Anatomy of the vein system

An intricate network of blood vessels runs through the human body, transporting oxygen and nutrients, as well as the waste products of our metabolic processes.
In this vascular system, the heart pumps blood rich in oxygen into the arteries and, from these, into all organs and tissues in the body. Veins transport used blood back to the heart. Throughout this process, the arteries contain about 15% of the total blood volume, while the veins contain over 80%.

While the heart functions as a pump for transporting blood in the arteries, the veins require additional pumping mechanisms to counteract the force of gravity when the body is upright. The "calf muscle pump" plays the most important role in the transport of blood back to the heart. When we move, the calf muscles squeeze the veins together and force the blood against the force of gravity back in the direction of the heart.

The transport of blood back to the heart is also supported by the workings of the valves in our veins. These one-way flaps allow blood to flow in one direction only, thus preventing reverse blood flow back into the legs.

If these flaps do not close properly, blood flows back into the legs and pools in the veins, which become distended due to the increased pressure.
The condition where veins malfunction in this way is referred to as varicose veins, varicosis or venous insufficiency. Pronounced varicose veins lead to problems with the drainage of blood from the veins and to the complaints and complications that are typical of this condition. These include heavy legs, pain, swelling and, in extreme cases, open sores.