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Childhood Hodgkin lymphoma

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The lymphatic system

Childhood Hodgkin lymphoma (HL) 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, adenoid 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.

Diagram of the lymphatic system

Structure

The lymphatic system is made up of the following organs and tissues.

Lymph fluid

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 lymphatic fluid.

Lymphocytes

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 they mature, lymphocytes move to the lymph nodes and spleen.

Lymph vessels

Lymph fluid travels through the body in lymph vessels. There are 3 main types of lymph vessels. Lymphatic capillaries are tiny, closed-ended tubes through which fluid from body tissues enters the lymphatic system. Lymphatic 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

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 in the following major locations:

  • neck (called cervical lymph nodes)
  • chest (called thoracic and mediastinal lymph nodes)
  • armpit (called axillary nodes)
  • abdomen (called para-aortic, peri-aortic and mesenteric lymph nodes)
  • 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.

If a large number of particles are filtered through a lymph node or group of nodes, they may swell and become tender to the touch. For example, a sore throat may cause the lymph nodes under the jaw and in the neck to swell.

Spleen

The spleen is the largest lymphatic organ. It is in the upper-left abdomen.

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 and lymphocytes.

Thymus

The thymus is in the chest behind the breastbone, or sternum. It is where T cells mature and multiply.

Tonsils

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.

Adenoid

Although it is often called the adenoids, there is only one adenoid. It is a single, small mass of lymphatic tissue in the back of the nose that contains lymphocytes. It is also sometimes called the pharyngeal tonsil.

The adenoid helps the body fight infection by trapping bacteria and viruses.

The adenoid is present in infants and children. It starts to shrink just before puberty so that most adults don’t have the adenoid.

Bone marrow

Bone marrow is soft, spongy tissue in the centre of most bones. It contains immature 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.

Function

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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