Arteriolar blood pressure increases in response to all but which of the following?

• A. Increased blood volume
• B. Increased sympathetic tone
• C. Vasoconstriction
• D. Falling blood volume

Answer: (D)

Arteriolar pressure rises when the system’s driving forces for blood flow are increased, either by boosting how much blood is returning to the heart or by constricting the vessels to raise resistance. When blood volume grows, venous return and preload go up, which increases stroke volume and cardiac output, pushing arterial pressure higher. Greater sympathetic tone does two things at once: it makes the heart pump harder and faster, and it constricts arterioles, both of which raise arterial pressure by increasing cardiac output and systemic vascular resistance. Vasoconstriction itself heightens resistance in the arterioles, directly elevating the pressure downstream. In contrast, a fall in blood volume reduces venous return and preload, lowers cardiac output, and thus lowers arterial pressure. So the arteriolar pressure would increase with more volume, with sympathetic-driven activity, and with vasoconstriction, but it would not increase with falling blood volume.