The respiratory system, functionally, can be separated in two zones namely the conducting zone (nose to bronchioles) form a path for conduction of the inhaled gases and respiratory zone (alveolar duct to alveoli) where the gas exchange takes place. Anatomically, respiratory tract is divided into upper (organ outside thorax-nose,pharynx and larynx) and lower respiratory tract (organ within thorax-trachea, bronchi, bronchioles, alveolar duct and alveoli). Airway closure is a normal phenomenon in the body, with reopening of airways during the succeeding inspiration.
The appropriate choice would be the supraglottic portion of the laryngeal vestibule. It is the portion of the cavity of the larynx above the vocal cords. It is wide and triangular in shape, it is inlet to another cavity in the lateral wall of larynx, the laryngeal ventricle.
