What primarily triggers peristaltic waves in the esophagus?

• A. The food bolus moving through
• B. The stomach distension
• C. Chewing action only
• D. Spontaneous neural activity

Answer: (A)

The action of a food bolus in the esophagus is what starts the peristaltic wave. When the swallowed bolus distends the esophageal walls, stretch receptors detect that stretch and trigger a coordinated reflex that propagates a wave of smooth muscle contraction downward, pushing the bolus toward the stomach. This reflex is orchestrated by the enteric nervous system with input from the brainstem via the swallowing center. Chewing helps form the bolus, and stomach distension can affect motility downstream, but they are not the primary initiators of esophageal peristalsis. Spontaneous neural activity can occur, but the normal trigger for peristaltic waves during swallowing is the bolus entering and distending the esophagus.