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The lymph system is a network of organs, lymph nodes, lymph ducts, and lymph vessels that make and move lymph from tissues to the bloodstream. The lymph system is a major part of the body's immune system.
Lymph is a clear-to-white fluid made of:
Lymph nodes are soft, small, round- or bean-shaped structures. They usually cannot be seen or easily felt. They are located in clusters in various parts of the body, such as the neck, armpit, groin, and inside the center of the chest and abdomen.
Lymph nodes make immune cells that help the body fight infection. They also filter the lymph fluid and remove foreign material such as bacteria and cancer cells. When bacteria are recognized in the lymph fluid, the lymph nodes make more infection-fighting white blood cells, which causes the nodes to swell. The swollen nodes are sometimes felt in the neck, under the arms, and groin.
The lymphatic system includes the tonsils, adenoids, spleen, and thymus.
Armitage JO. Approach to the patient with lymphadenopathy and splenomegaly. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed .Philadelphia, PA: Saunders Elsevier; 2011:chap 171.