Gastric Juices

Gastric acid is a digestive fluid, formed in the <a href="http://en.wikipedia.org/wiki/Stomach" title="Stomach">stomach</a>. It has a <a href="http://en.wikipedia.org/wiki/PH" title="PH">pH</a> of 1.5 to 3.5 and is composed of <a href="http://en.wikipedia.org/wiki/Hydrochloric_acid" title="Hydrochloric acid">hydrochloric acid</a> (HCl) (around 0.5%, or 5000 <a href="http://en.wikipedia.org/wiki/Parts_per_million" title="Parts per million" class="mw-redirect">parts per million</a>), and large quantities of <a href="http://en.wikipedia.org/wiki/Potassium_chloride" title="Potassium chloride">potassium chloride</a> (KCl) and <a href="http://en.wikipedia.org/wiki/Sodium_chloride" title="Sodium chloride">sodium chloride</a> (NaCl).

The acid plays a key role in digestion of <a href="http://en.wikipedia.org/wiki/Proteins" title="Proteins" class="mw-redirect">proteins</a>, by activating <a href="http://en.wikipedia.org/wiki/Digestive_enzymes" title="Digestive enzymes" class="mw-redirect">digestive enzymes</a>, and making ingested proteins unravel so that digestive enzymes can break down the long chains of <a href="http://en.wikipedia.org/wiki/Amino_acids" title="Amino acids" class="mw-redirect">amino acids</a>.

Gastric acid is produced by cells lining the stomach, which are coupled to systems to increase acid production when needed.

Other cells in the stomach produce <a href="http://en.wikipedia.org/wiki/Bicarbonate" title="Bicarbonate">bicarbonate</a>, a base, to <a href="http://en.wikipedia.org/wiki/Buffering_agent" title="Buffering agent">buffer</a> the fluid, ensuring that it does not become too acidic. These cells also produce <a href="http://en.wikipedia.org/wiki/Mucus" title="Mucus">mucus</a>, which forms a viscous physical barrier to prevent gastric acid from damaging the stomach. Cells in the beginning of the small intestine, or <a href="http://en.wikipedia.org/wiki/Duodenum" title="Duodenum">duodenum</a>, further produce large amounts of bicarbonate to completely neutralize any gastric acid that passes further down into the digestive tract.

The presence of gastric acid in the stomach and its function in digestion was first characterized by U.S. Army surgeon <a href="http://en.wikipedia.org/wiki/William_Beaumont" title="William Beaumont">William Beaumont</a> around 1830. Beaumont was able to study the stomach action of fur trapper <a href="http://en.wikipedia.org/wiki/Alexis_St._Martin" title="Alexis St. Martin">Alexis St. Martin</a> due to the latter's gastric <a href="http://en.wikipedia.org/wiki/Fistula" title="Fistula">fistula</a>.

In <a href="http://en.wikipedia.org/wiki/Hypochlorhydria" title="Hypochlorhydria" class="mw-redirect">hypochlorhydria</a> and <a href="http://en.wikipedia.org/wiki/Achlorhydria" title="Achlorhydria">achlorhydria</a>, there is low or no gastric acid in the stomach, potentially leading to problems as the <a href="http://en.wikipedia.org/wiki/Disinfectant" title="Disinfectant">disinfectant</a> properties of the gastric lumen are decreased. In such conditions, there is greater risk of infections of the <a href="http://en.wikipedia.org/wiki/Digestive_tract" title="Digestive tract" class="mw-redirect">digestive tract</a> (such as infection with <a href="http://en.wikipedia.org/wiki/Vibrio" title="Vibrio">Vibrio</a> or <a href="http://en.wikipedia.org/wiki/Helicobacter" title="Helicobacter">Helicobacter</a> bacteria).

In <a href="http://en.wikipedia.org/wiki/Zollinger%E2%80%93Ellison_syndrome" title="Zollinger–Ellison syndrome">Zollinger–Ellison syndrome</a> and <a href="http://en.wikipedia.org/wiki/Hypercalcemia" title="Hypercalcemia" class="mw-redirect">hypercalcemia</a>, there are increased <a href="http://en.wikipedia.org/wiki/Gastrin" title="Gastrin">gastrin</a> levels, leading to excess gastric acid production, which can cause <a href="http://en.wikipedia.org/wiki/Gastric_ulcer" title="Gastric ulcer" class="mw-redirect">gastric ulcers</a>.

In diseases featuring excess vomiting, patients develop <a href="http://en.wikipedia.org/wiki/Chlorine" title="Chlorine">hypochloremic</a> <a href="http://en.wikipedia.org/wiki/Metabolic_alkalosis" title="Metabolic alkalosis">metabolic alkalosis</a> (decreased blood acidity by <a href="http://en.wikipedia.org/wiki/Hydrogen" title="Hydrogen">H</a>+ and <a href="http://en.wikipedia.org/wiki/Chlorine" title="Chlorine">chlorine</a> depletion).