Organ system involved in respiration .
In humans, the diaphragm and, to a lesser extent, the muscles between the ribs generate a pumping action, moving air in and out of the lungs through a system of pipes (conducting airways), divided into upper and lower airway systems. The upper airway system comprises the nasal cavity (see nose ), sinus es, and pharynx ; the lower airway system consists of the larynx , trachea , bronchi, bronchioles, and alveolar ducts (see pulmonary alveolus ). The blood and cardiovascular system can be considered elements of a working respiratory system. See also thoracic cavity .