The normal swallowing mechanism can be divided into four stages: preparatory, oral, pharyngeal and esophageal. The first two phases are under the control of the person swallowing (voluntary); the latter two phases are reflexively triggered once the food reaches the throat (involuntary).
Food is placed into the mouth. A food bolus is formed by chewing and moistened with saliva. The bolus is kept in the mouth and prepared for swallowing.
The food bolus is moved from the mouth to the back of the throat (Pharynx). The uvula and soft palate elevate to keep the food out of the nose and the back of the tongue pushes the food back into the pharynx.
The food bolus in the pharynx triggers the swallowing reflex. The bolus of food is squeezed into the esophagus from the pharynx. Breathing stops during this part of swallowing, with the voice box (larynx) closing in order to prevent food from entering the airway (aspiration).
At the junction of the throat (pharynx) and esophagus, there are bands of muscle fibers (cricopharyngeal muscle) that create a one way valve.The cricopharyngeal muscle relaxes to allow the food to pass and tightens to keep the esophageal contents from returning back into the throat. This one way valve made of the cricopharyngeal muscle is also known as the upper esophageal sphincter.
The food bolus moves through the esophagus into the stomach. At the junction of the esophagus and stomach, there are bands of muscle fibers that create a one way valve (upper esophageal sphincter).The muscles relaxes to allow the food to pass and tighten to keep the stomach contents from returning back into the esophagus.