Vein

A vein (vena) is a blood vessel that carries oxygen-poor blood back from the organs and tissues to the heart. Veins that are close to the heart, where the blood has to flow against gravity, have special valves.

What does a vein do?

The function of a vein is to carry oxygen-poor blood from the body back to the heart. This blood is then pumped to the lungs to take up oxygen again. It then flows via the pulmonary vein back to the heart. An artery carries the oxygen-rich blood from the heart to the organs and tissues.

Arteries are thicker, and blood flows through them faster. Blood pressure is therefore higher in arteries. Most arteries lie deeper in the body between muscles and other tissues, protecting them from external damage. Veins often lie more superficially and are sometimes visible under the skin.

Valves

Many veins have valves in them. These valves open only one way and ensure that the blood flows toward the heart. They prevent the blood from flowing back into the feet or legs and accumulating there when you stand upright or walk.

However, some veins, such as those in the brain, do not have valves. They lie above the level of the heart, so the blood automatically flows back to the heart under the influence of gravity.

Varicose veins

When the valves in the vein do not work properly, varicose veins develop. These are dilated, tortuous veins that are sometimes visible under the skin. The blood is not drained properly, which can cause pain, swelling, and fatigue. Examples include varicose veins in the legs, which often occur in people who stand or sit for long periods, during pregnancy, or due to overweight. Sometimes, treatment for varicose veins is necessary.