Lymph NodesLymph nodes are specialized masses of tissue that are situated along lymphatic system pathways. These structures filter lymph fluid before returning it to the blood. Lymph nodes, lymph vessels, and other lymphatic organs help to prevent fluid build-up in tissues, defend against infection, and maintain normal blood volume and pressure in the body. With the exception of the central nervous system (CNS), lymph nodes may be found in every area of the body.
Lymph Node FunctionLymph nodes serve two major functions in the body. They filter lymph and assist the immune system in building an immune response. Lymph is a clear fluid that comes from blood plasma that exits blood vessels at capillary beds. This fluid becomes the interstitial fluid that surrounds cells. Lymph vessels collect and direct interstitial fluid toward lymph nodes. Lymph nodes house lymphocytes which are immune system cells that originate from bone marrow stem cells. B-cells and T-cells are lymphocytes found in lymph nodes and lymph tissues. When B-cell lymphocytes become activated due to the presence of a particular antigen, they create antibodies that are specific to that specific antigen. The antigen is tagged as an intruder and labeled for destruction by other immune cells. T-cell lymphocytes are responsible for cell mediated immunity and participate in the destruction of pathogens as well. Lymph nodes filter lymph of harmful pathogens such as bacteria and viruses. The nodes also filter out cellular waste, dead cells, and cancerous cells. The filtered lymph from all areas of the body is eventually returned to the blood through a blood vessel near the heart. Returning this fluid to the blood prevents edema or the excess accumulation of fluid around tissues. In cases of infection, lymph nodes release lymphocytes into the blood stream to aid in the identification and destruction of pathogens.
Lymph Node StructureLymph nodes are situated deep within tissues and also in superficial clusters that drain specific areas of the body. Large clusters of lymph nodes located near the surface of the skin are found in the inguinal (groin) area, axillary (arm pit) area, and cervical (neck) area of the body. Lymph nodes appear to be oval or bean-shaped and are surrounded by connective tissue. This thick tissue forms the capsule or outer covering of the node. Internally, the node is divided into compartments called nodules. The nodules are where B-cell and T-cell lymphocytes are stored. Other infection fighting white blood cells called macrophages are stored in a central area of the node called the medulla. Enlarged lymph nodes are a sign of infection as B-cell and T-cell lymphocytes multiply in order to ward off infectious agents. Entering the larger curved outer area of the node are afferent lymphatic vessels. These vessels direct lymph toward the lymph node. As the lymph enters the node, spaces or channels called sinuses collect and carry lymph toward an area called the hilum. The hilum is a concave area in a node that leads to an efferent lymphatic vessel. Efferent lymphatic vessels take lymph away from the lymph node. The filtered lymph is returned to blood circulation via the cardiovascular system.
Cancer In Lymph NodesLymphoma is the term used for cancer that begins in the lymphatic system. This type of cancer originates in the lymphocytes that inhabit lymph nodes and lymph tissues. Lymphomas are grouped into two main types: Hodgkin's lymphoma and Non-Hodgkin lymphoma (NHL). Hodgkin's lymphoma can develop in lymph tissue which is found almost everywhere in the body. Abnormal B-cell lymphocytes can become cancerous and develop into several types of Hodgkin's lymphomas. Most commonly, Hodgkin's lymphoma starts in lymph nodes in the upper body regions and spreads through lymph vessels to lymph nodes in other areas of the body. These cancer cells can eventually enter the blood and spread to organs such as the lungs and liver. There are several subtypes of Hodgkin's lymphoma and all types are malignant. Non-Hodgkin lymphoma is more common than Hodgkin's lymphoma. NHL can develop from cancerous B-cell or T-cell lymphocytes. There are many more subtypes of NHL than Hodgkin's lymphoma. While the causes of lymphoma are not fully known, there are some risk factors for the possible development of the disease. Some of these factors include advanced age, certain viral infections, acquiring conditions or diseases that compromise the immune system, toxic chemical exposure, and family history.
- SEER Training Modules, Lymphatic System. U. S. National Institutes of Health, National Cancer Institute. Accessed 29 May 2013 http://training.seer.cancer.gov/