Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
Timeline of peptic ulcer disease and Helicobacter pylori
Before the 1950s, there were many microbiological descriptions of bacteria in the stomach and in gastric acid secretions, lending credence to both the infective theory and the hyperacidity theory as being causes of peptic ulcer disease. A single study, conducted in 1954, did not find evidence of bacteria on biopsies of the stomach stained traditionally; this effectively established the acid theory as dogma. This paradigm was altered when Warren and Marshall effectively proved Koch's postulates for causation of PUD by "H. pylori" through a series of experiments in the 1980s; however, an extensive effort was required to convince the medical community of the relevance of their work. Now, all major gastrointestinal societies agree that "H. pylori" is the primary nondrug cause of PUD worldwide, and advocate its eradication as essential to treatment of gastric and duodenal ulcers. Additionally, "H. pylori" has been associated with lymphomas and adenocarcinomas of the stomach, and has been classified by the World Health Organization as a carcinogen. Advances in molecular biology in the late 20th century led to the sequencing of the "H. pylori" genome, resulting in a better understanding of virulence factors responsible for its colonization and infection, on the DNA level.