1- Haemostatic Mechanism3

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VasoconstrictionImmediate vasoconstriction of the injured vessel and reflexconstriction of adjacent small arteries and arterioles is responsiblefor an initial slowing of blood flow to the area of injury.The reduced blood flow allows activation of platelets andcoagulation factors.The vasoactiveamines and Thromboxane A2 (TXA2) liberated fromplatelets, and the fibrinopeptides liberated during fibrin formation,also have vasoconstrictive activity.
Stabilization of the platelet plug by fibrinDefinitive haemostasis is achieved when fibrin, formed by bloodcoagulation, is added to the platelet mass.Following vascular injury, the formation of extrinsic Xase (VIIa,TF, PL and Ca2+) initiates the coagulation cascade.Platelet aggregation and release reactions accelerate the coagulationprocess by providing abundant membrane phospholipid.The much larger amounts of thrombin generated by the secondaryintrinsic Xase at the injury site converts soluble plasma fibrinogeninto fibrin, potentiates platelet aggregation and secretion and also
Page 1 and 2: The Platelets, BloodCoagulation and
Page 3 and 4: The haemostatic system represents a
Page 5 and 6: Platelets
Page 7 and 8: Megakaryocytes: (a) immature form w
Page 9 and 10: Thrombopoietin (TPO)is the major re
Page 11 and 12: The normal platelet count is approx
Page 14 and 15: ➢The binding site for IIb/IIIa is
Page 16 and 17: ➢During the release reaction, the
Page 18: Von Willebrand factor (VWF)VWF is i
Page 21 and 22: Platelet aggregationThis is charact
Page 23 and 24: 2- Thromboxane A2 (TXA2) is importa
Page 25 and 26: Growth factorPDGF found in the α g
Page 27 and 28: ➢The operation of this (the coagu
Page 29 and 30: The coagulation factors.
Page 31 and 32: InitiationCoagulation is initiated
Page 34 and 35: Endothelial cellsThe endothelial ce
Page 38 and 39: activates factor XI and XIII and co
Page 40 and 41: Coagulation factor inhibitorsIt is
Page 43 and 44: The action of protein C is enhanced

1- Haemostatic Mechanism3

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