Final answer:
The bronchus is not found in the upper airway; it is part of the lower airway. The upper airway includes structures like the pharynx and larynx.
Step-by-step explanation:
The structure that is NOT found in the upper airway from the options provided is the bronchus. The upper airway consists of the nose (nasal cavity), mouth (oral cavity), pharynx, and larynx. The pharynx, or throat, is a tube-like structure that continues from the nasal and oral cavities to the larynx and esophagus. It has three subdivisions: the nasopharynx, oropharynx, and laryngopharynx, each involved in the processes of breathing and digestion. The larynx, also known as the voice box, is situated below the pharynx and connects to the trachea. It plays a key role in voice production and helps to regulate airflow. In contrast, the bronchus is part of the lower airway, which begins at the trachea and extends into the lungs.