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
First response to decreased blood volume 
Select and explain. 
A. Increased hea rate, B. Tachypnea, C. Hypotension, D. Disorientation
A: Increased hea rate
Answer: A: Increased hea rate 
Explanation: 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