Physiology

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The upper esophageal sphincter forms the entrance to the esophagus. As the narrowest part of the alimentary tract, it is the first and often the most difficult obstacle for the endoscopist to surmount (Fig. 2.7). It is a muscular sphincter formed predominantly by the cricopharyngeal fibers of the constrictor pharyngeus muscle. This region forms a high-pressure zone 24 cm long with a resting pressure of 40-120 mmHg, making it extremely difficult to intubate. This pressure falls when the patient swallows, allowing the endoscope to pass through. The sphincter almost never has a visible lumen, since the relaxation phase during swallowing lasts for only a fraction of a second (Table 2.1).

Endoscopically, the upper esophageal sphincter appears as a lip-shaped eminence surrounding a transversely oriented, slitlike lumen (Figs. 2.7, 2.9). The stratified squamous epithelium of the esophagus itself normally appears reddish-gray with a smooth, glistening surface. It is not very transparent, but longitudinal, superficially branched venous plexuses can be seen beneath the mucosa.

Table 2.1 Upper esophageal sphincter

► Approximately 14 cm from the incisor teeth

► Slitlike lumen

► Difficult to see into the lumen

► Endoscope can be passed only during swallowing

► Caution: Avoid slipping into the piriform recess.

Fig. 2.7 Upper esophageal sphincter. The tip of the endoscope is positioned directly above the upper esophageal sphincter a The patient is breathing, and the esophageal sphincter is closed b The patient swallows, and the esophageal sphincter briefly opens

Fig. 2.7 Upper esophageal sphincter. The tip of the endoscope is positioned directly above the upper esophageal sphincter a The patient is breathing, and the esophageal sphincter is closed b The patient swallows, and the esophageal sphincter briefly opens

Upper esophageal sphincter

Fig. 2.8 Midsagittal scan through the head and neck (from: Möller and Reif, Normal Findings in CT and MRI. Stuttgart: Thieme 1999)

t = trachea ues = upper esophageal sphincter pr = piriform recess ce = cervical esophagus sc = spinal column

Upper esophageal sphincter

Fig. 2.8 Midsagittal scan through the head and neck (from: Möller and Reif, Normal Findings in CT and MRI. Stuttgart: Thieme 1999)

Fig. 2.9 Cross section just above the upper esophageal sphincter. During esophageal intubation, the upper esophageal sphincter is usually closed. It opens during swallowing, momentarily ex posing the lumen. At that time the endoscope can be advanced t = trachea ues = upper esophageal sphincter pr = piriform recess ce = cervical esophagus sc = spinal column

Fig. 2.9 Cross section just above the upper esophageal sphincter. During esophageal intubation, the upper esophageal sphincter is usually closed. It opens during swallowing, momentarily ex posing the lumen. At that time the endoscope can be advanced

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