Lymphatic system

A system of vessels (lymphatic vessels) that drains lymph from tissues all over the body back into the bloodstream. The lymphatic system is part of the immune system and has a major function in defending the body against infection and cancer. This system also plays a part in the absorption of fats from the intestine. All body tissues are bathed in lymph, a watery fluid derived from the bloodstream. Much of this fluid is returned to the bloodstream through the walls of the capillaries (see circulatory system), but the remainder is transported to the heart through the lymphatic system. Lymph is moved along the lymphatic vessels during physical activity, as muscle contractions compress the vessels; valves inside the vessels ensure that the lymph flows in the correct direction. Situated on the lymphatic vessels are lymph nodes, through which the lymph passes. These nodes filter the lymph and trap infectious microorganisms or other foreign bodies. The nodes contain many lymphocytes, white blood cells that can neutralize or destroy invading bacteria and viruses. The lymphatic system also includes the spleen and the thymus, which produce lymphocytes.