This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'First response to decreased blood volume \nSelect and explain. \nA. Increased hea rate, B. Tachypnea, C. Hypotension, D. Disorientation', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Baroreceptor reflex is an immediate compensatory mechanism in shock. There is stimulation of aerial baroreceptors and so sympathetic output is increased leading to vasoconstriction and reflex tachycardia. Ref: Textbook of medical physiology by N Geetha, 2nd edition, page no. 184', 'role': 'assistant'}]