Final answer:
Veins contain numerous valves that prevent backflow of blood and assist its movement toward the heart, facilitated by skeletal muscles.
Step-by-step explanation:
Most veins contain numerous valves to prevent blood from pooling in the limbs and assist blood moving back to the heart. These valves ensure a unidirectional flow of blood and are particularly important in the extremities where the pull of gravity can cause blood to flow backward. Veins take blood back to the heart, while arteries take it away from the heart. Additionally, the action of skeletal muscles helps to move blood through veins.