A problem involving any of the phases of swallowing can result in Dysphagia. Swallowing is the interplay between two separate but related functions, airway protection and bolus transport. Airway protection is the ability to prevent food from entering the trachea (aspiration) while eating.
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).