Human Anatomy - Kotsan I. Y. 2009

Splanchnology
Digestive System
Pharynx

The Pharynx is an unpaired organ located in the HEAD and Neck region, posterior to the nasal and oral cavities and the Larynx. The Functions of the pharynx are diverse. First, it plays a role in Respiration by conducting air from the Nasal cavity into the larynx and vice versa. Second, the pharynx is an essential component of the Digestive System, actively participating in the act of swallowing and conveying food from the Oral Cavity to the Esophagus. Third, acting as a resonator, the pharynx is vital for articulated speech production, particularly singing. Finally, air passes from the pharyngeal cavity through the auditory tube into the tympanic cavity, which helps maintain a partial pressure equal to that of the external environment.

The pharynx is a funnel-shaped tube, 12–14 cm long, oriented with its wide end directed upward and flattened in the anteroposterior direction. Superiorly, it attaches to the BONES OF THE cranial base; inferiorly, at the border between the VI and VII cervical vertebrae, it narrows and continues into the esophagus. In an adult human, the pharynx is twice the length of the oral cavity, whereas in a newborn, it is approximately equal in length.

The pharynx has superior, posterior, two lateral, and anterior walls. The superior wall, which is tightly fused with the Base of the Skull, is called the pharyngeal fornix (fornix pharyngis). The posterior wall lies against the anterior surface of the bodies of the cervical vertebrae, separated from them by the prevertebral Muscles and the prevertebral layer of the Cervical fascia. Between the posterior surface of the pharynx and the layer of the cervical fascia lies the retropharyngeal space (spatium retropharyngeum), filled with loose Connective Tissue containing retropharyngeal Lymph Nodes. On both sides of the pharynx are the neurovascular bundles of the neck and the adipose tissue of the lateral pharyngeal space (spatium lateropharyngeum). The retropharyngeal and lateral pharyngeal spaces communicate with each other; this combined region is termed the peripharyngeal space (spatium peripharyngeum). The presence of loose connective tissue in the peripharyngeal space allows the pharynx to move relative to the cervical vertebrae during swallowing and various Head movements. The anterior wall of the pharynx features openings through which the pharyngeal cavity communicates with the nasal, oral, and laryngeal cavities.

The pharyngeal cavity is conventionally divided into three parts: the superior nasal part, the middle oral part, and the inferior laryngeal part (Fig. 141).

The nasal part of the pharynx (pars nasalis pharyngis) is located at the level of the First and Second cervical vertebrae, posterior to the choanae, which connect the pharynx to the nasal cavity. On the inner surface of the nasopharynx, at the junction of its superior and posterior walls and in the region of the fornix, There is a small elevation formed by an accumulation of lymphoid tissue—the pharyngeal (adenoid) tonsil (tonsilla pharyngealis (adenoidea)). The pharyngeal tonsil is well developed in children, whereas in adults it becomes inconspicuous or disappears entirely. On the lateral walls of the nasal pharynx, posterior to the choanae and at the level of the posterior end of the Inferior nasal concha, the funnel-shaped pharyngeal opening of the auditory tube (ostium pharyngeum tubae auditivae) is visible. Posteriorly and superiorly, this opening is bounded by the torus tubarius. Anterior to this opening, between it and the soft palate (palatine velum), lies an accumulation of lymphoid tissue—the tubal tonsil (tonsilla tubaria). Thus, the three pharyngeal Tonsils (the adenoid and the two tubal tonsils) together with the three oral tonsils (the lingual and two palatine tonsils) form a nearly complete ring of lymphoid tissue around the entrance to the pharynx—the Waldeyer-Pirogov ring, which plays a crucial role in The Immune System by neutralizing microbes that constantly enter The Human Body from the external environment through the nasal and oral cavities.

The oral part of the pharynx (pars oralis pharyngis) extends from the palatine velum to the entrance of the larynx and is located at the level of the fauces, which connect it to the oral cavity. The digestive and respiratory pathways cross within the oral part of the pharynx.

The laryngeal part of the pharynx (pars laryngea pharyngis) is situated behind the larynx at the level of the IV–VI cervical vertebrae. Superiorly on the anterior wall of the laryngeal pharynx is the opening leading into the larynx. This opening is bounded above by the epiglottis, laterally by the aryepiglottic folds, and below by the arytenoid cartilages of the larynx. On the lateral wall of the laryngeal pharynx lie fairly deep piriform recesses (recessus piriformes), where food particles and small foreign bodies can become lodged, particularly in children.

Of the seven openings of the pharynx (two openings of the auditory tubes, two choanae, and one opening each for the fauces, the larynx, and the esophagus), six close during swallowing. The choanae leading into the nasal cavity and the openings of the auditory tubes are closed because the soft palate is elevated by the contraction of its striated muscles. The fauces are closed by the dorsum of the Tongue, and the entrance to the larynx is closed by the epiglottis, which is pushed downward and backward by the pressure of the tongue's dorsum. The only opening that remains open during swallowing is the one leading from the pharynx into the esophagus.

The wall of the pharynx consists of a mucous membrane facing the pharyngeal cavity, a fibrous layer, a muscular coat, and an adventitial layer.

The mucous membrane of the pharynx is a direct continuation of the oral mucosa. At the level of the nasopharynx, it is lined with pseudostratified ciliated columnar epithelium, whereas in other parts it is lined with stratified squamous epithelium. Mucous glands are located within the pharyngeal mucosa, and their secretion, released into the pharynx, facilitates the gliding of food during swallowing.

The fibrous coat represents a modified submucosa of the pharynx and is characterized by high density, particularly in its upper section. By means of this coat, the pharynx is anchored to the external base of the skull. In the inferior (laryngeal) section, The Structure of this coat resembles a loose submucosal layer.

The most complex in Structure and function is the muscular coat, which is formed by Striated Muscle tissue. The inner circular layer of the muscular coat forms three pharyngeal constrictors, while the outer longitudinal layer forms two pharyngeal elevators.

The pharyngeal constrictors are much better developed than the Muscles of the longitudinal group. The fibers of the constrictors run anteroposteriorly, arch around the sides of the pharynx, and interlace with the fibers of the opposite side, forming the pharyngeal raphe (raphe pharyngis) along the midline of the posterior wall. A structural feature of the pharyngeal constrictors is their funnel-like shape, with each superior funnel fitting inside the one below it, which facilitates the propulsion of food.

The pharyngeal constrictors include the superior, middle, and inferior pharyngeal constrictors.

The superior pharyngeal constrictor (m. constrictor pharyngis superior) originates from the medial plate of the pterygoid process of the Sphenoid bone, the pterygomandibular raphe (a fibrous band stretched between the pterygoid hamulus and the Mandible), the mandible, and the ROOT of the tongue. The fibers of the superior constrictor pass backward and downward, coalescing in the midline on the posterior surface of the pharynx with the corresponding fibers of the opposite side.

The middle pharyngeal constrictor (m. constrictor pharyngis medius) arises from the greater and lesser horns of the Hyoid bone. From there, the fibers diverge in a fan-like manner upward and downward, heading toward the posterior surface of the pharynx, where they interlace with the muscle fibers of the opposite side. The upper edge of the middle pharyngeal constrictor overlaps the lower portion of the muscle fibers of the superior pharyngeal constrictor.

The inferior pharyngeal constrictor (m. constrictor pharyngis inferior) originates from the lateral surface of the thyroid and cricoid cartilages of the larynx. Its muscle fibers fan out posteriorly, inferiorly, horizontally, and superiorly, overlapping the lower half of the middle constrictor and fusing with the fibers of the corresponding muscle of the opposite side on the posterior surface of the pharynx.

The function of the pharyngeal constrictors is to successively narrow the pharyngeal cavity from top to bottom, thereby propelling food into the esophagus.

The muscles that elevate the pharynx include the stylopharyngeus and palatopharyngeus muscles.

The stylopharyngeus muscle (m. stylopharyngeus) is a thin, slender muscle. It originates from the styloid process of the Temporal bone, runs downward and forward, penetrates between the superior and middle constrictors, and terminates in the pharyngeal wall. Some of its bundles reach the upper border of the thyroid Cartilage. Function: elevates the Pharynx and Larynx.

The palatopharyngeus muscle (m. palatopharyngeus) was described previously along with the muscles of the soft palate (see "Oral Cavity").

The adventitial (connective tissue) coat of the pharynx is a continuation of the buccopharyngeal fascia, which covers the buccinator muscle and transitions into the adventitia of the esophagus.

Blood supply to the pharynx is provided by Branches of the ascending pharyngeal artery, the ascending and descending palatine Arteries, and branches of the facial artery, all originating from the External Carotid Artery. Venous blood drains via the pharyngeal plexus through pharyngeal Veins into the Internal jugular vein system. Lymphatic drainage goes to the retropharyngeal and deep cervical lymph nodes.

The pharynx is innervated by the pharyngeal nerve plexus, located beneath the middle pharyngeal constrictor and formed by branches of the vagus and glossopharyngeal nerves, as well as the cervical ganglion of the Sympathetic trunk.

The pharynx develops in early Embryogenesis from the region of the foregut corresponding to the third, fourth, and partially the fifth pharyngeal arches.

The pharynx of a newborn is funnel-shaped, featuring a tall, wide upper portion and a short, narrowed lower portion. The length of the newborn's pharynx is approximately 3 cm, its transverse dimension ranges from 2.1 to 2.5 cm, and its anteroposterior dimension is 1.8 cm. In newborns, the pharyngeal opening of the auditory tube is located at the level of the hard palate, lies close to the palatine velum, appears as a gaping slit-like opening. After 2–4 years, this opening shifts upward and backward, acquiring a rounded shape by the age of 12–14 years.

The tonsils develop most intensively During the first 2 years of life, after which their growth slows down. Following the age of 12–14 years, the pharyngeal tonsil grows very slowly, and later its growth ceases entirely, entering a period of partial involution. In adults, it is barely noticeable or entirely absent.