Why Do Veins Have Valves and Arteries Do Not?

Emily Hildebrand/CC-BY 2.0

Veins have valves to prevent blood from flowing backwards and pooling, whereas arteries pump blood at higher pressures, which naturally prevents backflow. Veins need valves to keep blood flowing in one direction because the flow is less constant; the flow in arteries is constant and requires artery walls to be more flexible and strong enough to accommodate the high pressures.