What is the main role of veins in the circulatory system?

Veins play a crucial role in the circulatory system by transporting low-pressure blood back to the heart. After oxygen is delivered to tissues through the arteries, the deoxygenated blood returns from the body's organs and muscles through the veins. Unlike arteries, which handle blood under high pressure due to the force generated by the heart, veins operate under much lower pressure. This difference is mainly because veins have a wider lumen and thinner walls, which helps accommodate the volume of blood being returned. Additionally, valves within veins prevent the backflow of blood, ensuring it moves in the correct direction toward the heart. This function is essential for maintaining proper circulation and volume of blood within the cardiovascular system.