What function do veins serve in the circulatory system?

Veins play a crucial role in the circulatory system by carrying blood back to the heart. This is an essential function because after blood is circulated through the body and has delivered oxygen and nutrients to the tissues, it needs to return to the heart to be re-oxygenated in the lungs. Veins are equipped with valves that prevent the backflow of blood, ensuring it moves efficiently toward the heart, even against the force of gravity in certain parts of the body.

By transporting deoxygenated blood (with the exception of pulmonary veins, which carry oxygenated blood from the lungs to the heart), veins complete the systemic circulation cycle, which is vital for maintaining overall health and supporting the body's cellular functions. Understanding this function highlights the importance of veins in the overall process of circulation, in contrast to other components such as arteries, which are responsible for carrying blood away from the heart, and the heart itself, which pumps blood throughout the body.