Your leg veins

This section looks at normal veins and how they function within the body. It concentrates on leg veins although we have included a section which provides a general overview about the venous system. 

What are veins?

Your veins or to be more precise, your venous system, is a network of blood vessels in the human body which transport deoxygenated blood ("used" blood which contains waste products) towards the heart.

Each vein is a slim tube which consists of the following:

  • Inner space or "lumen"
  • Outer layer of connective tissue or "tunica externa"
  • Rings of smooth muscle or "tunica media"
  • Inner lining of endothelial cells or "tunica intima"

Most of the veins contain valves: these valves are a type of one way valve flap which prevents blood from flowing back and collecting in your lower extremities (legs).

These valves act against the forces of gravity. They open to allow blood to travel towards the heart and then close as blood flows through that vein to stop any backwards flow. This is a particular feature of leg veins.  

Your venous system contains large and small veins. The large veins are located alongside the arteries but differ in one important aspect: your veins transport blood back to the heart whereas your arteries transport blood away from the heart.

Your veins act as a reservoir for the majority of your blood supply.

Four types of veins

There are four categories of veins which include:

  • Deep veins
  • Superficial veins
  • Pulmonary veins
  • Systemic veins

Deep veins

These are as the name says: they are located deep in the muscles, wrapped in a fascial (strands) layer and run alongside the arteries.

Superficial veins

These veins are visible underneath the skin and connect to deep veins at points behind the knee and in the groin via the perforator veins. Perforator veins act as a junction between the deep and superficial veins.

Pulmonary veins

These veins transport oxygenated ("fresh") blood from the lungs to the heart.

Systemic veins

These veins drain deoxygenated ("used") blood from many areas of the body which is then transported to the heart.

Circulation of the blood

Oxygen-rich blood is circulated around the body via the arteries and veins. This blood is pumped from the heart and through the arteries to the legs.

Once it has switched its nutrients and oxygen into capillaries (smallest of all the blood vessels) this deoxygenated blood then enters the veins through a series of venules (tiny blood vessels). These venules act as a junction between the capillaries and the veins.

Deoxygenated blood contains carbon dioxide and other waste products. It is transported back to the heart where it flows into the pulmonary veins and then the lungs.

This is a continuous cycle.

Basically, your circulation is controlled by your arteries and veins. The arteries transport blood from your heart to the organs and tissues of the body: the veins return used blood (deoxygenated) blood to your heart. 

Function of the veins

To put it simply: the veins enable blood to be transported from the internal organs of the body to the heart. This blood travels through a system of veins which ensure that it flows upwards to the heart rather than pooling in the lower half of the body.

The muscles in the legs "pump"  this blood up into the upper half of the body and towards the heart. This action takes place in the veins which then compress as they do so. But once these muscles relax, the veins do as well which means that blood would flow down into the extremities but for the action of valves present in these veins.

Each vein contains this single direction valve which is designed to stop this from happening. If this is working as normal then the veins are defined as "competent".

But if the valve does not work properly then they are said to be "incompetent". 


This contraction of the leg muscles is an important part of the process which is why walking is advocated as a means of keeping fit as well as preventing varicose veins.

Problems with the veins

The problem arises when blood is unable to flow properly from the superficial veins to the deep veins. This causes pressure to build up in these veins which causes blood to pool in the lower body.

This is better known as varicose veins.

Defective valves in the veins allow blood to flow back into the lower half of the body rather than preventing this. This is called "venous reflux". 

It is the main cause of varicose veins.

Guide to Varicose Veins

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