Question

How are arteries and veins structurally adapted to their functions?

Answer 1

They each withstand a different amount of pressure - each are adapted to this condition

Explanation:

Arteries transport oxygenated blood from the left ventricle (largest, most muscular chamber of the heart) are thicker walled in order to withstand greater amounts of blood pressure. Veins are thinner walled as they transport deoxygenated blood back to the heart under far less pressure and as such don't require as thick of walls.
Veins are also laden with valves to prevent the backflow of blood (typically due to gravity) and maintain directionality within the double-looped circulatory system.

I Found a pretty good explaination here if you want to learn more.