What effect do short-term responses to hemorrhage have on cardiac output and vessel diameter?

• A. Increase cardiac output and vasodilation
• B. Decrease cardiac output and vasoconstriction
• C. Increase cardiac output and vasoconstriction
• D. Decrease cardiac output and vasodilation

Answer: (C)

When blood is lost quickly, the body ramps up the sympathetic nervous system through baroreceptors. This increases heart rate and the force of contraction, while also constricting most systemic blood vessels. The venous system tightens as well, pushing blood from the reservoir back toward the heart, which helps maintain preload and stroke volume. The combined effect is to raise cardiac output and produce vasoconstriction to compensate for the fall in blood volume and arterial pressure. That’s why the best answer is increased cardiac output and vasoconstriction.