What is the primary function of venous valves?

The primary function of venous valves is to maintain unidirectional blood flow towards the heart. These valves are located within the veins, particularly in the arms and legs, and they open to allow blood to flow toward the heart while closing to prevent backflow. This is crucial in the venous system, where blood is flowing against the force of gravity, especially in the lower extremities.

When a person stands or sits for long periods, venous valves help ensure that blood does not pool in the lower legs. The contraction of surrounding muscles during physical activities also aids in pushing the blood upwards towards the heart, assisted by the closure of the valves. This mechanism prevents venous stasis and contributes to effective circulation throughout the body.

The other options represent different functions unrelated to the role of venous valves. While arteries do regulate blood flow and blood pressure, these are primarily controlled by different mechanisms involving arterial walls and systemic vascular resistance, rather than venous valves. Filtering blood particles is a function attributed more to the lymphatic system and the spleen rather than the venous system.