Compared to veins, arteries typically have thicker walls.

• A. Arteries have thicker walls.
• B. Veins have thicker walls.
• C. Arteries carry blood toward the heart.
• D. Veins carry blood away from the heart.

Answer: (A)

Arteries have thicker walls because they must withstand the high pressure produced when the heart pumps blood into them. The middle layer is rich in smooth muscle and elastic tissue, allowing arteries to expand a bit and then recoil, which helps push blood along and maintain pressure between heartbeats. Veins, on the other hand, carry blood at much lower pressure, so their walls are thinner and they have a larger lumen, often with valves to prevent backflow. The statement about arteries having thicker walls is the best description of this structural difference, since the other choices describe the direction of blood flow rather than wall thickness.