Platelet

A small, nucleus-free fragment shed by bone-marrow megakaryocytes that circulates in blood and helps stop bleeding by forming plugs and supporting clot formation.

Primary hemostasis: The formation of a platelet plug at a site of blood-vessel injury. Platelet adhesion and aggregation create the initial seal before a fibrin clot forms.
Megakaryocyte: A large bone-marrow cell that produces platelets by shedding fragments of its cytoplasm. Platelets originate as pieces of this specialized precursor cell.
Complete blood count: A blood test that measures the numbers and characteristics of major blood-cell types. Its platelet count is the routine measure used to detect unusually low or high numbers.
Bernard–Soulier syndrome: A rare inherited bleeding disorder caused by defects in the platelet GPIb-IX-V receptor complex. Defective receptor function prevents normal platelet attachment to von Willebrand factor.
Coagulation: The sequence of reactions that generates fibrin to stabilize a blood clot. Platelet surfaces help assemble coagulation reactions, and fibrin reinforces the platelet plug.
Platelet adhesion: The attachment of platelets to exposed vessel-wall structures at an injury site. Adhesion is the first step that anchors circulating platelets to damaged vessels.
Thrombopoietin: A hormone-like protein that regulates megakaryocyte development and platelet production. It drives the marrow pathway that replenishes circulating platelets.
Thrombocytopenia: An abnormally low platelet count in the blood. Too few platelets can impair plug formation and increase bleeding risk.
Glanzmann thrombasthenia: A rare inherited bleeding disorder caused by deficient or defective platelet integrin αIIbβ3. Without functional αIIbβ3, platelets cannot aggregate normally through fibrinogen bridges.
Thrombosis: The formation of a blood clot within a blood vessel or the heart. Platelet-driven clot formation can obstruct blood flow when it occurs inappropriately.

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