Stomach acid, more precisely known as gastric acid, is a secretion of the stomach used to break down food. It consists primarily of hydrochloric acid, with good amount of sodium chloride and potassium chloride as well. The acid has a pH of between 1 and 2, although at times in the process it is a bit higher. Stomach acid works in tandem with enzymes to break food down so that nourishment can be derived from it to help the body function, and so that the waste can be discarded. The acid made by the stomach is incredibly strong, so potent that undiluted it would burn through wood, and so the lining of the stomach itself has to be very tough to protect from being burned through.

The stomach contains cells called oxyntic cells, or parietal cells, which excrete stomach acid. This raises the acidity of the stomach drastically, which in turn interacts with food in the stomach. The stomach acid denatures the proteins present within food, exposing their peptide bonds. At the same time, stomach acid activates an important enzyme, pepsinogen, which is also secreted by the stomach. When it activates this enzyme it turns it into pepsin, which then breaks the bonds in proteins that link together the various amino acids, allowing these amino acids to be utilized.

In addition to helping to break down food, stomach acid also acts as a sort of safety mechanism to help protect your body against dangerous bacteria that may have been ingested with food or water. The highly acidic environment that gastric acid forms is deadly to the vast majority of harmful bacteria and other micro-organisms, helping to wipe out the bulk of intruders before your immune system even has to get involved. Although not a perfect defense, stomach acid helps reduce the workload on the body’s later defenses, and people with low stomach acid production often find themselves beset by micro-organisms and bacteria.

Once the stomach acid has done its job breaking down the food, splitting apart the amino acids, and denaturing the proteins, the resulting material is sent onward. The small and large intestines take this broken down material and absorb all of the vital nutrients that they can from it. Then, once processed as completely as it can be, the remainder is passed out of the body as waste.

When food passes into the stomach, it goes down a long tube called the esophagus. The esophagus has strong muscles at both ends, and the valve at the bottom is meant to stop stomach acid from making its way into the esophagus. Sometimes, however, this valve doesn’t do its job properly, and doesn’t keep all of the stomach acid out, allowing some to leak into the fragile esophageal tissue. When this happens, it is generally called heartburn, the sensation of burning from the acid in the tissue, and a taste of bile in the back of the throat.

Because stomach acid is so strong, the stomach has to have a defense mechanism to keep it from eating itself. This defense mechanism is in the form of a constant production of bicarbonate, which coats the layer of the stomach known as the mucosa. Bicarbonate is a base, and helps to neutralize the acid that touches the mucosa, keeping it contained within. Sometimes this mechanism doesn’t work properly, for a number of different reasons, including the bacteria Heliobacter pylori, extreme overproduction of acid, or a lack of sufficient blood supply. In this case, the stomach will in fact start eating itself, forming what is called a gastric ulcer.