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The medullary cord is a dense structure in the lymph node, and it is composed of lymphatic tissue. These cords are found within the lymph node's medulla, which is located in the center of the node. They function by producing antibodies that flow out of the lymph node via the lymph fluid. These cords also contain numerous macrophages, which clean the lymph fluid before it exits the node.
Medullary cord tissue makes up most of a lymph node's medulla. The cords are separated by medullary sinuses, which are spaces through which lymph fluid flows. The barrier between the cords and sinuses is not solid, however, so the cords project into the sinuses to interact with the lymph fluid that flows through them. While lymphatic fluid is in contact with the medullary cord, the cells in the cord will deposit antibodies and remove harmful materials. The fluid will then flow out of the lymph node to fight antigens that are found in the rest of the body.
Most cells found in a medullary cord are either plasma cells, B cells or macrophages. Plasma cells are white blood cells that produce large quantities of generalized antibodies, and B cells are a type of lymphocyte that produces antibodies against a specific antigen. Macrophages act as a filter for lymph fluid by identifying and removing particulate material that is contained in the fluid.
The medullary cords are part of the lymphoid system, which traps foreign particles and fights infection throughout the body. When the body encounters an infection, the immune response occurs primarily within the lymph node. Structures within the lymph node accumulate excess lymphatic fluid and become swollen, causing the entire gland to appear enlarged.
Infections that typically cause enlarged lymph nodes include abscesses, ear infections, tonsillitis, skin infections and colds. Tuberculosis, mononucleosis, gingivitis, mouth sores and sexually transmitted diseases also can cause enlarged lymph nodes. The lymph nodes might also swell when an individual has an autoimmune disease, leukemia, Hodgkin's disease or lymphoma.
The medullary cord is an essential component of the human immune system. In individuals who have chronic immune deficiency, such as the deficiency caused by the human immunodeficiency virus (HIV), the cords or other structures within the lymph node might not function properly. The medullary cord might not produce enough antibodies to fight off infection, or the B cells within the cord might not operate as they should. In such cases, an otherwise mild infection can result in a severe illness or even death.