Once lymph fluid reaches the lymph nodes, it is filtered and treated. The lymphatic system is part of the body's immune system and foreign cells that arrive in the lymph nodes are attacked by immune system cells. After the lymph fluid is concentrated within the lymph nodes, it is filtered into the bloodstream where the kidneys capture the waste material and pass it over to the bladder. You can see your lymphatic system working when you see swelling go down around an injury.