Lymph node - function, definition
A small structure of lymphatic tissue. LYMPH nodes, sometimes erroneously called lymph glands, occur individually as well as in beadlike strings within the tissues. The lymph nodes range in size from that of a grain of rice to that of a kidney bean, and appear roughly kidney shaped.
Each lymph node contains high numbers of lymphocytes and macrophages (tissue-resident monocytes), which filter pathogens and cellular debris from the lymph. Follicles within the lymph node contain B-cells and T-cells, which proliferate and mature in the follicles. The B-cells produce antibodies specific to the antigens the lymph carries into the lymph node. The lymph node adds these antibodies to the lymph as the lymph exits the node. The lymph node’s follicles release additional T-cells as necessary to fight INFECTION, responding to chemicals PHAGOCYTOSIS releases. Extensive networks of lymphatic capillaries carry lymph among the lymph nodes as well as to and from the larger LYMPH VESSELS.
Lymph nodes commonly swell when they are actively responding to infection because they fill with the pathogenic cells they filter from the lymph, a circumstance doctors call LYMPHADENOPATHY. LYMPHADENITIS occurs when the infection involves the lymph node itself. The lymph nodes also can become seeding sites for cancer cells that are metastasizing (spreading) to other parts of the body. Most operations to remove cancerous tumors also include removal of adjacent lymph nodes to examine them for the presence of cancer cells, which is key to the STAGING AND GRADING OF CANCER.