A brief tour of the anatomy of the stomach and esophagus will help you understand what causes acid reflux disease. Think of the esophagus as an upright sausage that connects to the stomach at the lower end and throat at the upper end. It is narrowed at both the bottom and top by two contracting muscles known as sphincters. The lower esophageal sphincter (LES) is at the bottom in an area called the gastroesophageal junction. The upper esophageal sphincter (UES) is at the top, adjacent to the throat. When one swallows, the esophageal sphincters must temporarily relax and open, allowing food to travel to the stomach.
As soon as food passes through the sphincters, they must tighten back up. Both gravity and peristalsis (a coordinated series of muscle contractions in the esophagus) help food move in the proper direction, from high to low.
If the LES doesn't tighten closed after food passes from the esophagus into the stomach, acid from the stomach can flow back up into the esophagus, resulting in gastroesophageal reflux disease (GERD). Pepsin, an enzyme produced by the stomach, accompanies the refluxed acid. Bile acids from the first part of the intestines — the duodenum — are also occasionally refluxed with the stomach acid.
Similarly, if the UES doesn't tighten closed after food passes from the throat to the esophagus, the caustic gastric contents can travel all the way up into the throat, resulting in laryngopharyngeal reflux disease (LPRD).
Acid reflux occurs when the normal mechanisms keeping acid in the stomach are disrupted. This can be caused by changes in LES pressure, peristalsis and intragastric pressure, or pressure within the stomach. Reflux occurs when the pressure is high enough to overcome the pressure at the gastroesophageal junction, forcing the LES to open. The most common example of this is abdominal obesity. Intragastric pressure can also increase when the stomach doesn't empty normally. This is known as delayed gastric emptying. It is common in pregnancy, but may also occur with certain medications (such as opioid painkillers) and in people with certain diseases (such as diabetes).
Situations that relax the LES itself can cause acid reflux. Tobacco is one of the most potent and common relaxers of the LES. Various medications, such as antidepressants and certain asthma medications, may also cause relaxation of the sphincter and thereby lead to acid reflux. Tobacco smoking also relaxes the UES, which is one reason why it can also produce symptoms of LPRD.
Anatomic abnormalities around the gastroesophageal junction can also interfere with normal functioning of the LES. A prime example of this is a hiatus hernia, which is a condition in which part of the stomach is located in the chest instead of the abdomen. This causes the LES to close poorly, promoting acid reflux.
Impaired Esophageal Peristalsis
Even if acid flows from the stomach to the esophagus, it may cause no problems if the amount is small and if peristalsis in the esophagus is normal. When peristalsis is impaired — a condition called esophageal dysmotility — acid that is refluxed back into the esophagus will not be promptly pushed back into the stomach. It therefore stays in the esophagus, causing damage.
What’s Special About Laryngopharyngeal Reflux Disease?
Since the esophagus is connected to the stomach, the cells lining the lower part of the esophagus have adapted so they can tolerate small amounts of acid exposure. However, the lining of the throat and larynx, which are far removed from the stomach, are far more sensitive to even tiny amounts of acid, which can easily cause damage to the throat.
Saliva is one of the natural ways the body has to protect itself against acid. It generally contains large amounts of bicarbonate, which is a basic substance that can neutralize acids. If the production of salivary bicarbonate is reduced, such as by tobacco smoking, the neutralizing effects of saliva will also be reduced. This can further predispose to acid reflux disease, especially LPRD.
Pepsin plays an important role in causing LPRD. When pepsin is refluxed up from the stomach into areas above the esophagus, such as the vocal cords, lungs, sinuses and middle ear, it can remain in these areas for quite awhile. Pepsin becomes activated in acidic environments. So if a person consumes food or liquid that is very acidic, pepsin in these areas will become activated and cause inflammation. Therefore, with LPRD, it's not only what comes up from the stomach that may be irritating the body, but also the activated pepsin that is residing in these areas.