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).
This allows blood to flow in both directions. When your muscles relax, the valves inside the damaged vein(s) will not be able to hold the blood. This can cause pooling of blood or swelling in the veins. The veins bulge and appear as ropes under the skin. The blood begins to move more slowly through the veins, it may stick to the sides of the vessel walls and blood clots can form.