Which term describes valves that prevent the backflow of blood in the circulatory system?

The term that best describes valves that prevent the backflow of blood in the circulatory system is semilunar valves. These valves are located at the exits of the heart and are positioned between the ventricles and the major arteries (the aorta and pulmonary artery). Their primary function is to ensure that when the ventricles contract and pump blood out of the heart, it flows in one direction towards the arteries and does not return back to the ventricles.

When the ventricles relax, the semilunar valves close, preventing any backflow of blood into the heart. This mechanism is crucial for maintaining efficient circulation and ensuring that blood flows smoothly through the cardiovascular system.

While other valves in the heart, such as the tricuspid and atrioventricular valves, also play roles in directing blood flow and preventing backflow, they specifically function in the context of blood flow between the heart's chambers (the atria and ventricles), rather than at the exit points to the arteries. Venous valves, on the other hand, are involved in preventing backflow in the veins but are not located in the heart itself. Therefore, the semilunar valves are the key structures that fulfill the function described in the question.