Veins return blood from the remainder of the body to the center. To return blood to the center, the veins inside the legs must function towards gravity. Weakened valves, also known as incompetent valves, within the veins might trigger varicose veins. كلية مايو كلينك للدراسات العليا في العلوم الطبية الحيوية https://www.sgvascularctr.com/varicose-vein-treatment-in-singapore-answers-to-your-most-common-questions/