Читать книгу The Esophagus - Группа авторов - Страница 153

Swallowing is arbitrarily divided into four phases: (i) ingestion and bolus preparation, (ii) the oral phase, (iii) the pharyngeal phase, and (iv) the esophageal phase. In reality, swallowing is a programmed sequence of skeletal and then smooth muscle contraction, altered by sensory input [13]. There are no distinct phases of swallowing.

Figure 6.4 Relationship of larynx to pharynx in a patient who has aspirated. (A) Frontal view of the pharynx during inspiration. The larynx is related to the lower hypopharynx, causing an extrinsic mass impression on the pharynx anteriorly. The true and false vocal cords are widely separated (the right true [t] and right false [f] vocal cords are identified). The laryngeal ventricle (arrow) is identified. The muscular processes of the arytenoids (arrowheads) are separated. (B) Frontal view of the pharynx during a modified Valsalva maneuver demonstrates that the true vocal cords (right cord – t) are now apposed. The muscular processes of the arytenoids (arrowheads) are close together. The space between them is the interarytenoid notch (small arrow). The pharynx is markedly distended in its posterior portion (large arrow), ballooning posterior to the confines of the thyroid cartilage (arrow – T). The pharynx also bulges at the thyrohyoid membrane (open arrow).

Source: Reproduced from Rubesin and Glick [23], with permission.

A bolus is selected and brought to the lips by volitional activity. A liquid is sucked or poured into the mouth. A solid is placed on top of the tongue. Liquids do not require much oral manipulation and are therefore easily transferred to the oropharynx. Solids must be chewed and mixed with saliva to achieve a satisfactory consistency for swallowing. During bolus preparation, the bolus is contained in the oral cavity in young adults. Older “normal” adults frequently spill the bolus prematurely into the oropharynx before swallowing [12].

Once the bolus is prepared, the tongue collects and sizes the bolus and transfers it into the oropharynx. The tongue tip rises to appose the hard palate, and the mid tongue forms an inclined plane directing the bolus into the oropharynx [10] (Figure 6.6). The velopharyngeal portal is closed as the soft palate rises to appose the posterior pharyngeal wall and the superior constrictor muscle contracts to appose the soft palate [9].

The pharynx and larynx are elevated by the suprahyoid muscles and intrinsic elevators of the pharynx. Pharyngeal‐laryngeal elevation participates in closure of the laryngeal aditus and laryngeal vestibule, epiglottic tilt, and opening of the pharyngoesophageal segment [8].

Epiglottic tilt is accomplished by contraction of the suprahyoid muscles, the thyrohyoid muscle, and the intrinsic epiglottic muscles. Elevation of the hyoid bone by the suprahyoid muscle group pulls on the hyoepiglottic ligament attached to the petiole (lower portion) of the epiglottic cartilage. Hyoid elevation pulls the petiole superiorly, tilting the upper epiglottis towards the horizontal in a fulcrum‐like motion. Contraction of the aryepiglottic and oblique arytenoid muscles and the thyroepiglottic muscles then inverts the epiglottis.

Figure 6.5 Postcricoid squamous mucosa. Just posterior to the cricoid cartilage, the anterior wall of the pharyngoesophageal segment has redundant mucosa that changes size and shape during swallowing. Note how the mucosa has a wavy appearance (arrows). When identified, this mucosa identifies the level of the cricoid cartilage and the level of the cricopharyngeus during pharyngography.

Source: Reproduced from Rubesin [6], with permission.

The epiglottis acts as a stream diverter, directing the bolus into the lateral swallowing channels. The tilting epiglottis also helps cover the laryngeal vestibule. The larynx closes in a retrograde fashion. The true vocal cords close at the beginning of the swallow, followed by the false vocal cords and the remainder of the laryngeal vestibule. If a portion of the bolus has penetrated the laryngeal vestibule, it is pushed back into the hypopharynx by retrograde laryngeal closure. The bolus flows through the pharynx by a combination of gravity, elevation of the pharynx over the bolus, tongue push, and sequential contraction of the constrictor muscles. Although the upper esophageal sphincter relaxes at the beginning of a swallow, the pharyngoesophageal segment does not open until the bolus reaches the lower hypopharynx. Elevation of the larynx and pharynx pulls the anterior wall of the pharyngoesophageal segment anteriorly. Tongue base retraction, constrictor contraction, and gravity increase bolus pressure to open the pharyngoesophageal segment.