What anatomical structure marks the boundary between the upper and lowerrespiratory systems?

The anatomical structure that marks the boundary between the upper and lower respiratory systems is the larynx. Here's a step-by-step explanation:

1. The respiratory system is divided into two main parts: the upper respiratory tract and the lower respiratory tract.

2. The upper respiratory tract includes the nose, nasal cavity, mouth, throat (pharynx), and voice box (larynx).

3. The lower respiratory tract includes the windpipe (trachea), bronchial tubes, and lungs.

4. The larynx, also known as the voice box, is the last component of the upper respiratory tract. It is located in the neck and is responsible for sound production (voice).

5. Below the larynx is the trachea, which marks the beginning of the lower respiratory tract. The trachea carries air from the larynx down into the lungs.

6. Therefore, the larynx serves as the boundary between the upper and lower respiratory systems.