AP BIOLOGY

Detailed explanation-1: -Compared to arteries, veins are thin-walled vessels with large and irregular lumens (see Figure 6). Figure 6. Many veins have valves to prevent back flow of blood, whereas venules do not. In terms of scale, the diameter of a venule is measured in micrometers compared to millimeters for veins.

Detailed explanation-2: -Veins. A vein is a blood vessel that conducts blood toward the heart. Compared to arteries, veins are thin-walled vessels with large and irregular lumens (see Figure 18.2.

Detailed explanation-3: -Arteries have thick, muscular walls and relatively small lumens. They also possess a membrane of elastic fibers, that helps them to stretch and withstand the pressure of the constant pumping by the heart without being damaged. Unlike veins, arteries do not possess valves.

Detailed explanation-4: -Veins carry unoxygenated blood towards the heart, away from tissues at low pressure so the lumen is large. Blood moves more slower and often against gravity so valves and a larger lumen ensure it is still transported efficiently.