Swallowing 101

Swallowing is a process that can be divided into several stages. The cephalic stage occurs when one is thinking about having a meal, and it induces the activity of swallowing. The oral stage, which is voluntary, is subdivided into three phases: chewing, salivation, and movement of the bolus. Mastication, or chewing, is the process by which food is crushed and ground by teeth. It increases the surface area of foods to allow more efficient breakdown by enzymes. The pharyngeal stage is involuntary and constitutes the passage of food through the pharynx into the esophagus. Finally, the esophageal stage is an involuntary phase that transports food from the pharynx to the stomach.

During the pharyngeal stage, the bolus of food enters the posterior mouth and pharynx, where it stimulates the epithelial swallowing receptor areas. This leads to a series of automatic pharyngeal muscle contractions, which prevent the reflux of food into the nasal cavities and trachea. The vocal cords of the larynx are closed, and the larynx is pulled upward and anteriorly by the neck muscles. The epiglottis swings backward over the opening of the larynx, preventing food from ever getting as far as the vocal cords. Finally, the upward movement of the larynx pulls up and enlarges the opening to the esophagus.