platelet(redirected from Hayem, Georges)
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platelet:see blood clottingblood clotting,
process by which the blood coagulates to form solid masses, or clots. In minor injuries, small oval bodies called platelets, or thrombocytes, tend to collect and form plugs in blood vessel openings.
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(also thrombocyte), a formed element found in the blood of vertebrate animals and man that plays an important role in blood coagulation. The platelets of vertebrate animals (except mammals) are small ovoid cells with a solid nucleus and weakly basophilic cytoplasm. In mammals, including man, platelets are anuclear bodies 2–5 µ in diameter. The platelets normally number about 250,000–350,000 per cubic mm of blood. They have granules containing serotonin and substances involved in blood coagulation, as well as mitochondria, microtubules, glycogen granules, and sometimes ribosomes. In mammals, platelets originate in the blood-forming organs when fragments of the cytoplasm of megakaryocytes separate from the megakaryocytes. The life-span of the platelets of mammals, including man, is about five to nine days.