What structure prevents the blackflow of blood?

The structure that prevents the backflow of blood is called a valve. Valves are found in the heart and within the veins, ensuring that blood flows in one direction. In the heart, the atrioventricular and semilunar valves play crucial roles, while venous valves help maintain unidirectional flow back to the heart, especially in the limbs. These structures are essential for efficient circulation and preventing any reverse flow of blood.