How does the circulatory system ensure that blood flows in one direction?

The circulatory system ensures that blood flows in one direction primarily through the presence of valves within the heart and veins. Heart valves, such as the atrioventricular and semilunar valves, open and close in response to pressure changes, preventing backflow as blood is pumped from the atria to the ventricles and out to the body. Similarly, venous valves prevent the backward flow of blood as it returns to the heart, especially against the force of gravity. This coordinated mechanism maintains efficient and unidirectional blood flow throughout the circulatory system.