The esophageal sphincters are bands of muscles at the top and bottom of the esophagus — the muscular tube that passes food and drink from the mouth to the stomach. Esophageal sphincters open and close the esophagus at either end.

The top sphincter prevents air from flowing into the esophagus while breathing, while the bottom sphincter prevents food from flowing back up the esophagus. Doctors call these sphincters the upper esophageal sphincter (UES) and the lower esophageal sphincter (LES).

Disorders of the esophageal sphincters may affect breathing, eating, and digestion.

For example, weakness in or pressure on the lower esophageal sphincter may cause food to flow back up the esophagus, causing reflux and the sensation of heartburn.

Conversely, when the LES does not relax to allow food to pass through, food may remain in the esophagus.

Dysfunction of the UES can make swallowing food difficult or painful. This phenomenon, called dysphagia, can happen when a person has physical or neurological injuries. In older adults, dementia is a common cause.

This article examines how the esophageal sphincter works, conditions that can cause its dysfunction, and treatment options for these conditions.

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The lower esophageal sphincter includes a group of smooth muscles at the base of the esophagus.

These muscles open to allow food to flow into the stomach. They also help the esophagus initiate contractions that move food downward and prevent it from flowing back up.

The upper esophageal sphincter, which doctors may also call the pharyngoesophageal sphincter, is a round group of striated muscles that opens and closes the esophagus. It is usually closed when a person is not eating.

It prevents air from entering the esophagus, such as when a person is talking. It also prevents contents of the esophagus from flowing back up into the throat.

The esophagus creates rhythmic contractions from the UES to the LES to move food downward and out of the esophagus. Doctors call these contractions peristalsis.

The main role of the esophagus is to help move food from the throat to the stomach. While gravity encourages food to move downward, the sphincters also play a role by closing off the top of the esophagus and opening the bottom to allow food to pass into the stomach.

The esophageal sphincters can also help the body dispose of harmful substances. For example, when a person vomits, the UES must open up to eliminate food from the esophagus.

With normal swallowing, the UES opens only when a person is swallowing food and otherwise remains closed. Peristaltic contractions then move the food down the esophagus. At the bottom of the esophagus, the LES opens to allow food to empty into the stomach.

Problems with the UES can cause:

  • difficulty swallowing
  • coughing and gagging
  • the sensation that something is in the throat
  • malnourishment

Problems with the LES can cause:

  • food to be trapped in the esophagus
  • reflux and acid reflux
  • malnourishment
  • injuries to the esophagus
  • an increased risk of esophageal cancer
  • aspiration – a buildup of esophageal contents in the lower esophagus increases the risk of food and liquid penetrating the airway, which can cause recurrent

Food most typically becomes trapped in three areas of the esophagus:

  • at the cricopharyngeus muscle near the UES
  • as it travels downward next to the aortic arch in the chest
  • near the diaphragm

People with esophageal sphincter dysfunction are especially vulnerable to trapped food in these areas.

Some common conditions affecting the esophageal sphincters include:

  • Achalasia: This is where the LES does not relax to allow the esophagus to move food downward and toward the stomach. This can cause food to remain in the esophagus.
  • Reflux: Reflux happens when food moves back up the esophagus and sometimes into the throat. This may occur when the lower esophageal sphincter does not close or when pressure from surrounding structures forces it open.
  • Esophageal injury: Injuries to the esophagus, such as tears and esophagitis, which is inflammation of the esophagus, can happen when acidic contents of the stomach travel back up the esophagus. Dysfunction of the LES can increase the risk of this happening.
  • Dysphagia: Dysphagia is swallowing dysfunction that causes a person to perceive swallowing pain or difficulty or to have actual physical impediments to swallowing. A person might cough or gag.

The right treatment depends on the reason for the symptoms. For example, people with neurological issues, such as dementia, or who have had a stroke often have dysphagia from upper esophageal dysfunction.

Weakness in the esophagus due to age or injuries may also play a role in esophageal disorders.

Some treatment options include:

  • lifestyle changes, such as eating smaller or less acidic meals if a person has reflux
  • antacids for acid reflux
  • ingredients to thicken food for people who have dysphagia because of neurological issues
  • swallowing therapy, a type of physical therapy, for people with dysphagia
  • drugs to expand the lower esophageal sphincter in people who have achalasia
  • an esophagogastroduodenoscopy (EGD), or upper endoscopy, to dilate the esophagus if the LES does not expand properly
  • Botox injections to help relax the LES in people who have achalasia

The sphincters of the esophagus act like doors that close and open based on the body’s needs. The muscles are not under voluntary control but can still become weak due to a wide range of health issues.

Esophageal sphincter dysfunction can be very painful, causing acid reflux, problems eating, and even malnourishment.

People who experience digestive issues or trouble swallowing should consult a doctor. Diagnosing the underlying cause may treat or even cure the symptoms of esophageal sphincter issues.