Final answer:
When breathing through the mouth, air passes through the oropharynx and then the nasopharynx, which are parts of the pharynx. The pharynx facilitates both respiration and digestion, and has adaptations like the epiglottis to manage the passage of air and food without choking.
Step-by-step explanation:
If you breathe through your mouth, air passes through the oropharynx and nasopharynx. The pharynx is a tubular organ that serves as a pathway for both air and food, connecting the mouth and nasal cavity with the larynx and esophagus. The pharynx has three subdivisions: the nasopharynx, oropharynx, and laryngopharynx.
The nasopharynx is the uppermost region, located behind the nasal cavities and is involved in breathing and speech. Beneath it is the oropharynx, which lies behind the oral cavity and extends to the laryngopharynx. The oropharynx serves as a common passageway for both air and food. When breathing through the mouth, air enters the oropharynx directly after passing the oral cavity. It then travels through the nasopharynx, although no air exchange occurs here if the nasal cavities are bypassed.
During swallowing, the pharynx gives priority to food over air, with involuntary muscle contractions closing off the air passageways to prevent choking. The epiglottis, a flap of connective tissue, also closes over the larynx during swallowing to ensure that food enters the esophagus and not the airways.