood by using a centrifuge. This is
necessary because platelets do not survive the normal storage used for red
blood cells, so they must be stored separately. People who need additional clotting agents (e.g. hemophiliacs) can benefit
from such donations. A (see-through) bag of platelets is pale orange.
A normal platelet count in a healthy person is between 150 and 400 (x 109/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"
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