Why are artery walls typically thicker than in veins?

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Arterial walls are thick because they must withstand the high pressure generated by the heart as it pumps blood into the systemic circulation. The thick wall, especially the tunica media full of smooth muscle and elastic fibers, allows arteries to expand with each beat and then recoil, helping to maintain a stable pressure and push blood forward efficiently. Veins, by contrast, operate under much lower pressure, so their walls are thinner and their lumens larger to accommodate more blood volume; they also rely on valves and surrounding muscles to help return blood to the heart. While proximity to the heart correlates with exposure to higher pressure, the key reason for thicker arterial walls is the need to endure that high pressure rather than their location alone. Large lumens and valves are features of veins, not arteries.