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': 'Following an injury to a blood vessel, immediate haemostasis is achieved by - \nSelect and explain. \nA. Fibrin deposition, B. Platelet adhesion, C. Vasoconstriction, D. Thrombosis', 'role': 'user'}, {'content': "Answer: C \nExplanation: Hemostasis\no Hemostasis is a physiological process whereby bleeding is halted, thus protecting\xa0the integrity' of the\xa0vascular system after tissue injury.\no It is responsible for minimizing blood loss,\no It is commonly referred to as stoppage of bleeding,\no The hemostatic mechanisms have several functions : -\n1. Maintain blood in fluid state while circulating within the vascular system.\n2 Arrest bleeding at the site of injury by formation of hemostatic plug.\n3. Ensure the removal of hemostatic\xa0plug when healing is complete.\no The components of normal hemostasis include: -\n1. Blood vessels (endothelium)\n2. Platelets\n3. Plasma coagulation factors and their inhibitors.\n4. Fibrinolytic system.\no When a blood vessel is injured, several steps occur in hemostasis at the site of injury': -\nA. Vasoconstriction\no After initial injury, there is a brief period arteriolar vasoconstriction, minimizing vessel\xa0diameter and stowing bleeding.\no This is due to reflex neurogenic mechanism and augmented by a potent endothelium derived\xa0vasoconstrictor endothelin.\no However this effect is transient, bleeding would resume if there will no activation of platelet and\xa0coagulation system.\nB. Primary hemostasis\no Endothelial injury exposes highly thrombogenic subendothelial extracellular matrix which allows\xa0the platelets to bind (adhere) with collagen of ECM.\no Binding of platelets activates these cells and platelets release secretory' granules.\no These secretory' products (from secretory granules) recruit additional platelets to form primary\xa0hemostatic (platelet plug).\nC. Secondary hemostasis\no Coagulation\xa0system is activated\xa0and thrombin is generated,\no Thrombin converts fibrinogen to fibrin.\no Ultimately these events form an irreversibly fused mass of platelets, thrombin RBCs and\xa0fibrinogen → Definitive secondary hemostatic plug.\nD. Repair of vessels and dissolution of the clot\no The clot attracts and stimulates the growth of fibroblast and smooth muscle cells within the\xa0vessel wall, and begins the repair process.\no At this stage the fibrinolytic system is also activated, resulting in the dissolution of the clot.", 'role': 'assistant'}]