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).
The arteries are the thickest of all blood vessels and have muscular walls that contract to keep the blood moving away from the heart. The veins are not as muscular, but they contain valves to prevent the blood from flowing backward.