Legs veins have one-way valves throughout their lengths, extending from the ankles to the groins, These valves prevent blood from flowing backwards as it moves up the legs
In essence, it is like a step ladder where blood gets pumped up into a higher level by the “leg pump” and the valve below this level closes so that blood does not go back down to the lower level. Eventually, blood clears the saphenofemoral junction and the saphenopoliteal junctions where it joins the deep veins of the leg.
There are also connections between the superficial (under the skin surface) and deep veins, and these connections have valves – more on these perforator veins later. Venous reflux, also known as venous insufficiency occurs when these vein valves leak.