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: Physiology
[{'content': 'Extrinsic system (blood coagulation) is triggered by the release of: September 2008 \nSelect and explain. \nA. Prothrombin, B. Thromboplastin, C. Fibrinogen, D. Thrombin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B: Thromboplastin Factor X can be activated by reactions in either of two systems, an intrinsic and an extrinsic system. The extrinsic system is triggered by the release of tissue thromboplastin, a protein-phospholipid mixture that activates factor VII. The tissue thromboplastin and factor VII activate factors IX and X. In the presence of PL, Ca2+, and factor V, activated factor X catalyzes the conversion of prothrombin to thrombin. The extrinsic pathway is inhibited by a tissue factor pathway inhibitor that forms a quaternary structure with TPL, factor VIIa, and factor Xa.', 'role': 'assistant'}]