The lymphatic system

The lymphatic system helps protect us from infection and disease. Sometimes cancer cells can travel through lymph fluid to other parts of the body.

What is the lymphatic system?

The lymphatic system helps protect us from infection and disease. It is part of the body’s immune system. Lymph fluid passes through lymph nodes. A network of lymph vessels connects the lymph nodes together. You have nodes throughout your body.


The lymphatic system

The lymphatic system of the head and neck


The lymphatic system does different things:

  • it acts as a one-way drainage system – this means it moves fluid from body tissues into the blood circulation

  • it contains white blood cells called lymphocytes, which fight infection

  • it gets rid of any waste that cells make.

How the lymphatic system works

Lymph fluid normally flows through a network of lymph vessels. These lymph vessels connect to a group of lymph nodes. The nodes act as a filter. They trap or destroy anything harmful that the body does not need.

Inside the lymph nodes are white blood cells, also called lymphocytes. These white blood cells attack and break down bacteria, viruses, damaged cells or cancer cells.

The lymph fluid carries the waste products and destroyed bacteria back into the bloodstream. The liver or kidneys then remove these from the blood. The body passes them out with other body waste, through bowel movements (poo) or urine (pee).

Lymph nodes sometimes trap bacteria or viruses that they cannot destroy straight away. For example, they may do this when you have an infection. When the lymph nodes are fighting the infection, they often swell and become sore to touch.

Sometimes cancer cells spread from where a cancer started (the primary site) to other parts of the body. They can travel around the body in the blood or through lymph fluid. When these cancer cells reach another part of the body, they may grow and form another tumour. This is called a secondary cancer or a metastasis.

Cancer cells can sometimes spread into the lymph nodes from a cancer somewhere else in the body. This is called secondary cancer in the lymph nodes. Cancer can also start in the lymph nodes themselves. This is called lymphoma. If there is cancer in the lymph nodes, they may swell, but are usually painless.

There are different causes of swollen lymph nodes. But if you notice a painless, swollen lymph node, it is important to get it checked by your GP.

Lymph vessels, lymph fluid and lymph nodes

  • Lymph vessels

    Lymph vessels are a network of tubes. These tubes connect to groups of lymph nodes throughout the body. Some vessels are just under the skin. This means breaking the skin can easily damage them. Lymph fluid travels through the lymph vessels and drains into the bloodstream.

  • Lymph fluid

    This is a colourless fluid that is made in the body. It surrounds all body tissues. Extra fluid from tissue in the body drains into and flows through small lymph vessels. This fluid is filtered through the lymph nodes, and drains back into the bloodstream.

  • Lymph nodes

    There are lymph nodes throughout your 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 to 30 small nodes in the armpit.