: a system of organs functioning in respiration and consisting especially of the nose, nasal passages, nasopharynx, larynx, trachea, bronchi, and lungs—called also respiratory tract; see lower respiratory tract, upper respiratory tract
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 (seenose), sinuses, and pharynx; the lower airway system consists of the larynx, trachea, bronchi, bronchioles, and alveolar ducts (seepulmonary alveolus). The blood and cardiovascular system can be considered elements of a working respiratory system. See alsothoracic cavity.