Final answer:
Observation of nasal discharge initiates an examination of the respiratory system, focusing on key structures like the nasal cavity, which, along with the oral cavity and pharynx, supports breathing.
Step-by-step explanation:
Observation of the nose for nasal discharge often begins the examination of the respiratory system. The nose serves as the major entrance and exit for this system, and is composed of two major sections: the external nose and the nasal cavity, or internal nose. These structures play vital roles in air filtration, temperature regulation, and humidifying inhaled air before it reaches the lungs. Additionally, the nasal cavity, along with the oral cavity and pharynx, allows you to breathe even when your nostrils are congested.
During a medical exam, inspection of the oral cavity and pharynx, prompted by the common directive to "open your mouth and say 'ah'," is not only for checking signs of infection, such as tonsillitis, but also serves as a means to test the functions of the cranial nerves associated with the oral cavity. The nasal cavity, in particular, is lined with hairs and mucus that trap particles, supported by cilia that push out trapped pathogens.