Elastic fibers in arterial walls enable them to:

• A. Stretch with systole and recoil with diastole
• B. Contract during systole
• C. Expand during diastole only
• D. Become rigid during exercise

Answer: (A)

Elastic fibers in arterial walls provide resilience that lets the vessels stretch as blood is ejected during systole and then snap back, or recoil, during diastole. This stretch-and-recoil stores some of the heart’s energy and releases it to keep blood flowing smoothly between heartbeats. That windkessel effect smooths the pulsatile pressure from the heartbeat, helping maintain steady perfusion to tissues and reducing large swings in systolic pressure.

The other ideas don’t fit: arteries don’t actively contract to push blood forward (that task is primarily performed by the heart and, to a lesser extent, by smooth muscle tone in the vessel walls). They don’t expand only during diastole—their elasticity allows expansion during systole and recoil during diastole. And they don’t become rigid during exercise; elasticity helps accommodate increased flow and pressure rather than becoming rigid.