What marks the beginning of the esophageal phase of swallowing?

• A. The bolus enters the stomach
• B. The bolus passes through the upper esophageal sphincter
• C. The bolus enters the pharynx
• D. The bolus begins swallowing in the oral cavity

Answer: (B)

The key idea here is understanding how swallowing is divided into phases and what marks the shift to the next one. The esophageal phase starts when the bolus passes through the upper esophageal sphincter into the esophagus. That relaxation and opening of the sphincter signals that the food is no longer in the pharynx and is now being transported down the esophagus by peristaltic waves toward the stomach.

Before this moment, the bolus is moved to the esophagus during the oral and pharyngeal phases. Entering the stomach happens after the esophagus has moved the bolus down, not at the start. Entering the pharynx occurs during the pharyngeal phase, and the bolus beginning in the oral cavity initiates the oral phase.