A lymph node is a small ball-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as filters or traps for foreign particles. 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.
Pathogens, or germs, can set up infections anywhere in the body. However, lymphocytes, a type of white blood cell, will meet the antigens, or proteins, in the peripheral lymphoid organs, which includes lymph nodes. The antigens are displayed by specialized cells in the lymph nodes. Naive lymphocytes (meaning the cells have not encountered an antigen yet) enter the node from the bloodstream, through specialized capillary venules. After the lymphocytes specialize they will exit the lymph node through the efferent lymphatic vessel with the rest of the lymph. The lymphocytes continuously recirculate the peripheral lymphoid organs and the state of the lymph nodes depends on infection. During an infection, the lymph nodes can expand due to intense B-cell proliferation in the germinal centers, a condition commonly referred to as "swollen glands".
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