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Swallowing
Objectives
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Describe the oral and pharyngeal events taking place during a swallow.
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Describe the pressures within the esophagus and oral stomach at rest and during a swallow.
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Explain the regulation involved during a swallow, including its initiation and peristalsis through the esophagus.
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Understand the process of receptive relaxation of the oral stomach, its function, and regulation.
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Understand gastric esophageal reflux disease (GERD) and its causes.
Swallowing consists of chewing, a pharyngeal phase, movement of material through the esophagus, and the relaxation of the stomach to receive the ingested material. Swallowing is almost purely a motility function. Digestion and absorption are minimal, in part because transport of the bolus into the stomach takes only seconds.
Chewing
Chewing has three major functions: (1) it facilitates swallowing by reducing the size of ingested particles and thus also prevents damage to the lining of the pharynx and esophagus; (2) it mixes food with saliva, which exposes the food to digestive enzymes and lubricates it; and (3) it increases the surface area of ingested material and thereby increases the rate at which it can be digested.
The act of chewing is both voluntary and involuntary, and most of the time it proceeds by reflexes void of conscious input. The chewing reflex is initiated by food in the mouth that inhibits muscles of mastication and causes the jaw to drop. A subsequent stretch reflex of the jaw muscles produces a contraction that automatically raises the jaw and closes the teeth on the bolus of food. Compression of the bolus on the mucosal surface of the mouth inhibits the jaw muscles to repeat the process.
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