chambers of the nasal cavity to prevent damage to the lungs. The nasal and oral cavities are separated by the palate. The anterior, rigid portion is called the hard palate, and the posterior fleshy part is called the soft palate. The mouth and nose serve as secondary respiratory structures. Pharynx The pharynx, or throat, serves both the respiratory and digestive systems and aids in speech. It has a mucous membrane lining that traps microscopic particles in the air and aids in adjusting temperature and humidifying inspired (inhaled) air. The pharynx connects with the mouth and nasal chambers posteriorly. According to its location, the pharynx is referred to as the nasopharynx posterior to the nasal chambers), the oropharynx (posterior to the mouth), or the laryngopharynx (posterior to the pharynx). Epiglottis The epiglottis is a lidlike, cartilaginous structure that covers the entrance to the larynx and separates it from the pharynx. It acts as a trap door to deflect food particles and liquids from the entrance to the larynx and trachea. Larynx The larynx, or voice box, is a triangular cartilaginous structure located between the tongue and the trachea. It is protected anteriorly by the thyroid cartilage (commonly called the Adam's apple), which is usually larger and more prominent in men than in women. During the act of swallowing, it is pulled upward and forward toward the base of the tongue. The larynx is responsible for the production of vocal sound (voice). This sound production is accomplished by the passing of air over the vocal cords. The ensuing vibrations can be controlled to produce the sounds of speech or singing. The nose, mouth, throat, bone sinuses, and chest serve as resonating chambers to further refine and individualize the voice. Trachea The trachea, or windpipe, begins at the lower end of the larynx and terminates by dividing into the right and left bronchi. It is a long tube composed of 16 to 20 C-shaped cartilaginous rings, embedded in a fibrous membrane, that support its walls, preventing their collapse (fig. 1-39). The trachea has a ciliated mucous membrane lining that entraps dust and foreign material. It also propels secretions and exudates from the lungs to the pharynx, where they can be expectorated. Bronchi The bronchi are the terminal branches of the trachea, which carry air to each lung and further divide into the bronchioles. Bronchioles The bronchioles are much smaller than the bronchi and lack supporting rings of cartilage. They terminate at the alveoli (fig. 1-40). Alveoli The alveoli are thin, microscopic air sacs within the lungs (fig. 1-40). They are in direct contact with the pulmonary capillaries. It is here that fresh oxygen exchanges with carbon dioxide by means of a diffusion process through the alveolar and capillary cell walls 1-34 HM3F0139 NOSTRIL SINUS NASAL CAVITY HARD PALATE SOFT PALATE PHARYNX LARYNX BRONCHUS RIGHT LUNG LEFT LUNG EPIGLOTTIS TRACHEA ORAL CAVITY Figure 1-39.—Organs of the respiratory system.