Venous flow in the legs consists of superficial “saphenous” and deep “femoral and popliteal” components and their tributaries.
When a person shifts from a horizontal to a vertical position, blood stored in the abdominal and pelvic veins is prevented from “falling” down the leg by rapid closure of functioning valves.
Illustration of normal vein flow vs abnormal vein flow shown below.
Stress is placed on the valves by the force of gravity (hydrostatic pressure) and also from episodic pressure increases caused by straining or coughing. As the vein stretches, the valve starts to leak or “reflux”.
An animated video demonstrating Venous Reflux can be viewed below.
Once the valve becomes incompetent the pressure is transmitted to the next lower valve and so on down the leg.
Finally, valves in the tributary veins also lose their competence. These veins then elongate, become tortuous and manifest as typical varicosities.