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).
Varicose veins - Causes. Varicose veins are usually caused by weak vein walls and valves. Inside your veins are tiny one-way valves that open to let the blood through, and then close to prevent it flowing backwards. Sometimes the walls of the veins become stretched and lose their elasticity, causing the valves to weaken.