What is the lymphatic system?

To fully understand lymphoedema, it helps to first know a bit about the lymphatic system.

The lymphatic system helps to protect us from infection and disease. It’s part of the body’s immune system. Lymph fluid passes through lymph nodes which are connected by a network of lymph vessels. The nodes are found throughout the whole body.

Lymphatic system
Lymphatic system

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The lymphatic system:

  • acts as a one-way drainage system transporting fluid from body tissues into the blood circulation
  • contains white blood cells called lymphocytes, which fight infection
  • gets rid of waste products produced by cells.

Lymph fluid

This is a colourless fluid that forms in our body and surrounds all our body’s tissues. Extra fluid that comes from the body’s tissues drains into small lymph vessels. It flows constantly through the lymph vessels and is filtered through the lymph nodes. The fluid then drains back into the bloodstream.

Lymph nodes

Lymph nodes are found throughout the body, but mainly in the neck, armpits, groin and tummy (abdomen). They filter and break down bacteria (germs) or other harmful cells from the lymph fluid.

Lymph nodes vary in size. Some are as small as a pinhead and others are about the size of a baked bean. The number of lymph nodes in the body differs from person to person.

Different parts of the body have different numbers of nodes. For example, there are about 15–30 small nodes in the armpit.

Lymph vessels

Lymph vessels are a network of tubes that connect to groups of lymph nodes throughout the body. Some vessels are just under the skin and can easily be damaged if the skin is broken.

The fluid travels through the lymph vessels and drains into the bloodstream.

How the lymphatic system works

Lymph fluid normally flows through the network of lymph vessels that connect to a group of lymph nodes. The nodes act as a filter, destroying or trapping anything harmful that the body doesn’t need. The lymph nodes contain white blood cells (lymphocytes), which attack and break down bacteria, viruses, damaged cells or cancer cells.

Waste products and the destroyed bacteria are then carried in the lymph fluid back into the bloodstream and are removed from the body with other body waste.

Lymph nodes sometimes trap bacteria or viruses that they cannot destroy straight away. When you have an infection, lymph nodes often swell and become tender and sore to touch as they fight infection.

Sometimes, cancer cells spread into the lymph nodes from a cancer that’s in another part of the body. It’s also possible for a cancer to start in the lymph nodes themselves. This is called lymphoma. If this happens, the lymph nodes become swollen but are usually painless.

There are different causes of swollen lymph nodes, but if you develop a painless, swollen lymph node it’s important to have it checked by your GP.