Leg veins

This section looks at the structure and function of the vascular system. It is an overview of how this system works with a particular focus on the smallest blood vessels or capillaries. If these capillaries become enlarged or broken then they result in the condition we know as thread veins.


The capillaries are the smallest blood vessels in the body. They along with veins and arteries form the vascular system: a network which is responsible for the circulation of the blood.

The capillaries allow wastes, oxygen and nutrients to be exchanged between the blood and cells of the body. They supply essential nutrients to an internal organ and remove waste products from that same organ.

Basically, the capillaries act as a junction between tiny arteries (arterioles) and tiny veins (venules). They allow blood to flow between the two.

Each capillary is around one cell thick. This means that blood cells can only pass through it in single file. It also means that they are fragile and easily damaged.

Vascular system

This system works by circulating blood to and from the heart which is vital for our existence.

It enables oxygenated (fresh) blood to travel from the heart to cells within the body which then supply the internal organs. Used or deoxygenated blood travels from these organs back towards the heart.

Blood is transported from the heart and through the arteries to the rest of the body. It is returned to the heart through the veins.

How does it do this?

The blood leaves the heart through the arteries which then branch off into narrow arterioles (tiny arteries) and branch off even further into the capillaries.

Once the blood has reached the cells and tissues of the body it returns via the capillaries. These capillaries join together to form the wider venules which widen even more to form the veins.

Guide to Thread Veins

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