Acid reflux is the backward flow of the acidic stomach contents (food + acid + other secretions) up into the esophagus. It is not uncommon for every healthy person to experience acid reflux occasionally but in certain cases, this retrograde flow may become persistent or recurrent. Prolonged exposure to the stomach acid irritates or damages the lining of the esophagus (esophagitis) and causes a range of signs and symptoms that are collectively referred to as gastroesophageal reflux disease (GERD, GORD ~ UK).
What prevents acid reflux?
The passage of contents between the stomach and esophagus is regulated by the lower esophageal sphincter (LES). It is a thickening of the muscular esophageal wall that remains contracted tonically to prevent reflux. The LES is further supported by the muscles of the diaphragm. During swallowing , the muscles relax and the sphincter opens thereby allowing food and drink to pass from the esophagus into the stomach. Retrograde flow is prevented by the sphincter’s ability to remain contracted at a pressure that can withstand the forceful stomach contractions during digestion.
As illustrated in the diagram above, stomach acid is constantly churned with food in the stomach. This is essential for chemical digestion. The strong muscle contractions also physically breaks up food in the stomach (mechanical digestion). This creates significant pressure within the stomach. Eventually small amounts of the stomach chyme passes through the pyloric sphincter into the duodenum.
However if the lower esophageal sphincter is compromised or the pressure within the stomach is greater than that caused by the muscle contraction of the sphincter, then the stomach acid will pass up into the esophagus.
Acid in the Esophagus
The stomach is developed to withstand the effects of gastric acid by secreting a mucus layer which acts as a buffer between the acid and the stomach lining. The duodenum (first part of the small intestine) also has mechanisms to handle the incoming acidic gastric contents. The pancreas secretes bicarbonate ions and water which neutralize the acidic chyme in the duodenum plus secretin, a digestive hormone, decreases the secretion of acid in the stomach as well as slowing stomach emptying.
The esophagus however, is not as competent in dealing with stomach acid. In the odd case of acid reflux, peristaltic waves (esophageal motility) will quickly push the acidic contents back into the stomach. Large amounts of alkaline saliva may be secreted which is then swallowed and neutralizes any remnants of stomach acid in the esophagus. These measures were not specifically developed in the human body just to deal with stomach acid. However, the body’s ability to compensate for any irregularity in the short term means that most cases of the odd acid reflux incident will not cause damage to the esophagus or lead to symptoms.