Earliest event of vascular trauma is?: (A) Vasoconstriction, (B) Platelet adhesion, (C) Platelet aggregation, (D) Vasodilatation
Answer is A. Ans. (a) Vasoconstriction(Ref: Robbins 9th/pg 661)Endothelial Injury causes vasoconstriction Q (due to endothelin, serotonin) immediately and markedly reduces blood flow to the injured area.