If blood vessels lose tone or become too relaxed, the blood pressure would

• A. Increase
• B. No change
• C. Fluctuate
• D. Decrease

Answer: (D)

Vascular tone is the tightness of vascular smooth muscle that determines systemic vascular resistance. When vessels relax and dilate, resistance drops. Blood pressure depends on cardiac output times this resistance, so a decrease in resistance leads to lower arterial pressure. Even if the heart beats a bit harder to compensate, the primary effect of relaxed vessels is a fall in blood pressure.