Which of the following is part of the lower airway?

The trachea is considered part of the lower airway because it serves as the primary passage for air to travel into the lungs. It begins at the lower part of the larynx and extends down into the thoracic cavity, where it divides into the right and left bronchi, leading to each lung. The lower airway includes structures that are involved in the conduction of air into the lungs, where gas exchange takes place.

In contrast, the larynx, while integral to the airway system, is categorized as part of the upper airway because it is located above the trachea and plays a role in voice production and protecting the airway during swallowing. The nose is also part of the upper airway, responsible for filtering, humidifying, and warming the air before it enters the lower airway. The epiglottis, which is a flap of tissue, prevents food and liquid from entering the trachea during swallowing, and while it is crucial for airway protection, it is still considered part of the upper airway anatomy.