The pharynx (fayr’-inks) is the passageway that connects the nasal and oral cavities with the larynx and esophagus. It is part of both the respiratory and the digestive systems. Its digestive function is the transport of food from the mouth to the esophagus during swallowing.
The swallowing reflex is activated when food is pushed into the pharynx by the tongue. The soft palate moves superiorly, preventing food from entering the nasal cavity, and directs food inferiorly into the pharynx. At the same time, muscle contractions elevate the larynx, which causes the epiglottis to fold over and cover the opening into the larynx. This action prevents food from entering the larynx and directs it into the esophagus.
The esophagus (e-sof ‘-ah-gus) is a muscular tube that extends from the pharynx inferiorly through the mediastinum and the diaphragm to join with the stomach. When food is swallowed and enters the esophagus, peristaltic contractions propel the food toward the stomach. The esophageal mucosa produces mucus to lubricate the esophagus and aid the passage of food.
At the junction of the esophagus and stomach, the lower esophageal, or cardiac, sphincter (sfink’-ter) prevents regurgitation of stomach contents into the esophagus. But when the peristaltic wave that is propelling food toward the stomach reaches the sphincter, it relaxes and allows food to enter the stomach. The lower esophageal sphincter (LES) is a physiological sphincter rather than an anatomical one because it is not seen in cadavers. It is believed to be caused by muscle tone within the esophagus or surrounding diaphragm.
Failure of the LES to close properly allows for gastric secretions to regurgitate into the inferior esophagus. The gastroesophageal reflux (GER) irritates the esophageal lining and usually produces a burning sensation called “heartburn.” Causes of GER include malfunction of the LES, alcohol consumption, smoking, and excess acid production in the stomach. Avoiding foods that stimulate acid production in the stomach, such as caffeine and tomatoes, can reduce GER symptoms. Medications that neutralize stomach acid or reduce its production can also alleviate GER symptoms. GER that occurs chronically may indicate a more serious condition called Gastroesophageal Reflux Disease (GERD). The chronic esophageal irritation associated with GERD can lead to cellular changes that increase a person’s risk of esophageal cancer or Barrett esophagus, which involves changes in the esophageal lining to resemble that of the intestine.