Which part is NOT part of the respiratory system?

The esophagus is the structure that is not part of the respiratory system. Its primary function is to serve as a conduit for food and liquids from the mouth to the stomach, playing a critical role in the digestive system rather than the respiratory process.

In contrast, the pharynx, trachea, and alveoli are all integral components of the respiratory system. The pharynx is a muscular tube that connects the nasal cavity and mouth to the larynx and esophagus, facilitating not only breathing but also swallowing. The trachea, commonly known as the windpipe, is a tubular structure that provides a clear airway for air to enter and exit the lungs. The alveoli are tiny air sacs within the lungs where gas exchange occurs, allowing oxygen to enter the bloodstream and carbon dioxide to be expelled.

Recognizing the distinct functions of these structures helps clarify the boundaries of the respiratory system, distinguishing it from the digestive system where the esophagus is located.