This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood: Hemostasis and Blood Coagulation, Subject name: Physiology
[{'content': 'Ion which is needed for conversion of Prothrombin to thrombin is? \nSelect and explain. \nA. Sodium, B. Potassium, C. Magnesium, D. Calcium', 'role': 'user'}, {'content': "Answer: D \nExplanation: ANSWER: (D) CalciumREF: Guyton's physiology 22nd edition page 459Conversion of Prothrombin to ThrombinFirst, prothrombin activator is formed as a result of rupture of a blood vessel or as a result of damage to special substances in the blood. Second, the Prothrombin activator, in the presence of sufficient amounts of ionic Ca++t causes conversion of Prothrombin to thrombin (Figure 36- 2). Third, the thrombin causes polymerization of fibrinogen molecules into fibrin fibers within another 10 to 15 seconds.", 'role': 'assistant'}]