What is the lymphatic system?

The lymphatic system is a drainage system that helps your body get rid of excess fluid and waste products. It also contains white blood cells and helps fight infection and disease. It is made up of:

  • Lymph fluid – formed when excess fluid drains from the body.
  • Lymph vessels – tiny channels that run through the body and carry lymph fluid.
  • Lymph nodes – small glands connected by lymph vessels that are found throughout the body but especially in the neck, armpits, groin and abdomen.
  • Lymph nodes act as filters. They trap or destroy bacteria, viruses, damaged cells or cancer cells as the lymph fluid flows through them. They contain cells that help fight infection and diseases such as cancer.

When lymph nodes swell, it’s normally a sign of an infection.

Sometimes, cancer cells spread into the lymph nodes from somewhere else in the body. Cancer can also start in the lymph nodes (lymphoma).

Lymph nodes may swell for various reasons. However, if you develop a painless, swollen lymph node, it is important to get it checked by your doctor.

Role and composition of the lymphatic system

The lymphatic system is made up of groups of lymph nodes throughout the body, which are connected by a network of lymph vessels.

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.

The lymphatic system
The lymphatic system

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Lymph fluid

This is the liquid that flows through the lymph vessels and the lymph nodes. It forms when excess liquid, from the fluid that surrounds all our body tissues, drains into small lymph vessels.

Lymph vessels

Lymph vessels are a network of tubes that go all over the body. Some are tiny channels just under the skin, which can be easily damaged if the skin is broken. Small lymph vessels join together to form larger lymph vessels, which pass through lymph nodes. The fluid then travels through larger lymph tubes and drains into the bloodstream.

Lymph nodes

Lymph nodes are found throughout the body, but mainly in the neck, armpits, groin and tummy (abdomen). They’re made of tissue that contains special cells that help fight infection and disease such as cancer.

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 varies 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.

How the lymphatic system works

Lymph fluid flows through the lymph nodes, which act as a filter destroying or trapping anything harmful that the body doesn’t need. This includes bacteria, viruses, damaged cells or cancer cells.

Lymph nodes contain white blood cells (lymphocytes), which attack and break down bacteria or other harmful cells. Waste products and the destroyed bacteria are then carried in the lymph fluid into the bloodstream and are disposed of with other body waste.

Sometimes, the lymph nodes trap bacteria or viruses that they can’t destroy immediately. The lymph nodes then swell and become tender and sore to touch. This is usually the sign of an infection that may need treatment with antibiotics.

Sometimes, cancer cells spread into the lymph nodes from a cancer in another part of the body. It’s also possible for a cancer to start in the lymph nodes themselves (lymphomas). 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.