The throat (pharynx—see also Throat) lies behind and below the mouth. When food and fluids leave the mouth, they pass through the throat. Swallowing of food and fluids begins voluntarily and continues automatically. A small muscular flap (epiglottis) closes to prevent food and fluids from going down the windpipe (trachea) toward the lungs. The back portion of the roof of the mouth (soft palate) lifts to prevent food and fluids from going up the nose. The uvula, a small flap attached to the soft palate, helps prevent fluids from passing upward into the nasal cavity.
(See also Overview of the Digestive System.)
The esophagus is a thin-walled, muscular channel lined with mucous membranes that connects the throat with the stomach. Food and fluids are propelled through the esophagus not only by gravity but also by waves of rhythmic muscular contractions called peristalsis. At either end of the esophagus are ring-shaped muscles (the upper and lower esophageal sphincters), which open and close. The esophageal sphincters normally prevent the contents of the stomach from flowing back into the esophagus or throat.