Functionally, the respiratory system structures are separated into the conducting zone and respiratory zone. The conducting zone consists of the nose, pharynx, larynx, trachea, bronchi, and bronchioles. These structures form a continuous passageway through which air can move in and out of the lungs. The second functional division of the respiratory system is found deep inside the lungs and is called the respiratory zone. It is made up of the respiratory bronchioles, alveolar ducts, and alveoli. These thin-walled structures form a region where inhaled oxygen (O2) can be exchanged for carbon dioxide (CO2) in nearby capillaries.
Anatomically, these same structures are often divided into the upper and lower respiratory tracts. The upper respiratory tract is formed by the nose, pharynx, and larynx, which are located in the head and neck. The lower respiratory tract is formed by the trachea, bronchi, and lungs (= bronchioles, alveolar ducts, and alveoli), which are located in the thorax (chest).
