Esophagus

the part of the alimentary canal of animals and man through which food passes. In invertebrates, the esophagus begins at the mouth opening or pharynx, extending in some animals to the beginning of the midgut or glandular stomach and in others to the masticatory stomach. In some flatworms and annelids, the esophagus is a tube connecting the pharynx to the midgut. Among mollusks, the esophagus is well developed only in gastropods and cephalopods, forming in many of these mollusks an ingluvies (crop). In arachnids and insects, the esophagus begins at the pharynx, and in crustaceans and myriapods, at the mouth opening. In higher crustaceans, king crabs, and most insects, the posterior section becomes the masticatory stomach, in which food is ground up. In echinoderms, the esophagus connects the mouth opening to the midgut; in most vertebrates, it connects the pharynx to the stomach. The length of the esophagus varies with the length of the cervical and thoracic parts of the trunk. In birds the esophagus is very long and forms the crop.

In man, the esophagus is a muscular tube about 25 cm long. It enters the abdominal cavity through the esophageal opening of the diaphragm and reaches the cardia. The esophagus narrows in three places: where it leaves the pharynx, where the trachea becomes divided into bronchi, and where the esophagus passes through the diaphragm. The walls of the esophagus consist of a layer of areolar tissue, an underlying muscular layer of external longitudinal and internal circular fibers, and a submucous layer and mucous membrane; the glands are situated in the submucous layer and the mucous membrane. The esophagus is innervated by the sympathetic, vagus, and cerebrospinal nerves. It is supplied with blood through the arterial branches of the inferior thyroid and subclavian arteries, thoracic aorta, and left gastric artery. The muscles of the esophagus contract reflexly during every swallowing movement. The contractions are in the form of waves originating in the upper part of the esophagus and extending along the entire length. The muscles arranged in rings contract successively, causing the bolus to move downward. Solid food passes through the esophagus in eight to nine sec on the average, and liquid food in one to two sec.

Diseases of the esophagus, which may be congenital or acquired, include such anomalies as atresia, congenital stenosis, and cysts; esophageal atony and paralysis; achalasia; diverticulum; hernia of the esophageal opening of the diaphragm; and esophagitis (inflammatory lesions), which may be acute, subacute, or chronic. Peptic esophagitis (reflux esophagitis) is caused by the repeated effects of active gastric juice, bile, or intestinal or pancreatic juice on the esophageal mucosa. Other esophageal irregularities include tuberculosis, syphilis, mycotic lesions, allergic and drug-induced lesions, and the presence of foreign bodies, in addition to injuries, burns, stenosis, benign and malignant tumors, and varicosity. Among the methods used to diagnose esophageal diseases are auscultation, roentgenologic and radio-isotopic examinations, esophagoscopy, biopsy and cytologic examination, and blind bougienage. Treatment, whether dietetic, medicamentous, or surgical, depends on the nature of the disease.