The esophagus is a muscular tube measuring about 25 cm (40 cm from the incisor teeth) extending from the pharynx at the cricoid cartilage to the cardia of the stomach. It pierces the left crus of the diaphragm and has an intraabdominal portion of about 1.5 cm in length.
The esophageal mucosa consists of a nonkeratinizing squamous epithelium, lamina propria extending into the basal layer as rete pegs, and muscularis mucosa, which is sparse and thin in the upper portion but thicker near the gastroesophageal junction.
The submucosa contains mucous glands and an extensive lymphatic plexus in a connective tissue network.
Between the submucosa and muscularis propria are the cell bodies of secondary neurons forming the Auerbach’s plexus.
The muscularis propria, the main muscle layers of the esophagus, is composed of inner circular and outer longitudinal coats. In the upper part, these are striated. There is a gradual change to smooth muscle in the middle. In the lower third of the esophagus, both of these coats are entirely composed of smooth muscle.
Between the muscle layers, the myenteric plexus contains the cell bodies of other secondary neurons.
The esophagus does not have a serosal layer.
Lower esophageal sphincter. The distal 3 to 4 cm of the esophagus constitutes a zone of increased resting pressure in an asymmetric fashion. This area, called the lower esophageal sphincter (lower esophageal sphincter), behaves both physiologically and pharmacologically as a distinct entity from the esophageal smooth muscle immediately adjacent to it. Basal lower esophageal sphincter pressure is normally 10 to 25 mm Hg higher than intragastric pressure and drops promptly (within 1-2 seconds) with swallowing. The lower esophageal sphincter control remains poorly understood but is thought to involve the complex interaction of neural, hormonal, and myogenic activities.
Physiology of esophageal function
The function of the esophagus is to transport food and secretions from the mouth to the stomach. This coordinated process operates regardless of the force of gravity.
A swallow begins when a liquid or solid bolus is propelled to the back of the mouth into the pharynx by the tongue. The upper esophageal sphincter, the cricopharyngeus, which is just below the pharynx, relaxes, allowing the bolus to pass into the upper esophagus. In response to swallowing, an orderly, progressive contraction of the esophageal body occurs (primary peristalsis), propelling the bolus down the esophagus. When the esophagus is distended by a bolus (i.e., with regurgitation), secondary peristaltic contractions are initiated. The lower esophageal sphincter relaxes as the bolus reaches the lower esophagus, allowing passage of the food into the stomach.
The relaxation of the upper esophageal sphincter and peristalsis in the upper esophagus are initiated by the voluntary act of swallowing, controlled by the swallowing center in the brainstem and the fifth, seventh, ninth, tenth, eleventh, and twelfth cranial nerves. These nerves coordinate the movement of the bolus to the hypopharynx, closure of the epiglottis, relaxation of the upper esophageal sphincter, and contraction of the striated muscle of the upper esophagus. The sequential nature of this function is due to progressive activation of nerve fibers carried in the vagus nerve controlled through a central mechanism.
The peristalsis in the smooth-muscle portion of the esophagus is regulated by activation of neurons located in the myenteric plexus with cholinergic neural transmission. The vagi innervate the upper esophagus in its striated muscle portion only. If the vagi are cut below the level of mid esophagus, peristalsis in the lower half of the esophagus and the function of the lower esophageal sphincter remain intact.
Diagnostic approach of Dysphagia
The treatment of oropharyngeal dysphagia depends on the specific cause.
Neurologically impaired patients require special attention during feedings with respect to dietary texture; body, head, and neck position; size and frequency of food bolus administration, and aspiration precautions. Patients should sit fully upright in bed or in a chair while eating. The bolus size should be small in sips or bites. Foods with thicker textures (e.g., thick liquids and pudding textures) are often better tolerated than clear liquids. Spicy, acidic foods and coffee, tea, and alcohol should be avoided. After meals, patients should remain in the upright position for an additional 1 to 3 hours to minimize the risk of aspiration. The head of the bed should be elevated during resting and sleeping hours.
Systemic disease. If the disorder is secondary to a systemic disease, the treatment needs to be directed to the primary disease. Rings, webs, and strictures. Of the structural disorders, the treatment of rings and webs is the most gratifying to both the patient and the physician. Dilatation with a mercury-filled bougie usually relieves the symptoms. Esophageal strictures may also be dilated under endoscopic guidance with balloon dilators or savory dilators that allow progressively larger dilators passed to be over a guidewire. Motility disorders. Treatment of motility disorders is difficult, and variable results are obtained.