Which statement about lumen diameter is correct?

Which statement about lumen diameter is correct?

• A. The lumen diameter is fixed and cannot change.
• B. Lumen diameter can change as smooth muscle contracts or relaxes.
• C. Only arteries have lumens.
• D. Lumens contain bones.

Answer: (B)

The diameter of a blood vessel’s lumen can change because its wall contains smooth muscle that can contract or relax. When smooth muscle contracts, the lumen narrow s (vasoconstriction), which reduces blood flow and raises resistance. When the muscle relaxes, the lumen widens (vasodilation), increasing blood flow and lowering resistance. This dynamic ability lets the body regulate how much blood reaches different tissues and helps maintain blood pressure. That makes the statement about lumen diameter changing with smooth muscle activity the best fit. The idea that the lumen is fixed ignores the real, ongoing ability of vessels to constrict or dilate. It’s not true that only arteries have lumens—veins and capillaries also have interior spaces through which blood flows. And lumens do not contain bones; bones are separate structures altogether.

The diameter of a blood vessel’s lumen can change because its wall contains smooth muscle that can contract or relax. When smooth muscle contracts, the lumen narrow s (vasoconstriction), which reduces blood flow and raises resistance. When the muscle relaxes, the lumen widens (vasodilation), increasing blood flow and lowering resistance. This dynamic ability lets the body regulate how much blood reaches different tissues and helps maintain blood pressure.

That makes the statement about lumen diameter changing with smooth muscle activity the best fit. The idea that the lumen is fixed ignores the real, ongoing ability of vessels to constrict or dilate. It’s not true that only arteries have lumens—veins and capillaries also have interior spaces through which blood flows. And lumens do not contain bones; bones are separate structures altogether.