The digestive system is set up to be a one-direction pathway: certain anatomical structures act as one-way valves along the way. One of these structures--the lower esophageal sphincter, or LES--is located at the end of the esophagus, just before the stomach. Its primary duty is to prevent the reflux, or backward flow, of gastric contents back up the esophagus, a condition known as gastroesophageal reflux disease, or GERD, commonly known as heartburn.
Lower Esophageal Pressure
The LES is a high-pressure zone, which contributes to its ability to prevent reflux. The LES muscle fibers, the diaphragm and pressure from the abdominal cavity contribute to the high pressure of the LES. When the pressure relaxes in the LES, gastric contents are able to reflux back into the esophagus. Causes of lower LES pressure include an overall loss of sphincter tone and inappropriate relaxations of the muscle. These inappropriate relaxations are triggered by gastric distension, according to Merck.com. Drugs such as antihistamines, antidepressents, calcium channel blockers, progesterone and nitrates can also lower LES pressure.
Hiatal Hernia
A hiatal hernia occurs when a part of the stomach slips up into the chest through an opening, or hiatus, in the diaphragm. The diaphragm is the muscle that separates the chest cavity from the abdominal cavity. HeartburnHelp.com notes that the diaphragm helps the LES by also contributing pressure around the esophagus to prevent reflux. When a portion of the stomach slips into the chest cavity and sits above the diaphragm, food and acid can reflux back into the esophagus. Obesity, pregnancy, coughing, vomiting or persistent straining to have a bowel movement can cause a hiatal hernia.
Diet and Exercise
The Mayo Clinic notes that fatty, spicy and fried foods can contribute to reflux. Because of their acidity, orange and tomato juices, as well as vinegar, can cause heartburn. According to the National Institute of Health, obesity, cigarettes and alcohol increase the risk of GERD. The obesity-GERD relationship is secondary to frequent gastric distension, which lowers LES pressure. Cigarette smoking and alcohol irritate and damage the LES.
References
- "Sabiston's Textbook of Surgery": The Biological Basis of Modern Surgical Practices; Courtney Townsend, M.D., et al.; 2008
- Heart Burn Help: Heartburn and GERD FAQs
- Mayo Clinic: Heartburn Risk Factors
- Merck: Gastroesophageal Reflux
- National Institute of Health: GERD
