Final answer:
Veins have valves that prevent backward blood flow which is crucial for returning blood to the heart, especially from the lower parts of the body. Arteries, which transport blood away from the heart, have thicker walls to sustain the high-pressure blood flow and do not have valves like veins do.
Step-by-step explanation:
Valves within the circulatory system are essential as they ensure one-directional blood flow, thereby preventing blood from flowing backward. These valves are not only present in the heart but also in parts of the peripheral circulatory system. Specifically, veins are equipped with valves that fulfill this function. Unlike the heart that relies on muscular contractions to propel blood, the veins depend on these valves in conjunction with skeletal muscle actions and pressure changes during breathing to ensure that blood flows back to the heart. This is critical, especially in the extremities, where blood must travel against gravity on its return to the heart.
Comparatively, arteries do not possess valves like veins do because the pressure from the heart's contractions is sufficient to keep blood flowing in the right direction. Instead, the structure of the arteries includes thicker walls to withstand the higher pressure exerted by the pumping heart. The main role of the arteries is to transport blood away from the heart to the rest of the body. The arterial system's high-pressure environment negates the need for valves within these vessels.