Swallowing is a very complex act, requiring the normal function of the brain, several nerves and muscles, two muscular valves, and an open, unconstricted esophagus, or swallowing tube.
The swallowing tract extends from the mouth to the stomach. The act of swallowing normally occurs in three phases. In the first phase, food or liquid is contained in the mouth by the tongue and palate (oral cavity). This phase is the only one we can control.
The second phase of swallowing begins when the brain makes the decision to swallow. At this point, a complex series of reflexes begin. The food is thrust from the oral cavity into the throat (pharynx). At the same time, two other events occur: A muscular valve at the bottom of the pharynx opens, allowing food to enter the esophagus, and other muscles close the airway (trachea) to prevent food from entering the airways. This second phase of swallowing takes less than half a second.
The third phase of swallowing begins when food enters the esophagus. The esophagus, which is about nine inches long, is a muscular tube that produces waves of coordinated contractions (peristalsis). As the esophagus contracts, a muscular valve at the end of the esophagus opens and food is propelled into the stomach. The third phase of swallowing takes six to eight seconds to complete.
A wide range of diseases can cause swallowing problems, including:
Disturbances of the brain such as those caused by Parkinson's disease, multiple sclerosis, or ALS (amyotrophic lateral sclerosis, or Lou Gehrig's disease)
Oral or pharynx muscle dysfunction such as from a stroke
Loss of sphincter muscle relaxation (termed "achalasia")
Esophageal narrowing such as from acid reflux or tumors