The esophagus is part of the gastrointestinal system. It is a tube that connects the mouth to the stomach and is between 9 and 10 inches long. When it is relaxed, it is only about an inch wide.
The esophagus is found right behind the trachea, or the windpipe. It has four layers of tissue and two sphincters, or structures that are able to be opened and closed. The top sphincter opens when the person is swallowing so food can travel to the stomach. There's another sphincter at the bottom of the esophagus to keep food from returning from the stomach. However, this sphincter can weaken, and the acidic contents of the stomach can flow back into the esophagus. This is known as acid reflux and can develop into a condition known as gastroesophageal reflux disease.
When a person eats and swallows, the food simply doesn't drop down the esophagus into the stomach. It is moved by muscle contractions known as peristalsis. Peristalsis allows the esophagus to grow wider to accommodate the food and make sure it gets into the stomach. This mechanism is so powerful that it works even when a person is standing on his head.
On the other hand, the esophagus allows a person to vomit when he or she has eaten a toxic or distasteful substance. Vomiting is the opposite of peristalsis.