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- Describe the functional anatomy of the esophagus and related structures, and their innervation
- Understand the roles played by the oral cavity, pharyngeal structures, and esophagus in transferring food from the mouth to the stomach during swallowing
- Discuss how the contents of the respiratory and digestive systems are kept separate
- Define the mechanisms and functions of primary and secondary esophageal peristalsis
- Describe the roles played by the upper and lower esophageal sphincters in esophageal motility
- Understand how the relaxation of these structures is coordinated with the swallow
- Describe how the lower esophageal sphincter protects against reflux of gastric contents
- Understand how belching occurs
- Discuss disease states in which esophageal motility and/or swallowing are abnormal
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Role and Significance
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The esophagus is a muscular tube that serves to transfer food from the mouth to the stomach. Under normal circumstances, food resides in the esophagus for only a few seconds and thus there is no time for it to be acted upon by any esophageal secretions. Thus, an understanding of the physiology of the esophagus relates primarily to its motility functions. In addition to moving the food along its length in the process of swallowing, the movements of the esophagus and related oral and pharyngeal structures must be carefully regulated to avoid misdirection of the food into the respiratory tract, or respired air into the digestive system. At rest, the esophagus is a relaxed structure that is closed off at both ends by sphincters—the upper and lower esophageal sphincters, respectively. These sphincters not only cooperate in the act of swallowing, or
deglutition, but also prevent backflow of gastric contents into the esophageal lumen or oral cavity. However, under specific circumstances, the esophagus does allow for retrograde movement. This occurs normally for air swallowed with the meal, in the process of belching, or abnormally during vomiting. During retrograde movement in humans and most mammals, the esophagus itself is a passive conduit; that is, there are no specific motility functions that propel vomitus or air along the length of the tube. Note that the process of vomiting will be discussed in detail in
Chapter 8.
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The process of swallowing, as well as other esophageal motility functions, is under close regulatory control. Swallowing can be initiated voluntarily, but thereafter reflects an automatic reflex that involves, sequentially, impulses from the brainstem, processing of this information through vagal centers in the central nervous system, direct effects of parasympathetic vagal efferents on esophageal muscle layers, and relay of information via the enteric nervous system (
Figure 7–1). Movement of materials along the length of the esophagus is aided by gravity, but predominantly depends on a coordinated series of muscle contractions and relaxations that make up the propulsive motility pattern known as
peristalsis.
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