What is the physical change in food when it enters esophagus?

Peristalsis: As food enters the esophagus, it undergoes a series of involuntary muscle contractions known as peristalsis. These waves of muscular contractions propel the food bolus downward toward the stomach without any chewing or further physical breakdown occurring within the esophagus.

Peristalsis involves the coordinated movement of smooth muscles arranged in circular and longitudinal layers within the esophageal walls. The circular muscles contract behind the food bolus, creating a high-pressure zone that pushes the food forward. Simultaneously, the longitudinal muscles relax to create a low-pressure zone ahead of the food, allowing it to move with ease.

No Chemical or Mechanical Breakdown: Unlike the oral cavity, which is involved in the physical breakdown of food through chewing, and the stomach, which initiates chemical digestion, the esophagus serves primarily as a muscular passageway. There are no digestive enzymes or other chemicals produced in the esophagus to alter the food composition. Therefore, food does not undergo any significant chemical or mechanical changes as it transits through the esophagus.

Once the food bolus reaches the lower esophageal sphincter (LES), a ring-like muscle at the junction of the esophagus and stomach, it relaxes to allow the food to pass into the stomach. The LES then contracts again to prevent the backward flow of gastric contents into the esophagus, maintaining the one-way movement of food through the digestive tract.