Excretory System. The organ system that filters blood and removes nitrogenous wastes from the body in the form of urea or uric acid. In humans, the two kidneys are the vital organs of blood filtration. In humans, other important structures of the system are the ureters, the urinary bladder, and the urethra.espiratory System. The organ system responsible for the intake of oxygen and diffusion of that gas into the blood and the elimination of carbon dioxide from the body. Important structures of the system are the pharynx, larynx, trachea, bronchi, bronchioles, and lungs.