All About All of the Sphincters in Your Body

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Sphincters are special, circular muscles that open and close certain body parts. Most often, the sphincter regulates the passage of some type of fluid, such as bile, urine, or fecal matter.

The action of sphincters may happen involuntarily through the autonomic nervous system or maybe under some voluntary control through the somatic nervous system.

If a sphincter loses muscle tone or has too much tone (spasticity), symptoms and illness can follow. This can include urinary retention, in which the bladder can't empty completely. Sphincter issues can also cause bladder and fecal incontinence, or the inability to control the bladder or bowels.

This article discusses some of the different sphincters in the body, where they're located, and what they do.

Acid reflux due to improper closure of sphincter
BSIP / UIG / Getty Images

Digestive System Sphincters

There are six different sphincters within the digestive system.

Upper Esophageal Sphincter

The upper esophageal sphincter (UES) is also known as the inferior pharyngeal sphincter. It can be found at the end of the pharynx (throat). It protects the entrance to the esophagus, which carries food from your throat to your stomach.

The UES prevents air from getting into the esophagus when you breathe. It also prevents you from breathing food into your respiratory tract.

Because of its location, the UES also plays a role in burping and vomiting. Malfunctioning of the UES, as part of gastroesophageal reflux disease (GERD), can cause acid to back up into the throat or into the airways.

Lower Esophageal Sphincter

The lower esophageal sphincter (LES), also known as the cardiac sphincter, is located at the bottom of the esophagus where it meets up with the stomach.

It lets food pass from the esophagus into the stomach and allows air to escape from the stomach when burping. It also prevents stomach acid from washing back up into the esophagus. A malfunction of the LES is one of the primary causes of GERD.

Recap

The upper esophageal sphincter prevents air from getting into the esophagus and keeps food from going into your respiratory tract. The lower esophageal sphincter lets air come up from the stomach when burping and usually keeps stomach acid out of the esophagus.

Pyloric Sphincter

The pyloric sphincter is located between the stomach and the duodenum, which is the first part of the small intestine.

The pyloric sphincter opens to allow partially digested food (chyme) to pass from the stomach into the duodenum. This allows for further digestion and absorption of nutrients into the body.

Sphincter of Oddi

Sphincter of Oddi (SO) is located where the common bile duct and the pancreatic duct connect to the duodenum. The common bile duct is a tube that carries bile into the duodenum. The pancreatic duct carries digestive enzymes to the duodenum.

The SO opens after you've eaten to allow bile from the gallbladder and enzymes from the pancreas to enter the duodenum. This breaks down food components for absorption into the body.

Sphincter of Oddi dysfunction (SOD) happens when this sphincter doesn't work correctly. This causes a backup of bile and pancreatic enzymes. A relatively rare disorder, it can cause episodes of pain in the chest area.

Ileocecal Sphincter

The ileocecal sphincter is located where the small intestine and the large intestine meet. There is not much known about this sphincter. However, it is thought to expel chyme from the end of the small intestine (the ileum) into the large intestine.

Anal Sphincter

The anal sphincter is located at the end of the rectum, and therefore at the end of the digestive tract. The anal sphincter regulates the process of the evacuation of stool. It has both an inner and outer component.

The inner sphincter is under involuntary control and therefore prevents stool from leaking out. The outer sphincter is predominantly under voluntary control and allows for a bowel movement. A malfunction of the anal sphincter can cause stool leakage, a health condition known as fecal incontinence.​

Recap

The inner part of the anal sphincter keeps stool from leaking out. The outer portion allows you to have a bowel movement.

Other Sphincters

There are other sphincters that you have throughout your body.

Urethral Sphincter

Also known as the sphincter urethrae, this sphincter controls the holding and emptying of urine. Like the anal sphincter, the urethral sphincter has both inner and outer muscles. The inner muscle has involuntary control and the outer muscle has voluntary control.

Iris Sphincter

The iris sphincter is also known as the pupillary sphincter or sphincter pupillae. This sphincter regulates the closing of the pupil in the eye.

Summary

The body's sphincters are circular muscles that open and close certain parts of the body. Sphincters in the digestive tract open to allow food, bile, or digestive enzymes to go from one part of the body to another.

In some cases, the sphincter may not function correctly. This can cause symptoms or illness. For instance, if the lower esophageal sphincter doesn't work right, it can let stomach acids into the food pipe, leading to GERD.

Sphincters are in other parts of the body as well. They include the urethral sphincter, which can control the flow of urine, and the iris sphincter, which can constrict your pupils.

Frequently Asked Questions

  • What is a sphincter?

    Sphincters are circular muscles that serve as valves to open and close certain parts of the body. 

    For example, the digestive system has several sphincters that regulate the passage of fluid and food from the mouth to the stomach, through the intestines, and out the anus. In the eye, the pupillary sphincter in the iris opens and closes to regulate the amount of light it lets in. 

  • How many sphincters are there in the human body?

    A lot. There are at least 50 or 60 different types of sphincters in the human body. Some are microscopic, such as the millions of precapillary sphincters in the circulatory system. Some are controlled involuntarily by the autonomic nervous system, some respond to certain stimuli, and others we control directly.

    The anus has two sphincters, an internal involuntary sphincter and an external voluntary sphincter that we control.

  • What health problems are related to sphincters?

    Sphincter muscles can become weak or damaged, resulting in health conditions. In gastroesophageal reflux disease (GERD), the lower esophageal sphincter muscle relaxes at the wrong time. This allows stomach acid to flow up the esophagus, causing acid reflux. If the anal sphincter is weak and damaged, it can cause fecal incontinence. 

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6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
  • Minocha A, Adamec C. The Encyclopedia of the Digestive System and Digestive Disorders (2nd Ed.) New York:Facts on File. 2011.

  • Mittal RK. Upper esophageal sphincter. in: Motor Function of the Pharynx, Esophagus, and its Sphincters. San Rafael (CA): Morgan & Claypool Life Sciences; 2011.