All about all the sphincter muscles in your body

Sphincter muscles are special, round muscles that open and close certain body parts. In most cases, the sphincter muscle regulates the passage of certain fluids, such as bile, urine, or feces.

Actions of the sphincter may occur involuntarily through the autonomic nervous system or under some voluntary control through the somatic nervous system.

Symptoms and disease can occur if the sphincter muscle loses muscle tone or becomes overtonic (spasm). This may include urinary retention, in which the bladder cannot be completely emptied. Sphincter problems can also lead to bladder and fecal incontinence, or inability to control the bladder or bowel.

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

digestive system sphincter

There are six different types of sphincter muscles in the digestive system.

upper esophageal sphincter

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

UES prevents air from entering the esophagus when you breathe. It also prevents you from breathing food into your airways.

Because of its location, the UES also plays a role in hiccups and vomiting. UES failure is part of gastroesophageal reflux disease (GERD), which can cause acid to reflux into the throat or airways.

Upper Esophageal Sphincter and Acid Reflux

lower esophageal sphincter

The lower esophageal sphincter (LES), also known as the cardia sphincter, is located where the bottom of the esophagus meets the stomach.

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It allows food to enter the stomach from the esophagus and allows air to escape from the stomach when burping. It also prevents stomach acid from flowing back into the esophagus. LES failure is one of the main causes of GERD.


The upper esophageal sphincter prevents air from entering the esophagus and prevents food from entering the airways. The lower esophageal sphincter muscle lets air out of the stomach when burping, usually keeping stomach acid away from the esophagus.

pyloric sphincter

The pyloric sphincter is located between the stomach and duodenum and 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

The sphincter of Oddi (SO) is located where the common bile and pancreatic ducts join the duodenum. The common bile duct is the tube that carries bile to the duodenum. The pancreatic duct transports digestive enzymes to the duodenum.

SO opens after you eat, allowing 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) occurs when the sphincter doesn’t work properly. This causes a backup of bile and pancreatic enzymes. A relatively rare disorder that can cause attacks of chest pain.

Sphincter of Oddi Anatomy and Function

ileocecal sphincter

The ileocecal sphincter is located at the junction of the small and large intestines. Little is known about this sphincter. However, chyme is thought to be excreted from the end of the small intestine (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 defecation. It has internal and external components.

The internal sphincter is under involuntary control and thus prevents fecal leakage. The external sphincter is mainly under voluntary control and allows defecation. Anal sphincter dysfunction can lead to fecal leakage, a health condition called fecal incontinence.​


The inside of the anal sphincter prevents stool from leaking out. The outside allows you to defecate.

Anal sphincter anatomy and function

other sphincter

You have other sphincter muscles throughout your body.

urethral sphincter

Also called the urethral sphincter, this sphincter controls the retention and emptying of urine. Like the anal sphincter, the urethral sphincter also has inner and outer muscles. Internal muscles have involuntary control and external muscles have voluntary control.

iris sphincter

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


The body’s sphincter muscles are round muscles that open and close certain parts of the body. The sphincter muscles in the digestive tract open to allow food, bile, or digestive enzymes to flow from one part of the body to another.

In some cases, the sphincter may not work properly. This can lead to symptoms or illness. For example, if the lower esophageal sphincter is not working properly, it can allow stomach acid to enter the food pipe, causing gastroesophageal reflux.

Sphincter muscles are also present in other parts of the body. They include the urethral sphincter, which controls the flow of urine, and the iris sphincter, which contracts the pupil.

Frequently Asked Questions

  • What is a sphincter?

    Sphincter muscles are round muscles that act as valves to open and close certain parts of the body.

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

  • How many sphincter muscles are there in the human body?

    a lot of. There are at least 50 or 60 different types of sphincter muscles in the human body. Some are microscopic, such as the millions of pre-capillary sphincter muscles in the circulatory system. Some are involuntarily controlled by the autonomic nervous system, some are in response to certain stimuli, and some are under our direct control.

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

  • What health problems are related to the sphincter?

    The sphincter muscles can become weak or damaged, leading to health conditions. In gastroesophageal reflux disease (GERD), the lower esophageal sphincter 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 lead to fecal incontinence.