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.
Equine gastric ulcer syndrome
The stomach is divided into 2 main sections: a squamous region at the upper 1/3 of the stomach near the cardiac sphincter, and a lower glandular region. These 2 regions are separated by a band of tissue called the margo plicatus. The pH of the stomach contents varies by location. The most dorsal part of the stomach has the highest pH, usually close to 7, dropping to a pH of 3.0–6.0 near the margo plicatus, and reaching as low as 1.5–4.0 in the glandular regions. In foals, pH is uniform since all gastric contents are liquid, and pH rises for a around one hour after milk ingestion.