This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'The first step in the initiation of primary hemostasis for clot formation? \nSelect and explain. \nA. Fibrin deposition, B. Vasoconstriction, C. Platelet adhesion, D. Thrombosis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Steps in hemostasis at the site of injury\ni) Vasoconstriction • Immediate hemostasis following injury is achieved by brief arteriolar vasoconstriction.\nIt is due to the reflex neurogenic mechanism. This effect is transient. \nii) Primary hemostasis • It is achieved by formation of the primary hemostatic plug (platelet plug).\nFollowing an injury to endothelium, the thrombogenic subendothelial matrix is exposed and allows the platelets to adhere with collagen of ECM.\nThese platelets are activated and recruit other platelets by their secretions.\niii) Secondary hemostasis\n• Activation of coagulation (clotting) system leads to the formation of the secondary hemostatic plug (definitive plug or fibrin clot) which is composed of fibrin, platelets, RBCs, and thrombin.\niv) Dissolution of clot • Activation of the fibrinolytic system results in dissolution of the clot.', 'role': 'assistant'}]