The major passages and structures of the upper respiratory tract include the mouth, nose, nasal cavities, paranasal sinuses, pharynx, and larynx. Dr. Mansfield, can you tell us about this part of the respiratory system?
Absolutely, Dr. Green. Air enters the body through the nose and mouth when a person inhales. Structures within the nose and mouth filter the incoming air by trapping particles that would otherwise cause illness or irritation of the respiratory tract. Nasal hairs at the opening of the nostrils trap larger particles.
Smaller particles, such as pollen or smoke, are trapped by mucus secreted by a mucous membrane that lines the entire respiratory system. Hairlike structures called cilia move these particles out of the nose.
From the nose, inhaled air enters the nasal cavity. The tissue that lines the nasal cavity, called the nasal epithelium, moistens, warms, and further cleanses the inhaled air. Nasal turbinates, or nasal conchae, are fingerlike projections inside the nasal cavity that increase the surface area for warming and moistening inhaled air. The nasal septum is a partition made of cartilage and bone that separates the nasal cavity into the left and right nostrils.
The nasal cavity is surrounded by the air-filled chambers called paranasal sinuses. These sinuses are named for the bones in which they are located: frontal, maxillae, ethmoid, and sphenoid. The paranasal sinuses reduce the weight of the skull, produce mucus, and influence voice quality by acting as resonating chambers.
After the nasal cavity, inhaled air passes through the pharynx, or throat. The pharynx is a muscular, funnel-shaped tube that contains the tonsils and adenoids. The tonsils and adenoids release white blood cells that fight infection.
Finally, the larynx, or voice box, forms the entrance to the lower respiratory system. A leaf-shaped flap, called the epiglottis, keeps food and liquid from entering the larynx during swallowing. In order to produce sound to speak or sing, two pairs of strong connective tissue bands, called the vocal cords, close together, and air from the lungs passing between them causes them to vibrate.