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What the lymphatic system is

The lymphatic system is a system of thin tubes that runs throughout the body. These tubes are called lymph vessels or lymphatic vessels.

Diagram of the lymphatic system

The lymphatic system is like the blood circulation - the tubes (vessels) branch through all parts of the body like the arteries and veins that carry blood. But the lymphatic system tubes are much finer and carry a colourless liquid called lymph.

Lymph is a clear fluid that circulates around the body tissues. It contains a high number of lymphocytes (white blood cells). Plasma leaks out of the capillaries to surround and bathe the body tissues. This then drains into the lymph vessels.

Diagram of a lymphatic capillary

The fluid, now called lymph, then flows through the lymphatic system to the biggest lymph vessel - the thoracic duct. The thoracic duct then empties back into the blood circulation.

 

Lymph glands

Along the lymph vessels are small bean-shaped lymph glands or 'nodes'.

Diagram of a lymph node

You can probably feel some of your lymph nodes. There are lymph nodes in many parts of your body including

  • Under your arms, in your armpits
  • In each groin (at the top of your legs)
  • In your neck

There are also lymph nodes that you cannot feel in

  • Your abdomen
  • Your pelvis
  • Your chest
 

Other lymphatic system organs

The lymphatic system includes other body organs. These are the

  • Spleen
  • Thymus
  • Tonsils
  • Adenoids

The spleen is under your ribs on the left side of your body. The spleen has two main different types of tissue, red pulp and white pulp.  The red pulp filters worn out and damaged red blood cells from the blood and recycles them. The white pulp contains many B lymphocytes and T lymphocytes. These are white blood cells that are very important for fighting infection. As blood passes through the spleen, these blood cells pick up on any sign of infection and begin to fight it.

The thymus is a small gland under your breast bone. The thymus helps to produce white blood cells. It is usually most active in teenagers and shrinks in adulthood.

Diagram showing the position of the thymus gland

The tonsils are two glands in the back of your throat. The adenoids are at the back of your nose, where it meets the back of your throat. The tonsils and adenoids (also called the 'nasopharyngeal' tonsils) help to protect the entrance to the digestive system and the lungs from bacteria and viruses.

Diagram showing the adenoids and tonsils

 

What the lymphatic system does

The lymphatic system does several jobs in the body. It

 

Draining fluid into the bloodstream

As the blood circulates, fluid leaks out from the blood vessels into the body tissues. This fluid is important because it carries food to the cells and waste products back to the bloodstream. The leaked fluid drains into the lymph vessels. It is carried through the lymph vessels to the base of the neck where it is emptied back into the bloodstream. This circulation of fluid through the body goes on all the time.

 

Filtering lymph

The lymph nodes filter the lymph fluid as it passes through. White blood cells attack any bacteria or viruses they find in the lymph as it flows through the lymph nodes. If cancer cells break away from a tumour, they often become stuck in the nearest lymph nodes. This is why doctors check the lymph nodes first when they are working out how far a cancer has grown or spread.

 

Filtering the blood

This is the job of the spleen. It filters the blood to take out all the old worn out red blood cells and then destroys them. They are replaced by new red blood cells that are made in the bone marrow. The spleen also filters out bacteria, viruses and other foreign particles found in the blood. White blood cells in the spleen attack bacteria and viruses as they pass through.

 

Fighting infection

When people say "I'm not well, my glands are up" they are really saying they have swollen lymph nodes because they have an infection. The lymphatic system helps fight infection in many ways such as

  • Helping to make special white blood cells (lymphocytes) that produce antibodies
  • Having other blood cells called macrophages inside the lymph nodes which swallow up and kill any foreign particles, for example germs

This function of the lymphatic system is really part of the immune system. There is more about this in the the immune system section of CancerHelp UK.

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Updated: 10 February 2014