In this introduction to acid reflux and GERD, here I want to quickly explain what the sphincter is and it’s role in helping deal with GERD and acid reflux symptoms.

At the cardia, just where the esophagus becomes the stomach, there is a ring of muscle around it, within its wall. Imagine a bicycle inner tube that is semi-inflated with an elastic band around it, gripping it a little and narrowing it. Then transfer that image to the esophagus as the inner tube, and the sphincter muscles as the elastic band.

Sphincters exist at crucial areas of the gut where it is important for there to be no back-flow. The first sphincter in the line between mouth and anus is the one between the esophagus and the stomach, at the cardia. The next is at the pylorus, where the food passes from the stomach into the duodenum. The third is where the contents of the small bowel (the ileum) enter the large bowel (the caecum), so it is called, fairly obviously, the ileo-caecal sphincter. The last is between the rectum and anus, the anal sphincter. That’s the one that helps to make us sociable human beings: it allows us to refuse the natural call to pass a motion.

To return to the gastro-esophageal sphincter. The angle at which the esophagus meets the stomach, as mentioned above, is important in preventing reflux. However, so is the efficiency of the sphincter at the same site. It opens (in other words, the muscle of the sphincter relaxes) to let food and drink pass from esophagus to stomach, and it closes  to prevent the food flowing back from  stomach to esophagus. It is a one-way valve that normally works perfectly.

As well as the sphincter muscles themselves, there is another group of muscles that keeps this valve structure intact. These are the obliquely positioned muscles that keep the esophagus and stomach at the appropriate angle to each other, much like a sling or hammock. Without these muscles, the angle between esophagus and stomach would flatten out and the bottom end of the esophagus would open in a straight line full on to the stomach. That would make back-flow very much easier.

Such back-flow pressures mount up when the stomach, full of food, starts its job of digestion. Like the esophagus, the stomach wall has peristaltic waves flowing through it, which propel the food from above downwards, towards the outlet at the pyloric sphincter into the duodenum. However, it is also subject to chaotic churning waves of muscle activity that are helpful in mixing the stomach contents thoroughly with the digestive juices. If the gastro-esophageal sphincter and the oblique muscle fibers are not working properly and together, this may allow the chaotic waves to push the stomach contents backwards, up into the lower esophagus – and this is acid reflux, and the start of GERD.