The lymphatic circulation is an important auxiliary part of the circulatory system and can be viewed as complementary to the (blood) circulatory system. All lymphatic vessels converge to form the two largest lymphatic ducts in the body, the thoracic duct on the left and the right lymphatic duct on the right, which enter the left and right subclavian veins, respectively. The thoracic duct collects lymph from the left upper and lower body, accounting for about 3/4 of the total body lymph volume, while the right lymphatic duct is formed by the right cervical lymphatic trunk, the right subclavian lymphatic trunk, and the right bronchiolomediastinal lymphatic trunk, and collects lymph from the right upper body, accounting for about 1/4 of the total body lymph volume. An important feature of the lymphatic circulation is unidirectional flow without forming a true circulation. Tissue fluid through the capillary lymphatic vessels into the lymphatic system and the formation of the circulation, for the transport of substances, cell metabolism, the human body has an important role in defense. 1. Transportation of substances, cell metabolism: the lymphatic circulation is very important for the normal activities of the body, can recycle the body’s proteins, but also transport fats, regulate the fluid balance between plasma and tissue fluids, can be cleared of erythrocytes, bacteria in the tissues, lymphocytes can also produce immune response. 2. The lymphatic circulatory system is the body’s defense system. When the human body is invaded by viruses or bacteria, it will produce immune function and the lymph nodes in the corresponding areas will be enlarged. The enlarged lymph nodes are the normal immune response to the invading viruses. Lymphatic circulation plays an important role in the body’s resistance to external bacterial and viral invasion.