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The lymphatic system

The lymphatic system is a circulatory system made up of lymph vessels, which are much like blood vessels. It drains extra fluid (called lymph) that has passed out of the blood and into tissues and returns it back to the blood. The lymphatic system also includes tissues and organs that make, store and release lymphocytes (a type of white blood cell). These tissues and organs (called lymphatic or lymphoid tissue) also monitor the lymph for germs, foreign substances and abnormal cells and remove waste products and bacteria from the lymph.

The lymphatic system includes the tonsils, spleen, thymus, lymph nodes and lymph vessels and is an important part of the immune system that helps defend the body against disease. It also helps maintain blood pressure and transports some hormones, nutrients and waste products.

Diagram of the lymphatic system

Lymph

Lymph is a clear fluid that contains lymphocytes, a type of white blood cell that fights germs, foreign substances and abnormal cells, like cancer cells. Lymph also has macrophages, another type of white blood cell that helps fight infection. Lymph collects some waste products, bacteria and damaged cells from inside the body’s tissues so that they can be removed from the body or destroyed. Lymph drains into lymph vessels that carry it to lymph nodes. Lymph nodes clean the lymph and add more lymphocytes to it.

Lymphocytes

Lymphocytes fight disease and micro-organisms that cause infections, like bacteria, viruses, fungi and parasites. They are important cells in the body’s immune system. There are 3 types of lymphocytes:

  • B cells (B lymphocytes) make antibodies to fight an infection.
  • T cells (T lymphocytes) defend the body against disease and infection and control the immune response.
  • Natural killer cells attack cells infected with a virus and abnormal cells, like cancer cells.

Lymph vessels

Lymph vessels are tubes that carry lymph through the body to lymph nodes and back to veins. The network of lymph vessels is similar to blood vessels (arteries and veins) that carry blood. Lymph vessels carry waste products, germs and damaged cells away from the body’s tissues.

Lymph nodes

Lymph nodes are small, bean-shaped masses of lymphatic tissue along lymph vessels. They store lymphocytes and filter waste, bacteria and damaged cells (including cancer cells) from lymph. The lymphocytes inside the lymph nodes also attack bacteria and viruses that they find in the lymph. This is why lymph nodes often get swollen when we are sick or fighting off an illness like a cold or the flu.

Lymph nodes are found in many parts of 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:

  • 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)

Tonsils

Tonsils are small masses of tissue at the back of the mouth and nose and at the top of the throat. Tonsils have many lymphocytes.

The adenoid (pharyngeal tonsil) is a single, small mass of lymphatic tissue in the back of the nose that contains lymphocytes. The adenoid is largest in children and starts to shrink just before puberty. Although it is often called “the adenoids,” there is only one adenoid.

The tonsils and adenoid help the body fight infection and protect the opening to the digestive system and lungs from bacteria and viruses.

Spleen

The spleen is an organ in the abdomen, under the ribs on the left side of the body. It stores lymphocytes, filters the blood and destroys old blood cells. As blood passes through the spleen, lymphocytes attack any bacteria or virus or other types of harmful substances that can cause infection or illness.

Thymus

The thymus is a gland in the middle of the chest behind the sternum (breastbone) that sits in an area of the chest called the mediastinum. T cells (a type of lymphocyte) mature inside the thymus. But the T cells in the thymus don’t respond to infection until they are released into the blood and the lymphatic system. The thymus starts to shrink during late childhood and adolescence, becoming very small in adults.

Lymphatic tissue

The lymphatic system also includes areas of the body that have high numbers of lymphocytes. These areas are called lymphatic tissue. They include the appendix and areas of the small intestine called Peyer’s patches. There are also areas of lymphatic tissue scattered in other parts of the digestive system and respiratory system. Like lymph nodes, lymphatic tissue helps remove waste, bacteria and damaged cells from lymph.

Bone marrow

The bone marrow is where lymphocytes and other blood cells are made. The bone marrow is the soft, spongy area inside of most bones. Many of the blood cells in the bone marrow are immature and are called stem cells. Stem cells change and grow into different types of cells, including blood cells. Most blood cells grow and mature in the bone marrow. Most blood cells leave the bone marrow and move into the blood and other areas of the body once they are mature.

white blood cell (WBC)

A type of blood cell that helps the body fight infection and diseases.

White blood cells are made in the bone marrow and are found in the blood and lymphatic tissue. They play an important role in immune response (the immune system’s reaction to the presence of foreign substances in the body).

Also called leukocyte.

hormone

A substance that regulates specific body functions, such as metabolism, growth and reproduction.

Natural hormones are produced by glands. Artificial or synthetic hormones can be made in the lab.

macrophage

A type of white blood cell that helps fight infection by surrounding and killing foreign cells or micro-organisms, removing dead cells and stimulating other immune system cells. 

Macrophages develop from monocytes that have moved from the blood into tissues.

Macrophages are a type of phagocyte (a white blood cell that surrounds and kills bacteria or micro-organisms, eats foreign material, removes old or damaged cells and helps to boost the immune system).

abdomen

The part of the body between the chest and the pelvis that contains the digestive system and other organs.

Abdominal means referring to or having to do with the abdomen, as in abdominal wall.

Commonly called the belly.

mediastinum

The space in the chest between the lungs, breastbone and spine that contains the heart, great blood vessels, thymus, trachea (windpipe), esophagus and lymph nodes.

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