The lymphatic system is made up of lymphatic vessels, lymphatic tissues and lymphatic organs. Lymphatic organs in turn include lymph nodes, thymus, spleen and tonsils. Lymph is the lymphatic fluid (tissue fluid that enters the lymphatic vessels) contained in the lymphatic sinuses of the lymphatic tracts and lymph nodes. A lymph node is a small grayish-red body of varying size, round or oval in shape, which is bulging on one side and depressed on the other. Lymph nodes are mostly distributed in groups and their number is not constant, there are about 400 to 450 lymph nodes in young people. Its main function is to filter lymph, produce lymphocytes and carry out immune response, and it plays an important role in lymphatic drainage.