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How Veins Work


How veins work - Blood flow DiagramThe legs, like any other part of the body, need a blood supply.

The heart pumps blood that is full of oxygen and food to the tissues through blood vessels called arteries.

The blood gives up oxygen and nutrients to the muscles and tissues in the legs and then returns to the heart through the veins.

The heart can pump blood to the legs and so, unless the arteries are blocked, the blood gets to the feet fairly easily through the arteries.

However getting blood back from the legs isn’t so easy. To get back to the heart, the blood needs to flow up hill against gravity. There is no automatic “heart” in the leg that can pump the heart back and so the body needs a different way to get blood back to the heart.

This section helps explain how veins work and how they get blood back to the heart from the legs.


How Veins Work: Normal Veins and Valves

How veins work - Animation of how normal valves work when the leg muscles are pumping during walking

How normal valves work when the leg muscles are pumping during walking

For veins to pump blood uphill against gravity, there needs to be movement. This movement is supplied by the movement of the leg muscles during walking or exercise. During movement, the muscles push on the veins, “squashing” them and squirting blood up and out of the veins. This results in the blood getting forced upwards into the pelvis against gravity.

However, when the muscles relax and the veins relax open again, the blood should rush back into the leg with gravity, if it weren’t for one-way valves stopping it.

These valves are like little “pockets” on the vein wall. They point upwards. when blood is pumped upwards, they are forced open. However when blood starts to fall back downwards with gravity, the valves open to stop this from happening.

If blood falls back down the leg veins, it is called “reflux” (or “venous reflux”). It is venous reflux that is the major cause of most venous diseases. Venous reflux is almost always the cause of varicose veins.

If you want to understand venous reflux better, it is explained easily in the book: “Understanding Venous Reflux – The Cause of Varicose Veins and Venous Leg Ulcers“.


How Veins Work: Abnormal Veins and Valves

When valves in a vein fail and they let blood reflux back down the vein, they are said to be ‘incompetent’.

In this situation, the muscles squeeze the vein and the blood is forced up and out of the vein, as in normal veins.

However, when the muscles relax and the veins dilate again, the blood starts to fall back down the leg by gravity. In patients with varicose veins, the faulty valves are not able to prevent it. This failure of the valves and the backwards flow of venous blood is called venous ‘reflux’.

Venous reflux doesn’t only cause varicose veins. It can also cause aching legs, swollen legs, venous eczema, phlebitis, thread veins (spider veins), red or brown skin stains at the ankles and venous leg ulcers.

There are 3 types of faulty valves shown here:

Vein valves failing to close causing venous reflux - a cause of varicose veins

Vein valves failing to close causing venous reflux – a cause of varicose veins

Damaged vein valves causing venous reflux - a cause of varicose veins

Damaged vein valves causing venous reflux – a cause of varicose veins

Failing vein valves causing venous reflux - a cause of varicose veins

Failing vein valves causing venous reflux – a cause of varicose veins