This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiac Output, Subject name: Physiology
When a person moves from a supine position to a standing position, which of the following compensatory changes occurs? 
Select and explain. 
A. Decreased hea rate, B. Increased contractility, C. Decreased total peripheral resistance (TPR), D. Decreased cardiac output
B: Increased contractility
Answer: B: Increased contractility 
Explanation: When a person moves to a standing position, blood pools in the leg veins, causing decreased venous return to the hea, decreased cardiac output, and decreased aerial pressure. The baroreceptors detect the decrease in aerial pressure, and the vasomotor center is activated to increase sympathetic outflow and decrease parasympathetic outflow. There is an increase in hea rate (resulting in a decreased PR interval), contractility, and total peripheral resistance (TPR). Because both hea rate and contractility are increased, cardiac output will increase toward normal