What keeps food or fluid from going back up the esophagus to lungs?

The muscle that keeps food or fluid from going back up the esophagus to lungs is called the lower esophageal sphincter (LES). The LES is a circular muscle that surrounds the lower end of the esophagus, where it meets the stomach. When it is closed, it prevents stomach contents from flowing back into the esophagus. This is important because stomach acid can irritate the lining of the esophagus and cause a condition called gastroesophageal reflux disease (GERD).

The LES opens and closes in response to several factors, including the pressure in the stomach and esophagus, the presence of food or fluid in the esophagus, and the activity of the muscles in the abdomen. When you swallow, the LES relaxes to allow food or fluid to pass through. When you stop swallowing, the LES tightens to close off the esophagus.

In some people, the LES does not work properly and can allow stomach contents to flow back into the esophagus. This can cause GERD and other problems. There are a number of treatments for GERD, including medications, lifestyle changes, and surgery.