Non-Hodgkin lymphoma (NHL) is a type of cancer that starts in the lymphatic system. The lymphatic system works with the circulatory system and the immune system – the body's natural defence against infection and disease. It is made up of the spleen, thymus, tonsils, adenoids, bone marrow and a network of lymph nodes throughout the body that are connected by lymph vessels. Lymphatic tissue (which stores infection-fighting cells) is also found in other parts of the body, including the stomach, intestines and skin.
Structure
Lymph
Lymph (lymph fluid) is a clear, yellowish fluid that carries white blood cells (lymphocytes), antibodies and nutrients throughout the body. The lymph flows through the network of lymph nodes and vessels.
Lymphocytes
Lymphocytes are a type of white blood cell important to the body's immune system. There are 2 types:
- B cells (B lymphocytes) – make antibodies to fight an infection
- T cells (T lymphocytes) – regulate the immune system
Lymphocytes start to develop in the bone marrow. The B cells and T cells mature in different places:
- B cells – bone marrow or lymphatic organs
- T cells – thymus
Lymph vessels
There are 3 main types of lymph vessels:
- lymphatic capillaries – microscopic, closed-ended tubes where fluid from body tissues enters the lymphatic system
- lymph vessels – tubes that move lymph to and from the lymph nodes
- collecting ducts – tubes that return lymph to the bloodstream
Lymph nodes
Lymph nodes are small, bean-shaped organs that filter lymph. Lymph nodes vary in size, but are usually less than 2.5 cm (1 inch) across. There are many lymph nodes throughout the body. The number of lymph nodes varies from one part of the body to another.
Lymph nodes contain 2 types of white blood cells that fight invading micro-organisms:
- lymphocytes – attack viruses, bacteria and other micro-organisms
- macrophages – engulf and destroy foreign substances, damaged cells and bits of broken cells
Lymph nodes are located in groups in the following major locations:
- neck – cervical nodes
- chest (thoracic) cavity – thoracic and mediastinal nodes
- armpit – axillary nodes
- abdominal cavity – para-aortic (peri-aortic) and mesenteric nodes
- groin – inguinal nodes
The main functions of the lymph nodes are to:
- filter harmful particles, such as bacteria, viruses and foreign substances, from the lymph before returning it to the bloodstream
- activate the immune system
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 located in the upper-left abdomen. The spleen:
- makes, stores and removes lymphocytes
- filters the blood
- stores red blood cells
- destroys old red blood cells
Thymus
The thymus is located in the chest behind the breastbone (sternum). It is where T lymphocytes mature and multiply.
Tonsils
The tonsils are 2 small masses of lymphatic tissue in the throat that contain lymphocytes.
Adenoids
The adenoids are actually a single, small mass of lymphatic tissue in the back of the nose (nasopharynx) that contains lymphocytes. Although they are often called adenoids there is only one adenoid. The adenoid is also sometimes called the pharyngeal tonsil. The adenoids are present in infants and children, and start to shrink just before puberty. They are usually absent in adults.
Bone marrow
Bone marrow is soft, spongy tissue in the centre of certain bones. It contains immature blood cells called stem cells. Stem cells develop into:
- red blood cells – deliver oxygen to the body
- white blood cells (including lymphocytes) – protect the body from infection
- platelets – help blood to clot
Function
The main functions of the lymphatic system are to:
- move excess fluid from tissues and return it to the bloodstream
- help defend the body against disease
- provide an alternate route for transporting hormones, nutrients and waste products