Normally the human body has 6-7 Litres of blood given on the body type. About 60%-70% at any given time is circulating in the lower body which means our legs and below the waist. Due to this phenomenon over time. The veins have one direction opening valves that help control the backflow of the blood into the lower limbs. Unlike our arteries, the veins are less muscular compared to our arteries. Over the course of many years or after a pregnancy the veins will distend (widen) and not regain their shape and original narrowness. The valves do not close properly and become wider over the course of many years. This results in the blood flow backing up and the legs getting fluid filled swelling.