WASHINGTON, DC - JANUARY 20: U.S. President Donald Trump delivers his inaugural address on the West Front of the U.S. Capitol on January 20, 2017 in Washington, DC. In today's inauguration ceremony Donald J. Trump becomes the 45th president of the United States.
One-Way Valves in the Veins. One-way valves consist of two flaps (cusps or leaflets) with edges that meet. These valves help veins return blood to the heart. As blood moves toward the heart, it pushes the cusps open like a pair of one-way swinging doors (shown on the left).
Veins have much thinner walls, because the blood they carry is under low pressure. VEINS have valves that aid the return of blood to the heart and prevent blood from going backwards. ARTERIES do not have valves, except for the semi-lunar valves of the pulmonary artery and the aorta. ARTERIES have relatively narrow lumens, VEINS have relatively wide lumens.