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A chamber at the oral end of the vertebrate alimentary canal, leading to the esophagus. In adult humans it is divided anteriorly by the soft palate into a nasopharynx and an oropharynx, lying behind the tongue but anterior to the epiglottis; there is also a retropharyngeal compartment, posterior to both epiglottis and soft palate. The nasopharynx receives the nasal passages and communicates with the two middle ears through auditory tubes. The retropharynx leads to the esophagus and to the larynx, and the paths of breathing and swallowing cross within it. See Esophagus, Larynx
in all chordates and man, the entoderm-lined portion of the foregut behind the oral cavity in which the gill slits develop.
In anamniotic chordates the gill slits open to the exterior; water passes through them and washes over the gills. In lower chordates the number of gill slits varies from two (for example, in Salpa and Appendicularia) to several hundred (for example, in Ascidia). Lower chordates that feed passively (that is, that receive food with the current of water, such as tunicates and lancelets) have a special pharyngeal apparatus for capturing food particles—the endostyle, a groove on the ventral side of the pharynx that is lined with ciliated epithelium containing muciparous adenoblasts. Food particles adhere to the mucus and are transported to the intestine by the undulating epithelial cilia. Among the vertebrates only the larvae of lampreys (ammocoetes) have an endostyle. In vertebrates the pharynx is supplied with powerful striated muscle and innervated by the glossopharyngeal and vagus nerves. Five to 17 pairs of gill slits develop in the walls of the pharynx of Agnatha, and five to eight pairs in fishes. The rudiments of gill slits—the saclike beginnings of the branchial pouches—can be found in the embryos of all terrestrial vertebrates. The lungs develop from the terminal pair of gill pouches. The thymus and thyroid glands, and in terrestrial vertebrates the parathyroid gland as well, are derivatives of the pharyngeal epithelium. In fishes the pharynx leads to the esophagus. In terrestrial vertebrates, with the development of pulmonary respiration and the formation of a middle ear, the esophagus, larynx, and eustachean tubes have separate openings into the pharynx. In addition, in connection with the formation of a hard and soft palate, internal nares (choanae), which in amphibians and most reptiles and birds open into the oral cavity, in mammals open into the upper, so-called nasopharyngeal, section of the pharynx. The opening of the pharynx into the oral cavity in mammals is called the mouth. The mouth is bounded above by the soft palate, below by the radix linguae, and laterally by two pairs of palatine arches, between which lie large lymph nodes— the tonsils.
In invertebrates the pharynx is an isolated muscular section of the foregut, joining the mouth (sometimes the oral cavity) with the esophagus. It is lined (in contrast to that of the chordates) with epithelial cells of ectodermal origin.
A. N. DRUZHININ
The pharynx in man is the first section of the gastrointestinal tract, which joins the oral cavity with the esophagus. It performs functions of swallowing and breathing. The pharynx is located behind the nasal and oral cavities and communicates below with the larynx and, through the eustachean (auditory) tubes, with the right and left tympanic cavities. It consists of a funnel-shaped muscular pouch, extending from the base of the skull to the seventh cervical vertebra, where it passes into the esophagus. The length of the pharynx in the adult is approximately 12 cm and its maximum width, 5 cm. The pharynx is divided into three sections—the upper section, or nasopharynx, which serves only for respiration; the middle section, or oropharynx; and the laryngeal section. The pharynx is lined interiorly with mucous membrane, which in turn is covered with a fibrous membrane. The muscular sheath is divided into an inner layer of longitudinal muscles (which raise the pharynx) and an outer layer of circular muscles (which constrict the pharynx). The connective-tissue adventitia lies over the muscle layer. The pharynx is innervated by branches of the glossopharyngeal, vagus, and sympathetic nerves, which constitute the pharyngeal plexus. The pharynx receives a rich blood supply from branches of the external carotid arteries. Blood drains principally into the internal jugular vein system, and lymph, into the postpharyngeal and superior deep cervical nodes.
V. V. KUPRIIANOV