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.