The lymphatic system is a network of tiny vessels, similar to the blood circulation. However instead of blood, the lymph vessels carry a clear, straw-coloured fluid called lymphatic fluid (lymph). This fluid originates in the bloodstream and seeps through the walls of tiny blood vessels. It bathes and nourishes the body’s tissues. Lymph collects in the lymphatic vessels and eventually returns to the bloodstream.
What does the lymphatic system do?
The lymphatic system is part of the immune system and serves as one of the body’s defences against infection. It also helps fight abnormal cells, such as cancer cells. The lymphatic system also helps regulate fluid levels in the body.
The lymphatic system is made up of the lymphatic vessels, the lymph nodes and some organs, including the spleen and the tonsils.
The lymphatic vessels branch throughout all of the body, just like the blood circulation, but the vessels are much finer. These vessels carry the lymph. The vessels can have valves, like blood vessels, to stop backflow of lymph. Lymphatic vessels are usually coloured green on anatomical diagrams.
The lymph nodes (glands) are bean-shaped collections of tissue along the lymphatic vessels, such as the clusters in the groin, armpit and neck. Often the first time a person becomes aware of their lymph nodes is when they have swollen glands in the neck. The lymph nodes contain large numbers of white blood cells such as macrophages and lymphocytes. The lymph nodes act as filters, detecting and trapping foreign particles, cellular waste, toxins, bacteria and viruses, which can then be destroyed by the white blood cells.
Organs of the lymphatic system
The tonsils, adenoids and spleen are also involved in fighting infection and consist mainly of lymphatic tissue. The tonsils are a pair of soft tissue lumps at the back of the throat. The adenoids are a similar pair of lymph nodes that sit behind the nose. The spleen is situated in the abdomen and filters the blood, recycling old blood cells and removing some bacteria.
Conditions that can affect the lymphatic system
An infection can cause the number of disease-fighting white blood cells in the lymph nodes to increase rapidly. This may cause the node to swell, become tender and, sometimes, red.
The main areas where this is noticeable are the neck, groin and axilla (armpit). Thus an infected finger might result in swollen glands in the armpit on that side. Swollen glands in the neck are often caused by upper respiratory tract infections such as the common cold, a throat infection or glandular fever (infectious mononucleosis).
Lymphadenitis is the name for swollen, inflamed lymph nodes caused by an infection in the node, while lymphadenopathy is general swelling of lymph nodes. Infection of the lymph vessels is known as lymphangitis, which is most often caused by a bacterial skin infection.
As well as dealing with infections, lymph nodes can also trap cancer cells and try to destroy them, reducing their spread through the body. However, sometimes the cancer cells are not destroyed and can start to grow in the lymph nodes. Following a cancer diagnosis, the lymph nodes close to the original cancer site are usually examined to determine whether the cancer may have spread.
Cancer that starts in the lymphatic system itself is called lymphoma. The 2 main types of lymphoma are Hodgkin lymphoma and non-Hodgkin lymphoma. The first symptom of lymphoma is usually a swelling or lump in the lymph nodes – most often noticed in the neck, under the armpits, just above the collarbone, or in the groin area.
Lymphoedema is a condition where the lymphatic system is blocked or not working properly, causing an accumulation of lymphatic fluid in the body’s tissues. The build-up of lymphatic fluid causes swelling (oedema) that usually affects the arms or legs. Lymphoedema of the arm is sometimes a side-effect of surgery or radiotherapy treatment for breast cancer.