An anatomical feature found in larger veins that prevents backflow is known as what?

• A. Lumen size
• B. Muscles
• C. Valves
• D. Elastic tissue

Answer: (C)

Valves in veins act as one-way gates to stop backflow. They are folds of the inner lining that form cusps, opening to let blood flow toward the heart and closing if it starts to move backward. This is especially important in larger veins of the legs, where blood must travel upward against gravity. The valves work with the skeletal muscle pump—when muscles contract, they squeeze the veins and push blood forward, while the valves prevent it from pooling or reversing direction when the muscles relax. Lumen size and elastic tissue contribute to how easily blood moves, and muscle action helps propulsion, but the feature that directly prevents backflow is the valve cusps.