The lymphatic system:

• acts as a one-way drainage system to transport excess fluid from body tissues into the blood system
• contains cells which fight infection (lymphocytes)
• gets rid of waste products (chemicals) produced by cells.

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

Lymph nodes are also called lymph glands.

The lymphatic vessels and lymph nodes contain a milky liquid called lymph. Lymph is formed when some of the colourless liquid that surrounds all body tissues drains from the tissues into small lymph vessels, which lie between the cells.

The small lymph vessels join together to form larger lymph vessels, which pass through a number of lymph nodes. In the lymph nodes, bacteria and harmful substances are broken down. The fluid then travels through larger lymph ducts and drains into the bloodstream.

Lymph nodes are found throughout the body, but mainly in the neck, armpit, groin and abdomen. They are made of lymphoid tissue. This tissue contains special cells that can help to fight infection and other diseases 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 also have different numbers of nodes: in the armpit, for example, there will be about 15-30 small nodes. At the back of the abdomen there are several large nodes.

As lymph flows through the lymph nodes, the nodes collect and filter out anything the body does not need or that could harm it. This includes bacteria, viruses, other infectious organisms, damaged cells or cancer cells.

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

Sometimes the lymph nodes trap bacteria or viruses that they cannot destroy immediately. The lymph node will then usually swell and become hot, painful and sore when touched. This can usually be treated with antibiotics.

Sometimes the lymph nodes will develop or trap cancer cells that they cannot destroy. The cancer cells may then continue to divide and produce new cells within the node. If this happens, the swollen nodes are often painless and are not uncomfortable when touched. Some cancers start in the lymphatic system, in which case they are called lymphomas. Sometimes the cancer cells may spread into the lymph glands from a cancer in another part of the body, such as the breast, lung or bowel.

It is important to check with your doctor if you have a painless, swollen lymph node, although the swelling is likely to be caused by something other than cancer.