Which organ is NOT part of the lower airway?

The epiglottis is correctly identified as not being part of the lower airway. The epiglottis is a flap-like structure located at the base of the tongue that functions primarily to prevent food and liquid from entering the airway during swallowing. It plays a critical role in protecting the airway by covering the trachea during the swallowing process, but it is located in the upper airway.

In contrast, the trachea, lungs, and diaphragm are all integral components of the lower airway. The trachea serves as the main airway passage that conducts air from the upper airway into the lungs. The lungs are the primary organs of respiration, responsible for gas exchange during breathing. The diaphragm, although it is a muscle and not an airway structure, is crucial for breathing as it contracts and relaxes to allow air to enter and exit the lungs. Thus, considering the specific definitions of the airway structures, it becomes clear why the epiglottis does not belong to the lower airway category.