Bone marrow is the soft tissue in the center of all the bones in the body. It produces both red and white blood cells. The white blood cells created in the bone marrow can be further divided into two types: lymphocytes and phagocytes. These two types of white blood cells are the immune system's front-line fighters. The bone marrow also houses the lymphocytes known as B-cells until they reach maturity. B-cells fight disease by secreting antibodies into the body fluid. These antibodies fight bacteria and viruses.

Thymus

The thymus is located near the top of the lungs and behind the breast bone. It is a key to immune response. Lymphocytes known as T-cells get their name from the thymus, because after the bone marrow produces them they are passed on to the thymus, which fosters their development. T-cells both regulate immune response and attack infected or malignant body cells. The thymus also acts as the central clearing house of immune response, passing lymphocytes into the lymphatic system, which transports them to where they are needed.

Lymphatic vessels

The lymphatic vessels are the arteries that carry white blood cells throughout the body. White cells also can travel in the blood, but the lymphatic vessels are better equipped to transport the waste materials that the white blood cells pick up. Like small creeks that empty into larger and larger rivers, the lymphatic vessels feed into larger and larger channels. At the base of the neck they merge and their contents are discharged into the blood stream, which carries the waste to the kidneys for processing and removal from the body.

Lymph nodes and spleen

Lymph nodes are small, bean-shaped stopping points that are spread throughout the body. They are "wait stations" for white blood cells to congregate until they are needed to fight an invading pathogen. Clumps of lymphoid tissue are found in most parts of the body, especially in the linings of the digestive tract and the airways and lungs-all the places where pathogens can enter the body. These lymphatic tissues include the tonsils, adenoids, and appendix. The spleen also contains special compartments where white blood cells gather and work.

All told, the lymphatic system is composed of literally hundreds of miles of lymphatic vessels and lymph nodes. It is key to the elimination of waste products generated throughout the body. Dead cells, one of the major components of this waste, collect in the lymph nodes, where they are passed on to the blood stream, which in turn delivers them to the lungs, kidneys, colon, and skin for elimination from the body. Together, all of the organs that make up the lymphatic system work to protect us from disease and illness.