Arteries have a thick layer of smooth muscle and elastic fibres in their walls, whereas veins have only a small amount of each. Explain how the wall structure of arteries is suited to the high-pressure blood flow they carry.

1. The thick elastic fibres in the tunica media allow the artery wall to stretch when the heart ejects blood, preventing rupture under high pressure.
2. When the pressure falls, the elastic fibres recoil, acting like a spring to keep the blood pressure continuous between heartbeats.
3. The thick smooth‑muscle layer can contract or relax, thereby controlling the arterial lumen diameter and influencing resistance.
4. A small lumen, together with the elastic recoil, helps maintain the high pressure required for systemic circulation.