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).
Veins need valves to keep blood flowing in one direction because the flow is less constant; the flow in arteries is constant and requires artery walls to be more flexible and strong enough to accommodate the high pressures.The valves in veins allow blood flow in one direction while blocking any counter-flow.