Figure 2 shows a cross section of an artery and of a vein. Describe two ways that the structure of an artery is different from the structure of a vein.

Arteries and veins have different structures related to their functions. 1. **Thicker, more muscular and elastic walls:** Arteries carry blood away from the heart under high pressure. They need thick, strong, and elastic walls to withstand this pressure and to stretch and recoil with each heartbeat, which helps maintain blood flow. Veins have much thinner walls as the blood pressure is lower. 2. **Narrower lumen:** Arteries have a relatively narrow lumen (the internal channel) compared to their wall thickness, which helps maintain high blood pressure. Veins have a wider lumen to reduce resistance to blood flow, as the pressure is much lower. 3. **Valves:** Although not shown in this cross-section, veins contain valves to prevent the backflow of blood, which is necessary due to the low pressure. Arteries do not have valves as the high pressure from the heart prevents backflow.