Disorders of Swallowing and of the Esophagus
Paralysis of the Swallowing Mechanism. Damage to the 5th, 9th, or 10th cerebral nervecan cause paralysis of significant portions of the swallowing mechanism. Also, a few diseases, such as poliomyelitis or encephalitis, can prevent normal swallowing by damaging the swallowing center in the brain stem. Finally, paralysis of the swal-lowing muscles, as occurs in muscle dystrophy or in failure of neuromuscular trans-mission in myasthenia gravis or botulism, can also prevent normal swallowing.
When the swallowing mechanism is partially or totally paralyzed, the abnormal-ities that can occur include (1) complete abrogation of the swallowing act so that swallowing cannot occur, (2) failure of the glottis to close so that food passes into the lungs instead of the esophagus, and (3) failure of the soft palate and uvula to close the posterior nares so that food refluxes into the nose during swallowing.
One of the most serious instances of paralysis of the swallowing mechanism occurs when patients are under deep anesthesia. Often, while on the operating table, they vomit large quantities of materials from the stomach into the pharynx; then, instead of swallowing the materials again, they simply suck them into the trachea because the anesthetic has blocked the reflex mechanism of swallowing. As a result, such patients occasionally choke to death on their own vomitus.
Achalasia and Megaesophagus. Achalasiais a condition in which the lower esophagealsphincter fails to relax during swallowing. As a result, food swallowed into the esophagus then fails to pass from the esophagus into the stomach. Pathological studies have shown damage in the neural network of the myenteric plexus in the lower two thirds of the esophagus. As a result, the musculature of the lower esoph-agus remains spastically contracted, and the myenteric plexus has lost its ability to transmit a signal to cause “receptive relaxation” of the gastroesophageal sphincter as food approaches this sphincter during swallowing.
When achalasia becomes severe, the esophagus often cannot empty the swallowed food into the stomach for many hours, instead of the few seconds that is the normal time. Over months and years, the esophagus becomes tremendously enlarged until it often can hold as much as 1 liter of food, which often becomes putridly infected during the long periods of esophageal stasis. The infection may also cause ulcera-tion of the esophageal mucosa, sometimes leading to severe substernal pain or even rupture and death. Considerable benefit can be achieved by stretching the lower end of the esophagus by means of a balloon inflated on the end of a swallowed esophageal tube. Antispasmotic drugs (drugs that relax smooth muscle) can also be helpful.
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