Stomach acid is the collection of gastric secretions secreted by the lining of the stomach and contained with the stomach cavity. It is a combination of hydrochloric acid (HCl), pepsin and intrinsic factor and due to the presence of HCl, the overall pH of the solution is low meaning that it is acidic.
The stomach secretes about 1.5 liters of juices per day which includes digestive enzymes, mucus and water. Every liter of stomach secretions (juices) contain about 160 millimoles of HCl resulting in a pH of 1 to 2, although it can be as low as 1.8 or as high as 3.
Stomach acid is necessary for digestion because it chemically breaks down foods. The acidity also activates other digestive enzymes which contribute to chemical digestion as well. Apart from its role in digestion, the stomach acid is the first major line of defense against invading microorganisms that enter the gut with food or drink.
The production of stomach acid and the stimulation and inhibition of its secretion is discussed further under Gastric Acid.
Stomach Acid Protection
The stomach lining has its own innate protective mechanism to withstand the stomach acid. A layer of mucus secreted by the stomach epithelium protects the stomach cells from the corrosive acid.
Even the duodenum, the first part of the small intestine, has mechanisms to deal with acid entering from the stomach. Water and alkaline bicarbonate ions are secreted by the pancreas and enters the duodenum where it neutralizes the stomach acid. Digestive hormones secreted when acidic chyme enters the duodenum also slows normal stomach emptying and decreases gastric secretions.
The esophagus, however, does not have any such protective mechanism. When the lower esophageal sphincter (LES), which restricts the back flow of stomach acid into the esophagus, fails to function effectively, the esophagus is exposed to the stomach acid and becomes inflamed. In some cases, the stomach acid can rise as far up as the throat, enter the airways or even reach the nasal cavity.
Stomach Acid Problems
A change in the pH or volume of the normal stomach acid secretions can affect the digestive function (refer to Digestive Problems) or damage the surrounding parts of the alimentary tract.
Low Stomach Acid
Hypochlorhydria or achlorhydria is when there is little or no stomach acid. This does not mean that there is no gastric secretions. Rather the quantity (volume) of the acid is lower than norm or the pH of the solution is higher than norm thereby making the stomach acid less acidic (higher pH).
Conditions associated with low stomach acid, either as a result of volume or acidity (pH), includes :
- Stomach cancer (gastric carcinoid tumors)
- Recurrent stomach infections
- Malabsorption syndromes
- Small intestinal bacterial overgrowth
Excess Stomach Acid
Hyperchlorhydria is when the volume of stomach secretions are higher than normal or the pH of the stomach secretions are lower than normal thereby making it more acidic. It is also known as hyperacidity.
Conditions associated with excess stomach acid, either as a result of volume or acidity (pH), includes :
Stomach Acid Reflux
Gastroesophageal reflux disease (GERD or GORD) is the backflow of stomach acid up into the esophagus. It is also commonly known as acid reflux. This can be severe to the extent that it can reach the throat. Stomach acid reflux may be due to an excess in the stomach secretion volume, however, other factors like LES incompetence are also contributing factors.
Other conditions associated with stomach acid reflux includes :