Anatomy & Physiology

Anatomy & Physiology Study Guide circular muscle layer of the esophagus typically prevents air from entering the esophagus if it is relaxed. A comparable zone at the inferior end of the esophagus usually remains in a state of active contraction. This condition prevents the backflow of materials from the stomach into the esophagus. Swallowing Swallowing, or deglutition, is a complex process that can be initiated voluntarily but proceeds automatically once it begins. Although you take conscious control over swallowing when you eat or drink, swallowing is also controlled at the subconscious level. For example, swallowing occurs at regular intervals as saliva collects at the back of the mouth. Each day you swallow approximately 2400 times. Swallowing can be divided into buccal, pharyngeal, and esophageal phases: •

The buccal phase begins with the compression of the bolus against the hard palate. Subsequent retraction of the tongue then forces the bolus into the oropharynx and assists in the elevation of the soft palate, thereby sealing off the nasopharynx. The buccal phase is strictly voluntary.

Achieve Page 319 The pharyngeal phase begins as the bolus comes into contact with the palatoglossal and palatopharyngeal arches and the posterior pharyngeal wall. The swallowing reflex starts when the passage of the bolus is stimulated by tactile receptors on the palatal arches and uvula. Then the information is relayed to the swallowing center of the medulla oblongata over the trigeminal and glossopharyngeal nerves. It takes less than a second for the pharyngeal muscles to propel the of 368

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