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Functionally, the respiratory system is separated into a conducting zone and respiratory zone.

The conducting zone consists of the nose, pharynx, larynx, trachea, bronchi, and bronchioles. These structures form a continuous passageway for air to move in and out of the lungs.

The respiratory zone is found deep inside the lungs and is made up of the respiratory bronchioles, alveolar ducts, and alveoli. These thin-walled structures allow inhaled oxygen (O2) to diffuse into the lung capillaries in exchange for carbon dioxide (CO2).

Anatomically, the same structures are often divided into the upper and lower respiratory tracts.

The upper tract structures are found in the head and neck and consist of the nose, pharynx, and larynx.

The lower tract structures are found in the thorax or chest and include the trachea, bronchi, and lungs (= bronchioles, alveolar ducts, and alveoli).

*Please note that many authorities include the larynx with the lower respiratory tract structures.

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Respiratory System Zones & Divisions