What is the pyloric sphincter?

The stomach contains something called the pylorus, which connects the stomach to the duodenum. The duodenum is the first section of the small intestine. Together, the pylorus and duodenum play an important role in helping to move food through the digestive system.

The pyloric sphincter is a band of smooth muscle that controls the movement of partially digested food and juices from the pylorus into the duodenum.

The pyloric sphincter is located where the pylorus meets the duodenum.

Explore the interactive 3-D diagram below to learn more about the pyloric sphincter.

The pyloric sphincter serves as a kind of gateway between the stomach and the small intestine. It allows the contents of the stomach to pass into the small intestine. It also prevents partially digested food and digestive juices from reentering the stomach.

The lower parts of the stomach contract in waves (called peristalsis) that help to mechanically break down food and mix it with digestive juices. This mixture of food and digestive juices is called chyme. The force of these contractions increases in the lower parts of the stomach. With each wave, the pyloric sphincter opens and allows a little bit of chyme to pass into the duodenum.

As the duodenum fills, it puts pressure on the pyloric sphincter, causing it to close. The duodenum then uses peristalsis to move the chyme through the rest of the small intestine. Once the duodenum is empty, pressure on the pyloric sphincter goes away, allowing it to open again.

Bile reflux

Bile reflux happens when bile backs up into the stomach or esophagus. Bile is a digestive liquid made in the liver that’s usually found in the small intestine. When the pyloric sphincter doesn’t work properly, bile can make its way up the digestive tract.

The symptoms of bile reflux are very similar to those of acid reflux and include:

  • upper abdominal pain
  • heartburn
  • nausea
  • green or yellow vomit
  • cough
  • unexplained weight loss

Most cases of bile reflux respond well to medications, such as proton pump inhibitors, and surgeries used to treat acid reflux and GERD.

Pyloric stenosis

Pyloric stenosis is a condition in infants that blocks food from entering the small intestine. It’s an uncommon condition that tends to run in families. Around 15% of infants with pyloric stenosis have a family history of pyloric stenosis.

Pyloric stenosis involves a thickening of the pylorus, which prevents chyme from passing through the pyloric sphincter.

Symptoms of pyloric stenosis include:

  • forceful vomiting after feeding
  • hunger after vomiting
  • dehydration
  • small stools or constipation
  • weight loss or problems gaining weight
  • contractions or ripples across the stomach after feeding
  • irritability

Pyloric stenosis requires surgery to create a new channel that allows chyme to pass into the small intestine.


Gastroparesis prevents the stomach from properly emptying. In people with this condition, the wave-like contractions that move chyme through the digestive system are weaker.

Symptoms of gastroparesis include:

  • nausea
  • vomiting, especially of undigested food after eating
  • abdominal pain or bloating
  • acid reflux
  • sensation of fullness after eating small amounts
  • fluctuations in blood sugar
  • poor appetite
  • weight loss

In addition, certain medications, such as opioid pain relievers, can make symptoms worse.

There are several treatment options for gastroparesis, depending on the severity:

  • dietary changes, such as eating several smaller meals per day or eating softer foods
  • controlling blood glucose levels, either with medication or lifestyle changes
  • tube feeding or intravenous nutrients to make sure the body gets enough calories and nutrients

The pyloric sphincter is a ring of smooth muscle that connects the stomach and small intestine. It opens and closes to control the passage of partially digested food and stomach juices from the pylorus to the duodenum. Sometimes, the pyloric sphincter is weak or doesn’t work properly, leading to digestive problems, including bile reflux and gastroparesis.