To understand why you have GERD you need to know about the normal workings of the esophagus, diaphragm and stomach. The first thing to understand is the action of normal swallowing. The only part of swallowing that we are normally conscious of happens at the back of the tongue and the throat. From the moment the food and drink reach the top of the esophagus, we are unaware of the rest of the process. Yet it is a very active one.

The esophagus is a muscular tube, and the muscles around it, along its length, coordinate their movements so that its contents are squeezed downwards, like emptying an inverted toothpaste tube from the base downwards to the nozzle.

Swallowing is not just the result of gravity. We transfer food towards the back of our throat using our tongue. Swallowing then becomes automatic, in that although we can feel the food slipping down towards the esophagus we cannot stop it from doing so. It is now under the control of the ‘autonomic nervous system’, a network of nerves that combine to control the movements of food through the rest of the gut, without our being aware of it.

When food hits the back of the throat (the pharynx) it stimulates two muscle reflexes: one shuts off the passages back into the mouth, the back of the nose and the lungs. The other squeezes the food down into the upper part of the esophagus. By doing this we can’t inhale and swallow at the same time. Food in the lungs is a disaster that can quickly lead to death.