The pharynx (far′ ingks; throat) is the common passageway for both the respiratory and the digestive systems. Air from the nasal cavity and air, food, and water from the mouth pass through the pharynx. Inferiorly, the pharynx leads to the rest of the respiratory system through the opening into the larynx and to the digestive system through the esophagus. The pharynx can be divided into three regions: the nasopharynx, the oropharynx, and the laryngo-pharynx (figure 15.2a).
The nasopharynx (nā′ zō-far′ ingks) is the superior part of the pharynx. It is located posterior to the choanae and superior to the soft palate, which is an incomplete muscle and connective tissue partition separating the nasopharynx from the oropharynx. The uvula (ū′ vū-lă; a little grape) is the posterior extension of the soft palate. The soft palate forms the floor of the nasopharynx. The nasopharynx is lined with pseudostratified ciliated columnar epithelium that is continuous with the nasal cavity. The auditory tubes extend from the middle ears and open into the nasopharynx. The posterior part of the nasopharynx contains the pharyngeal (fă-rin′ jē-ăl) tonsil, which helps defend the body against infection . The soft palate is elevated during swallowing; this movement closes the nasopharynx and prevents food from passing from the oral cavity into the nasopharynx.
The oropharynx (ōr′ ō-far′ ingks) extends from the uvula to the epiglottis, and the oral cavity opens into the oropharynx. Thus, food drink, and air all pass through the oropharynx. The oropharynx is lined with stratified squamous epithelium, which protects against abrasion. Two sets of tonsils, the palatine tonsils and the lingual ton-sil, are located near the opening between the mouth and the orophar-ynx. The palatine (pal′ ă-tı̄n) tonsils are located in the lateral walls near the border of the oral cavity and the oropharynx. The lingualtonsil is located on the surface of the posterior part of the tongue.
The laryngopharynx (lă-ring′ gō-far-ingks) passes posterior to the larynx and extends from the tip of the epiglottis to the esophagus. Food and drink pass through the laryngopharynx to the esophagus. A small amount of air is usually swallowed with the food and drink. Swallowing too much air can cause excess gas in the stomach and may result in belching. The laryngopharynx is lined with stratified squamous epithelium and ciliated columnar epithelium.