Swallowing

Swallowing, a complex reflexive act having the purpose of conducting food from the oral cavity into the stomach while protecting the respiratory passages and nasal cavity from entry of food particles. It consists of voluntary and involuntary movements of the corresponding muscles, which have been studied precisely with the aid of X-rays by Cannon. The process of S. can be divided into three phases. After closing the mouth and compressing the jaws, the tip, back, and root of the tongue are sequentially pressed against the hard palate, as a result of which the food bolus is pushed toward the open pharynx. From the moment the food bolus passes behind the palatine arches, involuntary swallowing movements begin. At this moment, closure of the cavum pharyngo-nasale occurs by means of the following mechanism: a reflex from the soft palate (in the rabbit) or from the posterior wall of the pharynx (dog, cat) causes horizontal elevation and tension of the soft palate. The posterior and lateral walls of the pharynx are pressed by the superior constrictor muscle of the pharynx against the posterior edge of the soft palate, with the edges of the posterior palatine arches approaching each other. At the same time, closure of the larynx occurs as follows: the mm. genio-, stylo-, mylo-, thyreo-hyoidei and the anterior belly of digastricus contract and lift the hyoid bone and larynx upward and forward under the root of the tongue, which presses the epiglottis and closes the entrance to the larynx. At the same time, by approximation of the arytenoid cartilages and vocal cords, the glottis is closed. After this, by contraction of the middle and inferior constrictors of the pharynx, the food bolus is driven into the esophagus, where it is further propelled by peristaltic movements of the latter (in the upper part by means of striated, in the lower part of smooth musculature). The duration of the act of S. in humans averages 6-7 seconds and depends on the degree of density and volume of the food bolus. Coordination of all complex swallowing movements is carried out by means of the S. center, located at the bottom of the fourth ventricle, near ala cinerea (Marckwald). The role of centripetal nerves in the act of S. is played by the n. trigeminus, n. glosso-pharyngeus, n. laryngeus superior. Centrifugal impulses go along the n. hypoglossus and the motor branches of the plexus pharyngei. The motor nerve for the esophagus is the n. vagus. When both vagus nerves are severed, food stagnates in the lower part of the esophagus.

L. Stern. Disorders of swallowing. The most frequent cause of disorder of S. (dysphagia) are various pathological processes in the oral cavity, pharynx, and larynx. One can even say that rare diseases in this area are not accompanied by disturbance of the act of swallowing. The degree of these disorders varies. Severe difficulties in swallowing are caused either by mechanical obstacles arising during passage of food and liquid from the oral cavity through the pharynx into the opening of the esophagus, or by severe pain that increases during S. The etiology of disorders of S. varies. Narrowing of the lumen of the oral cavity and pharynx, caused by tumors of the floor of the mouth, tongue, and pharynx, significantly hinders swallowing, especially of solid food. Benign tumors in the pharynx (fibrous polyps, papillomas, angiomas) comparatively rarely cause difficulty in S. Only with their large volume does a disorder of S. appear. Disorders of S. in malignant tumors depend on the size and location of the tumor. Malignant neoplasms, which develop most frequently on the lateral wall of mesopharynx, on the tonsils or in their vicinity, at first do not cause noticeable disorders of S.; they appear only when the tumor reaches a significant volume. If the tumor is in epipharynx on its anterior wall, then significant difficulties in S. appear already in the early stage of its development. Ulcerated cancerous neoplasms of the palatine tonsils are accompanied by severe pain, with which S. is impossible. Lockjaw (trismus) due to interstitial myositis of the masticatory muscles is observed: 1) in periostitis and periodontitis of the molars, 2) in delayed eruption of wisdom teeth, 3) in peritonsillar abscess (suppurative angina), 4) in deep phlegmons (abscesses) of the root of the tongue, and 5) more rarely in peritonsillitis lingualis. Besides the mechanical difficulty caused by inability to open the mouth, the main role here is played by pain, which is especially severe in peritonsillar abscess. Unbearable pain in abscess of the root of the tongue makes swallowing even liquid food impossible. Severe disorders of swallowing are also caused by retropharyngeal abscesses, developing in the retropharyngeal space as a result of acute suppuration of retropharyngeal lymphatic glands. In deformity or even complete loss of the tongue, only chewing is disturbed, but swallowing occurs normally. Congenital or acquired (most often after gummatous syphilis) defects of the hard and soft palate cause disturbance of the normal act of S., with particles of food entering the nasal cavity or nasopharynx. Adhesion of the palatal curtain to the posterior wall of the pharynx leads to disturbance of mobility of the soft palate, as a result of which during the act of S. there is no complete separation of the oral cavity from the nasopharynx and particles of food can enter the nasopharynx. After extensive ulcers on the posterior wall of the pharynx, diaphragms (scar tissue) may form, located between the root of the tongue and the posterior wall of the pharynx. In severe cases, only a small opening remains, through which only liquid food can pass. Disorders of S. in inflammatory processes in the pharynx, e.g., in acute catarrhal, lacunar, and follicular anginas, in diphtheria and scarlatinal angina, depend less on mechanical obstacles caused by swelling of soft tissues than on pain, which increases during S. depending on the action of the pharyngeal muscles. The degree of disorder of S. by no means corresponds to the nature of ulcerative and infiltrative processes in the pharynx, nasopharynx, and larynx. Especially prominent are severe pains and associated disorders of S. in tuberculous ulcers in the pharynx and larynx, in localization of ulcers on the posterior wall of the larynx, on the epiglottis and aryepiglottic ligaments, as well as in perichondritis of the larynx, whereas ulcerative processes on the true and false vocal cords do not affect S. In the lupous form of tuberculosis, S. occurs without hindrance. Syphilitic manifestations as a rule do not cause noticeable disorders of swallowing. But if the gummatous process involves the entire palatal curtain and arches, then due to insufficient closure of epipharynx, disturbance of swallowing results. Since the mucous membrane in epipharynx is more sensitive than in the pharynx, gummas on the posterior and lateral walls of the nasopharynx are sometimes accompanied by severe pain during S. Choanal polyps and true nasopharyngeal fibroma cause disturbance of S. only if they hang down into the pharynx. Gummatous infiltrates and ulcers of the larynx are accompanied by insignificant disturbances of S. Severe disorders of S. and pain occur only in the presence of perichondritis of the larynx. Finally, foreign bodies in the pharynx or at the entrance to the esophagus can cause difficulty in S. Severe disorders of S. are caused by sharp foreign bodies, although of small size, due to the pains accompanying the act of SWALLOWING.

K. Orleans. Paralysis of swallowing is observed in lesions of the vagus nerve or its nuclei in the medulla oblongata or finally of its supranuclear conductors on both sides (pseudobulbar paralysis). In complete paralysis of S., it is completely impossible, feeding can be done only with the aid of a tube. In paresis, weakness of the pharyngeal muscles is observed, as a result of which food is not pushed energetically enough to the esophagus; due to insufficient tension of the soft palate, the oral cavity is not separated to the proper degree from the nasal cavity, and liquid food flows out through the nose; finally, at the moment of S., the epiglottis is not pressed against the entrance to the larynx, as a result of which food enters the respiratory passages, which presents a very great danger to the patient - immediate death from suffocation or death from subsequent aspiration pneumonia may occur. Unilateral paralysis of the vagus nerve usually gives insignificant disorders of S. Especially characteristic in this is the 'curtain-like' displacement of the wall of the pharynx to the healthy side. Spasms of swallowing are especially characteristic in tetanus and in rabies and are a result of increased reflex excitability of the muscles of the pharynx. Every attempt at S., especially of liquids, causes an explosion of agonizing spastic tonic contractions. Sometimes such spasms are caused by only the sight of water, sometimes even only by the thought of it (hydrophobia). In some cases of tetanus, this symptom is so prominent in the picture of the disease that one speaks of tetanus hydrophobicus.