The lymphatic system
Childhood non-Hodgkin lymphoma (NHL) is a type of cancer that starts in the lymphatic system. The lymphatic system is made up of a network of lymph fluid, lymphocytes, lymph vessels, lymph nodes and the lymphatic organs. These organs are the spleen, thymus, tonsils, adenoids and bone marrow. Lymphatic tissue is also found in other parts of the body, including the stomach, intestines and skin. Organs and tissues in the lymphatic system make and store cells that fight infection and diseases. The lymphatic system works with the circulatory system (made up of the heart and bloodstream) and other parts of the immune system to keep the body healthy.
The lymphatic system is made up of the following organs and tissues.
Lymph fluid is a clear, yellowish fluid that carries lymphocytes, macrophages and other white blood cells. It also carries proteins and nutrients. Lymph fluid travels throughout the body in a network of lymph vessels and bathes body tissues. It may also be called lymph or lymphatic fluid.
Lymphocytes are a type of white blood cell. They fight viruses, bacteria, foreign substances or abnormal cells (including cancer cells). The 2 types of lymphocytes are:
- B cells make antibodies to fight infections.
- T cells fight infection, destroy abnormal cells and control the immune response.
All lymphocytes start to develop in the bone marrow. B cells stay in the bone marrow to mature. T cells move to the thymus to mature. After maturing they move to the lymph nodes and spleen.
Lymph fluid travels through the body in lymph vessels. There are 3 main types of lymph vessels. Lymph capillaries are tiny, closed-ended tubes through which fluid from body tissues enters the lymphatic system. Lymph vessels are tubes that move lymph fluid to and from the lymph nodes. Collecting ducts are tubes that return lymph fluid to the bloodstream.
Lymph nodes are small, bean-shaped organs that sit along lymph vessels and filter lymph fluid. Lymph nodes vary in size, but they are usually less than 1 cm. (They can be up to 1.5 cm in size in the groin.)
There are many lymph nodes throughout the body. The number of lymph nodes varies from one part of the body to another. Lymph nodes are located in groups mainly in the following locations:
- the neck (called cervical lymph nodes)
- the chest (called thoracic and mediastinal lymph nodes)
- the armpit (called axillary nodes)
- the abdomen (called para-aortic, peri-aortic and mesenteric lymph nodes)
- the groin (called inguinal lymph nodes)
The lymph nodes filter harmful particles from the lymph fluid before returning it to the bloodstream. These particles include bacteria, viruses and foreign substances.
The other main function of the lymph nodes is to activate the immune system. Lymph nodes contain 2 types of white blood cells that fight invading micro-organisms. Lymphocytes attack viruses, bacteria and other micro-organisms. Macrophages surround and destroy foreign substances, damaged cells and bits of broken cells.
Lymph nodes often get bigger when they fight an infection. They may also become tender to the touch. For example, a sore throat may cause the lymph nodes under the jaw and in the neck to swell.
The spleen is the largest lymphatic organ. It is in the upper-left abdomen. The spleen contains lymphocytes and macrophages that help the body to fight infection.
The spleen filters the blood by removing old red blood cells, lymphocytes and invaders (such as viruses and bacteria). The spleen also stores red blood cells.
The thymus is in the chest behind the breastbone, or sternum. It is where T cells mature and multiply.
The tonsils are small masses of lymphatic tissue that contain lymphocytes. The palantine tonsils are in the back of the mouth. We also have another pair of tonsils on the base of the tongue (called the lingual tonsils).
The tonsils help the body fight infection by trapping bacteria and viruses. They also make antibodies.
Although it is called adenoids, it is a single, small mass of lymphatic tissue in the back of the nose. It is also sometimes called the pharyngeal tonsil.
The adenoids contain lymphocytes and help the body fight infection by trapping bacteria and viruses.
The adenoids are present in infants and children, and start to shrink just before puberty. They are usually absent in adults.
Bone marrow is soft, spongy tissue in the centre of most bones. It contains immature blood cells called stem cells. These stem cells develop into red blood cells, white blood cells or platelets. Red blood cells carry oxygen to and carbon dioxide from tissues in the body. White blood cells help the body fight infection and diseases. Platelets help blood to clot.
Lymphatic tissue in the digestive system
There is also lymphatic tissue in the organs of the digestive system, such as the stomach and small intestine. This lymphatic tissue contains B cells and T cells that attack viruses, bacteria and other micro-organisms in the digestive system.
The lymphatic system:
- moves extra fluid out of tissues and into the bloodstream
- helps defend the body against disease
- helps move hormones and nutrients throughout the body
- helps remove waste products from tissues
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