Your superficial venous system (found between the skin and the muscles) transports 10% of the blood upwards to your lungs and heart. It is from this system and its main vessels, the Great and Small Saphenous Veins, that varicose and spider veins come from.
Veins have one-way valves that direct the blood upward, pumped by your calf muscle. If those valves fail to close properly an abnormal flow of blood back down your legs, called reflux, develops, giving you Chronic Venous Insufficiency (CVI). The reflux puts excessive pressure on the vein’s walls, which causes them to expand and bulge, and fluid leaks into the surrounding tissues.
When you take a step your calf muscle squeezes, forcing the blood inside the veins up the leg towards the heart—in the correct direction. (The calf muscles are the “heart pump” for the leg veins.) When gravity takes over and the blood starts to fall back down towards the toes, the valves inside the veins should snap shut and prevent the blood from going back down the leg.
When you have abnormal veins, those valves do not work correctly, and the blood rushes back down the leg, causing high pressure inside the leg veins. This high pressure causes inflammation and the painful symptoms of vein disease as well as the skin rashes and ulcers and blood clots.