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).
Little valves are there to prevent back flow caused by gravity, and when these valves fail, that is what causes varicose veins. The blood backs up a bit, enlarges the vein and the bulges in the vein are where the valve tissue is. Source(s): masters in human physiology, retired AP bio and physiology teacher.