Pharynx

The pharynx is a fibromuscular passageway that connects the nasal and oral cavities to the larynx and esophagus. It serves both the respiratory and digestive systems as a channel for air and food. The upper region, the nasopharynx, is posterior to the nasal cavity. It contains the pharyngeal tonsils, or adenoids, functions as a passageway for air, and has no function in the digestive system. The middle region posterior to the oral cavity is the oropharynx. This is the first region food enters when it is swallowed. The opening from the oral cavity into the oropharynx is called the fauces. Masses of lymphoid tissue, the palatine tonsils, are near the fauces. The lower region, posterior to the larynx, is the laryngopharynx, or hypopharynx. The laryngopharynx opens into both the esophagus and the larynx.

Food is forced into the pharynx by the tongue. When food reaches the opening, sensory receptors around the fauces respond and initiate an involuntary swallowing reflex. This reflex action has several parts. The uvula is elevated to prevent food from entering the nasopharynx. The epiglottis drops downward to prevent food from entering the larynx and trachea in order to direct the food into the esophagus. Peristaltic movements propel the food from the pharynx into the esophagus.

Esophagus

The esophagus is a collapsible muscular tube that serves as a passageway between the pharynx and stomach. As it descends, it is posterior to the trachea and anterior to the vertebral column. It passes through an opening in the diaphragm, called the esophageal hiatus, and then empties into the stomach. The mucosa has glands that secrete mucus to keep the lining moist and well lubricated to ease the passage of food. Upper and lower esophageal sphincters control the movement of food into and out of the esophagus. The lower esophageal sphincter is sometimes called the cardiac sphincter and resides at the esophagogastric junction.