Gastric acid
The main constituent of gastric acid is hydrochloric acid which is produced by parietal cells (also called oxyntic cells) in the gastric glands in the stomach. Its secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the hydrochloric acid is secreted into the lumen of the stomach. The pH of gastric acid is 1.5 to 3.5 in the human stomach lumen, the acidity being maintained by the proton pump H/K ATPase. The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide.
Infectious causes of cancer
"H. pylori" causes over 63% of all stomach cancers, which corresponds to more than 5.5% of all cancers in the world. As reviewed by Chang and Parsonnet, chronic "H. pylori" infection in the human stomach is characterized by chronic inflammation. This is accompanied by epithelial cell release of reactive oxygen species (ROS) and reactive nitrogen species (RNOS), followed by the assembly of activated macrophages at the stomach site of infection. The macrophages also release ROS and RNOS. Levels of 8-oxo-2'-deoxyguanosine (8-OHdG), one of the predominant forms of free radical-induced oxidative DNA damages, are increased more than 8-fold in DNA after infection by "H. pylori", especially if the "H. pylori" are cagA positive. The increase in 8-OHdG likely increases mutation. In addition, oxidative stress, with high levels of 8-OHdG in DNA, also affects genome stability by altering chromatin status. Such alterations can lead to abnormal methylation of promoters of tumor suppressor genes.