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Hodgkin lymphoma

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Anatomy and physiology of the lymphatic system

Hodgkin lymphoma (HL) is a type of cancer that starts in the lymphatic system. The lymphatic system works with the circulatory system and the immune systemimmune systemThe complex group of cells and organs that defend the body against infection, disease and foreign substances. – 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 cellswhite blood cellsA type of blood cell that helps the body fight infection and diseases. (lymphocyteslymphocytesA type of white blood cell that fights viruses, bacteria, foreign substances or abnormal cells (including cancer cells).), antibodiesantibodiesA type of protein made by the immune system that disarms or destroys a specific foreign substance (antigen) when it appears in the body. 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  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 (nasopharynxnasopharynxThe upper part of the pharynx (throat) behind the nose and above the soft palate (the back, soft part of the roof of the mouth).) 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 cellsred blood cellsA type of blood cell that carries oxygen to and carbon dioxide from tissues in the body. Red blood cells contain hemoglobin (a protein that carries oxygen and gives blood its red colour) and are made in the bone marrow. – deliver oxygen to the body
  • white blood cells (including lymphocytes) – protect the body from infection
  • plateletsplateletsA type of blood cell that helps blood to clot. Platelets are made in the bone marrow. – 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

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