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).
Many veins, particularly those in the upper and lower limbs, have flaplike valves, which project inward from their linings. Valves are usually composed of two leaflets that close if blood begins to backup in the vein. These valves aid in returning blood to the heart, but close if it is in the opposite direction. Arteries do not contain valves.