What is the function of veins in the circulatory system?

Veins serve the essential function of returning impure or deoxygenated blood back to the heart. In the circulatory system, veins carry blood that has delivered oxygen and nutrients to the body's tissues and collected carbon dioxide and other waste products. This deoxygenated blood then flows through the veins, which are structured with valves to prevent backflow, and ultimately enters the heart to be sent to the lungs for re-oxygenation.

In contrast to veins, arteries are responsible for carrying oxygenated blood away from the heart to supply the body with necessary nutrients. Gas exchange occurs primarily in the capillaries, which connect arteries and veins, where oxygen and carbon dioxide are exchanged at the tissue level. Additionally, blood filtration is a function performed by the kidneys rather than veins. Thus, the role of veins in supporting the circulatory system is critical in maintaining blood circulation back to the heart for re-oxygenation.