Veins are responsible for returning deoxygenated blood back to the heart after it has circulated through the body. Unlike arteries, veins have valves that prevent backflow, ensuring unidirectional blood flow despite low pressure. Their walls are thinner and less muscular than arteries, allowing them to accommodate varying blood volumes. This function is critical during surgeries involving venous access or repair, where preserving valve integrity prevents complications such as venous insufficiency or thrombosis. Clinically, understanding vein anatomy is essential for procedures like central line placement and varicose vein treatments.

Reference: Gray's Anatomy, Henry Gray, 42nd Edition.