To better understand why you have GERD or acid reflux, and what you can do to cure it, we need to look at the role of your esophagu to help give us some clues for finding effective treatments and remedies and hopefully get rid of those acid reflux symptoms once and for all.

The esophagus is a very muscular tube. The action of the autonomic nerves causes it to contract and relax in a very controlled to anus, and are the means by which food, and then faeces, are passed onwards. If peristalsis fails, the food simply sticks where it is lying. Liquid may trickle downwards, but solids will stay in a lump, stretching the tube walls and causing serious discomfort.

Three types of muscle contractions make up the peristaltic process:

1. Once we start to swallow, primary peristaltic waves ripple down the esophagus, pushing food in front of them at a rate of 5 centimeters a second.
2. If the primary peristaltic waves don’t manage to empty the contents of the esophagus into the stomach, a secondary wave starts, about halfway down the esophagus. This reinforces the primary wave, and sometimes it can be felt as an uncomfortable, almost indescribable, feeling, deep in the chest. It is a main symptom in many acid reflux cases, and readers with GERD will almost certainly recognize it.
3. Radiologists categorize a third form of muscle contraction in the esophagus, which they describe as ‘tertiary’ when they are watching the progress of barium swallow studies. They occur in one segment of esophagus at a time. They don’t appear to be involved in swallowing, and don’t propel food forwards. We don’t know why they appear. One suggestion is that they are a way of keeping the esophageal muscles in tone between meals, while waiting for the next lump of food to come down.

Peristalsis is vital for transferring solid and semi-solid food from the back of the throat into the stomach. If we are upright, liquids can trickle down the esophagus by themselves. Once we swallow a liquid, as long as there is no obstruction to its flow, it enters the stomach by gravity alone. However, peristalsis is needed to ensure that fluids won’t return up from the stomach into the throat. Without it, if you swallowed a drink when lying flat, or even upside down, the drink or food would flow back into the mouth.

My colleagues and I in my year at medical school have graphic memories of being taught about swallowing. One of our physiology lecturers (a particularly excellent doctor), brought into the lecture hall a pint of beer, climbed on to the demonstration table, stood on his head facing us, then drank the beer in one go. He didn’t find it difficult and didn’t spill a drop. Unfortunately he declined to perform an encore!

So the rippling muscles of the esophagus ensure that the passage of food and drink through it is one-way only. This is very important. If food travels in the other direction you are sick - vomiting - and you feel awful with it.

At its lower end the esophagus passes through a hole - in Latin, this is the hiatus - in the diaphragm, a sheet of muscle that separates the contents of the chest from the organs in the abdomen. Below the diaphragmatic hiatus, the esophagus becomes the upper part of the stomach. How it does so, and how the stomach and esophagus relate to the diaphragm, are crucial to understanding GERD.

It is vital that the one-way flow of food through the esophagus is continued when it reaches the stomach. Once in the stomach, it has to stay there for a while to allow mixture of the food with the stomach’s digestive juices, and then pass forward into the duodenum, the first part of the small bowel. The stomach’s digestive juices are very acid so that they can break down proteins (mainly meats and fish) into their constituent parts, before being taken up through the small bowel wall into the body. The stomach wall is largely protein, so it would digest itself if it weren’t protected against its own juices.

That protection takes two forms. There are four main types of ’secreting’ cells in the stomach lining. One provides the acid (hydrochloride acid) that initiates protein breakdown. Another provides the pepsin that digests the proteins even further. A third provides a thick mucus that spreads over the whole of the stomach lining to protect it from acid attack. The fourth secretes bicarbonate that neutralizes excess acid, adding more protection against self-digestion.

At the lower end of the stomach the bicarbonate secretion begins to predominate, so that the duodenum receives a mixture of semi digested food at a much less acid level - almost neutral - than the material in the main body of the stomach. When the protective mechanisms of mucus and bicarbonate break down or are diminished, the stomach does start to self-digest, leading to ulcers - exposed areas of stomach lining that are inflamed and eroded.

Stomach ulcers are usually due to a failure of the balance between the stomach’s digestive secretions and its self protection mechanisms. They are often called ‘peptic’ ulcers because the combination of pepsin and acid is a powerful cause of erosion of the underlying stomach wall.

Understanding this balance between digestive secretions and self protection is vital if you need to understand what is going on in GERD. If the acid and pepsin of the stomach somehow finds its way upwards into the lower esophagus, the balance between digestion and protection has gone. The cells that line the esophagus do not secrete a mucus protection or bicarbonate: they offer no protection at all against the acid and pepsin.

So if acid and pepsin enter the esophagus there is an immediate reaction. The cells respond with irritation and inflammation, and the brain interprets this as heartburn and pain. If the process continues for more than a few hours, ulcers form in the lower end of the esophagus; and when they eventually heal, they may do so with scarring that can narrow it. Long exposure of the esophagus to the stomach’s secretion can eventually lead to multiple scarring, bleeding and even perforation of the esophagus, complications that are obviously dangerous and life-threatening.

It’s crucial for normal health, therefore, that we keep the stomach contents out of the esophagus. The body tries its best to do so, using several mechanisms working together in mutual co-operation. They are the cardia, the sphincter and the diaphragm. Knowing how each of them contributes to keeping stomach juices out of the esophagus is essential to understanding what may produce acid reflux or GERD.