The primary function of the lymph nodes is to fight pathogens, as they are a key part of the immune system. They accomplish this by several means, including removing foreign particles from the body, creating anti-bodies, producing lymphocytes and housing cell-eating cells known as macrophages. They are spread throughout the body and are connected by channels known as lymph vessels.
Lymph nodes are very small and shaped like a bean. Although they are spread throughout the body, they are mainly located in the areas of the neck, armpit, groin and chest. The nodes are connected by the lymph vessels, which are pathways that carry lymph through the body. Lymph is responsible for recirculating protein and excess fluid as well as carrying bacteria to the lymph nodes to be destroyed.
Arguably the most important function of lymph nodes is the production of lymphocytes. Lymphocytes are specialized white cells of which there are three kinds: T cells, B cells and natural killer cells. All of these cells contribute to the immune system by attacking and destroying other cells and, in the case of the T and B cells, building further immunity by creating antibodies. The macrophages, the other cells that are in the nodes but not created by them, destroy bacteria by ingesting and dissolving it with enzymes, a process known as phagocytosis.
When disease hits, the lymph nodes can be a major indicator of the condition involved. If they are inflamed, the amount of B cells will increase, and they will swell. When this happens, it is generally a sign of an infection or other disease state.
The types of diseases that affect the lymph nodes vary in severity and symptoms. In the case of a minor infection, such as a throat infection, only the glands around the neck will usually swell. In more serious diseases, such as cancer, the swollen glands may be all over the body.
With regard to cancer, the lymph nodes can be an indicator not only of the presence of the disease, but also the severity. They are often used to stage cancer, which means they can indicate how much the cancer has invaded the body; this is usually given a rank from 1 to 4, with 4 being the most severe.
In addition to being indicators of disease in the body, the lymph nodes can also be the site of disease. Hodgkin's disease, a form of cancer, is one such example. With Hodgkin's, the nodes themselves are cancerous. As one of the symptoms of the disease is swollen lymph nodes, biopsy of the nodes is used to diagnose it and differentiate it from other possible causes.