One of the layers of muscle runs up and down, while the other is circular. The oesophagus contracts in a wave-like manner from top to bottom (called peristalsis) in order to help food pass down to the stomach. Contraction of the circular muscle closes the oesophagus - this is why we are able to drink while standing on our heads. At the top of the oesophagus is a sphincter, which is normally closed to prevent us swallowing air as we breathe.
At the bottom of the oesophagus there is also a sphincter, which is designed to prevent the contents of the stomach from coming back up, because the lining of the oesophagus, unlike that of the stomach, cannot resist the acid that the stomach produces in order to digest food.
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