The pharynx is divided into the nasopharynx, the oropharynx, and the hypopharynx. The nasopharynx lies above the soft palate and is posterior to the nasal cavities. On its postero-lateral wall is the opening of the eustachian tube. The adenoids are pharyngeal tonsils and hang from the posterosuperior wall near the opening of the eustachian tube. The oropharynx lies below the soft palate, behind the mouth, and superior to the hyoid bone. Posteriorly, it is bounded by the superior constrictor muscle and the cervical vertebrae. Below the oropharynx is the area known as the hypopharynx (or laryngopharynx). The hypopharynx is surrounded by three constrictor muscles, which are innervated by the glossopharyngeal and vagus nerves. The hypopharynx ends at the level of the cricoid cartilage, where it communicates with the esophagus through the upper esophageal sphincter. Figure 12-7 illustrates the functional parts of the pharynx.
The muscular walls of the pharynx are formed by the constrictor muscles, which function during the act of swallowing. The blood supply is derived from the external carotid artery.
Lymphatic tissue is abundant in the pharynx. The lymphoid tissue consists of the palatine tonsils, the adenoids, and the lingual tonsils. These tissues form Waldeyer's ring. The palatine tonsils lie in the tonsillar fossa, between the anterior and posterior pillars. The palatine tonsils are almond-shaped and vary considerably in size. The adenoids lie on the posterior wall of the nasopharynx, and the lingual tonsils are located at the base of the tongue. The upper portion of the pharynx drains to the retropharyngeal nodes, and the lower part drains to the deep cervical lymph nodes.
Figure 12-7 Functional parts of the pharynx.
The functions of the pharynx are as follows:
Swallowing, or deglutition, is divided into three stages. The voluntary stage occurs when a bolus of food is forced by the tongue past the tonsils to the posterior pharyngeal wall. The second stage is involuntary constriction by the pharyngeal muscles, propelling the bolus from the pharynx to the esophagus. The third stage is also involuntary, in which the esophageal muscles push the bolus down into the stomach. The larynx is first raised and then closed during the first two stages of swallowing. The eustachian tubes open during swallowing when the nasopharynx closes.
The pharynx also acts as a structure of resonation and articulation. Resonation refers to the vibration of a structure. Articulation is the change in shape of a structure to produce speech. Contracting the pharyngeal muscles causes a change in the acoustic quality of speech. Changes in the size and shape of the pharynx affect resonance. The soft palate affects resonance by opening and closing the partition between the oral and nasal cavities. If closure is incomplete, nasal speech results.
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