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DEVELOPMENT OF THE ESOPHAGUS

As early as the fourth week in development, the esophagus of the human embryo is merely a sphincter or constricted part of the primitive foregut, between the pharynx and stomach, as observed by Keith (1948) (Fig. 122-1). During the sixth and seventh weeks of gestation, the esophagus undergoes rapid elongation as cephalic development separates the head and neck from the thorax. The elongation is facilitated by development of the lungs and pleural cavities, which push the stomach dorsally and inferiorly (Fig. 122-2). Keith suggested that the esophagus is of dual origin, with an upper retrotracheal part originating from the pharyngeal portion and an infratracheal part originating from the pregastric segment of the foregut. During the sixth week of development, the esophagus is only 2 mm long, but at birth it extends to 100 mm. Its superior limit is marked by the inferior cricopharyngeal portion of the inferior pharyngeal constrictor. Fyke and Code (1955) recorded that the cricopharyngeal part of the inferior pharyngeal constrictor relaxes suddenly during swallowing and simultaneously lengthens the vocal folds of the larynx. The lower limit of the esophagus is marked by its entrance to the stomach, in a region that constitutes a barrier to reflux of gastric contents, but it is not marked by an anatomically recognizable sphincter. Basmajian (1980) indicated that at lower thoracic levels, the esophagus is supported away from the aorta, azygos vein, and body of the vertebra, which permits advancement of the esophagus away from the vertebral column. As the lungs approach each other in inspiration of an erect subject, a retroesophageal window is presented in radiographs.
Keibel and Mall (1912) reported that between 8.4 and 16 mm (fifth to seventh weeks), the esophagus is crescentic, with the concavity of the crescent directed toward the trachea (Fig. 122-2). Its upper part is round, but as it descends, it appears transversely elliptic. Near the level of tracheal bifurcation, it becomes round again, and finally it assumes an elliptic shape in the dorsoventral direction. The esophagus remains patent during this early period, save for a nonspecific reticular coagulum.
Editors: Shields, Thomas W.; LoCicero, Joseph; Ponn, Ronald B.; Rusch, Valerie W.
Title: General Thoracic Surgery, 6th Edition
Copyright ©2005 Lippincott Williams & Wilkins
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