[Lymphatic system and its significance in immune processes]

Up to 80-90th of XX century, lymphatic system was considered as a part of vascular system, performing the functions of drainage of tissue fluid from the organs, in addition to the venous system. In the second half of XX century, detailed research of the organs of lymphatic system, and of lymph nodes in particular, lead to the understanding of a defensive role of this system, which participated in the elimination of foreign (potentially dangerous) particles--fragments of dead cells and other tissue elements. Tissue fluid containing these substances, is absorbed into lymphatic capillaries (where it gains the name of lymph), flows through the lymphatic vessels to the lymph nodes, which serve as lymph biological filters. In the lymph nodes, the foreign particles are detained on the fibers of the reticular meshwork, where they are recognized by lymphocytes and are eliminated with the help of macrophages. After passage through the lymph nodes, cleared lymph flows into the blood through lymphatic ducts and trunks, which are continuous with the large veins in the lower regions of the neck. Thus, the lymph nodes, that are the organs of immune system, which are formed by lymphoid tissue and possess special structures for the clearance of lymph (tissue fluid), are, at the same time, the organs of lymphatic system. Lymphatic capillaries and vessels provide the transport of the lymph (tissue fluid) to the lymph nodes and conduct the lymph to the blood.