Lymphatic Circulatory System
Leukocytes and their products use two circulatory systems: cardiovascular system and the lymphatic circulatory system. The cardiovascular system is responsible for circulation of blood throughout the body. Peripheral blood is “filtered” by the spleen and liver. Organisms and antigens that enter directly into the systemic circulation are trapped in these two organs, of which the spleen plays the most important role as a lymphoid organ. The lymphatic circulatory system, on the other hand, is an extensive capillary network that collects lymph, a clear watery fluid containing leukocytes and cellular debris, from various organs and tissues.
Cleared lymph originating from below the diaphragm and the upper left half of the body drains via efferent lymphatics into the thoracic duct for subsequent drainage into the left innominate vein. Cleared lymph originating from the right side above the diaphragm drains into the right lymphatic duct, which subsequently drains into the origin of the right innominate vein. The same routes are followed by the lympho-cytes stimulated and produced in the lymph nodes, or periph-eral lymphoid tissues, which eventually reach the systemic circulation.