A Lymph node (pronounced /ˈlɪmf noʊd/) is an organ consisting of many types of cells, and is a part of the lymphatic system. Lymph nodes are found all through the body, and act as filters or traps for foreign particles. They contain white blood cells that use oxygen to process. Thus they are important in the proper functioning of the immune system.

Lymph nodes also have clinical significance. They become inflamed or enlarged in various conditions, which may range from trivial, such as a throat infection, to life-threatening such as cancers. In the latter, the condition of lymph nodes is so significant that it is used for cancer staging, which decides the treatment to be employed, and for determining the prognosis.

Lymph nodes can also be diagnosed by biopsy whenever they are inflamed. Certain diseases affect lymph nodes with characteristic consistency and location.

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