10.1 Organs and structures of the respiratory system  (Page 2/55)

Divisions of the pharynx

The nasopharynx    is flanked by the conchae of the nasal cavity, and it serves only as an airway. At the top of the nasopharynx are the pharyngeal tonsils. A pharyngeal tonsil    , also called an adenoid, is a collection of tissue similar to a lymph node that lies at the top portion of the nasopharynx. The function of the pharyngeal tonsil is not well understood, but it contains a rich supply of lymphocytes (a type of WBC) and is covered with ciliated epithelium that traps and destroys invading pathogens that enter during inhalation. The pharyngeal tonsils are large in children, but interestingly, tend to regress with age and may even disappear. The uvula is a small bulbous, teardrop-shaped structure located at the apex of the soft palate. Both the uvula and soft palate move like a pendulum during swallowing, swinging upward to close off the nasopharynx to prevent ingested materials from entering the nasal cavity. In addition, auditory (Eustachian) tubes that connect to each middle ear cavity open into the nasopharynx. This connection is why colds often lead to ear infections.

The oropharynx    is a passageway for both air and food. It contains two distinct sets of tonsils, the palatine and lingual tonsils. Similar to the pharyngeal tonsil, the palatine and lingual tonsils are composed of lymphoid tissue, and trap and destroy pathogens entering the body through the oral or nasal cavities.

The laryngopharynx    continues the route for ingested material and air until its inferior end, where the digestive and respiratory systems split. To the front,the laryngopharynx opens into the larynx, whereas to the back, it enters the esophagus.

Larynx

The larynx    is a structure below the laryngopharynx that connects the pharynx to the trachea and helps regulate the volume of air that enters and leaves the lungs ( [link] ). The structure of the larynx is formed by several pieces of cartilage.

Larynx

The epiglottis    , attached to the thyroid cartilage, is a very flexible piece of elastic cartilage that covers the opening of the trachea (see [link] ). When in the “closed” position, the unattached end of the epiglottis rests on the glottis. The glottis    is composed of the vestibular folds, the true vocal cords, and the space between these folds ( [link] ). The inner edges of the true vocal cords are free, allowing oscillation to produce sound. The size of the membranous folds of the true vocal cords differs between individuals, producing voices with different pitch ranges. Folds in males tend to be larger than those in females, which create a deeper voice. The act of swallowing causes the pharynx and larynx to lift upward, allowing the pharynx to expand and the epiglottis of the larynx to swing downward, closing the opening to the trachea. These movements produce a larger area for food to pass through, while preventing food and beverages from entering the trachea.