What are two instances where valves are important in to circulatory system?

Valves are crucial in the circulatory system to ensure unidirectional blood flow and prevent backflow. In the heart, the atrioventricular and semilunar valves maintain proper blood flow between the atria and ventricles, as well as into the arteries. Additionally, venous valves in the limbs help maintain blood return to the heart against gravity, particularly during physical activity. Both instances are vital for efficient circulation and overall cardiovascular health.