The esophagus is the muscular tube that connects your throat to your stomach. When you swallow a bite of sandwich or a sip of water, it doesn't just fall down into your stomach by gravity. Instead, your esophagus squeezes in waves, pushing the food downward like toothpaste being squeezed from a tube. This wave-like motion is called peristalsis, and it's so effective that astronauts can swallow normally even in zero gravity.

The esophagus is about ten inches long in adults and sits behind your windpipe (the tube air travels through to your lungs). At the bottom, a special ring of muscle acts like a one-way valve, opening to let food into your stomach and then closing to keep stomach acid from splashing back up. When that valve doesn't work properly, people can get heartburn, which is caused by stomach acid irritating the esophagus.

You rarely think about your esophagus because it does its job automatically, but it's working hard with every meal you eat.