All the following occur in hemostasis except (PGI June 2008)
Correct Answer: Dissolution of clot by plasmin
Description: Ans. C (Dissolution of clot by plasmin) "Plasmin cleaves fibrin at distinct sites of the fibrin molecule leading to the generation of characteristic fibrin fragments during the process of fibrinolysis"- Harrison 17th/365Normal Hemostasis# The Main steps of haemostatic mechanis are:Vasospasm of blood vessels'3Platelet plug formation1Fibrin clot formationFig.: Coagulation is initiated by tissue factor (TF) exposure, which, with factor (F) Vila, activates FiX and FX which in turn, with FVIH and FV as cofactors, respectively, results in thrombin formation and subsequent conversion of fibrinogen to fibrin. Thrombin activates FXl, FVIH, and FV, amplifying the coagulation signal. Once the TF/FVUa/FXa complex is formed, tissue factor pathway inhibitor (TFPI) inhibits the TF/FVlla pathway, making coagulation dependent on the amplification loop through FIXfFVlll. Coagulation requires calcium (not shown) and takes place on phospholipid surfaces, usually the activated platelet membraneAlso Remember:The major components of the hemostatic system, which function in concert, are (1) platelets and other formed elements of blood, such as monocytes and red cells; (2) plasma proteins (the coagulation and fibrinolytic factors and inhibitors); and (3) the vessel wall itself.# On vascular injury, platelets adhere to the site of injury, usually the denuded vascular intimal surfacePlatelet adhesion'-' results in subsequent platelet activation and aggregationDuring platelet aggregation (platelet-platelet interaction), additional platelets are recruited from the circulation to the site of vascular injury, leading to the formation of an occlusive platelet thrombus.# The platelet plug is anchored and stabilized by the developing fibrin mesh. # The immediate trigger for coagulation is vascular damage that exposes blood to TF that is constitutively expressed on the surfaces of subendothelial cellular components of the vessel wall
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