The conducting zone of the respiratory tract has passageways that carry air to and from the exchange surfaces of the lungs. The airways filter, warm, and moisten the air. Hairs near the entrance to the nasal cavity (the nares) filter out large particles. Highly vascularized nasal passages warm the air and mucous membranes lining the nasal cavity moisten the air.
The upper respiratory system extends from nares to pharynx. The external nares are the nostrils. The nasal cavity is the open space above the hard palate of the mouth. It detects odors, modifies speech, warms and moistens the air. Around the nasal cavity are the paranasal sinuses. These are air-filled spaces in the bones of skull (frontal, sphenoid, ethmoid, maxillary).
The pharynx begins posterior to the nasal cavity and ends at the larynx. It is divided into three parts: nasopharynx, oropharynx, and laryngopharynx. The nasopharynx is behind the nasal cavity. The oropharynx is behind the oral cavity and is a passageway for air and food. The laryngopharynx connects the pharynx to the larynx.
Making a Difference in the World 