Lymphatic System Learning Path

Overall role of lymphatic system

The lymphatic system is an organ system in vertebrates that complements the circulatory system and supports immune function. It is made up of lymphatic vessels, lymph nodes, lymphoid organs and tissues, and circulating lymph. Unlike the circulatory system (a closed system), the lymphatic system is open: lymph originates from interstitial fluid that leaks from blood capillaries into tissues, then drains into lymphatic vessels. This provides an accessory return route to the bloodstream for the fluid that is not reabsorbed directly by blood vessels. A major role of the lymphatic system is immune defense. Lymph is similar to blood plasma and contains waste products, cellular debris, bacteria, and proteins, with lymphocytes being the main immune cells. Lymphoid organs and tissues are sites where lymphocytes are produced, mature, and/or become activated. Lymph passes through lymph nodes, where it is filtered to remove unwanted materials such as bacteria and damaged cells, before draining into larger lymph ducts (right lymphatic duct and thoracic duct) that return lymph to the venous circulation. Lymph is moved through the system by muscle contractions, and in some vertebrates a lymph heart may help pump lymph toward the veins.

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Lymph formation from interstitial fluid

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