Fig. 8

Anatomy of the lymphatic system. a The lymphatic system includes the primary and secondary lymphoid organs and lymphatic vessels, providing a one-way drainage route from all tissues back ultimately to the blood circulation via the great veins in the neck. In the primary lymphoid organs (bone marrow and thymus), immune cell production and maturation takes place, whereas secondary lymphoid organs (lymph nodes, spleen, and mucosa-associated lymphoid organs such as Peyer’s patch, tonsils, and adenoids) are the sites for lymphocyte activation; b The thoracic duct is responsible for the lymph drainage coming from most of the body with the exception of the right side of the head and neck, the right side of the thorax and the right upper limb where drain lymph primarily into the right lymphatic duct; c–e The spleen, the Peyer’s patch and lymph nodes are highly organized structures with segregated B-cell and T-cell zones to optimize the induction of adaptive immune responses; f The capillary lymphatics drain downstream into the collecting lymphatics. Capillary LECs are interconnected via discontinuous junctions allowing the fluid to enter the system passively. Collecting LECs present with continuous junctions. Collecting lymphatics differ from capillary lymphatics by possessing intraluminal valves, LSMCs and a continuous basement membrane. LSMCs lymphatic smooth muscle cells, LECs lymphatic endothelial cells, GC germinal center. Created with Adobe Illustrator