22 Feb Gastric Acid Secretion and Its Regulation
Gastric Acid Secretion and Its Regulation
Gastric acid secretion is regulated by a complex interplay of neural, hormonal, and paracrine pathways. The primary stimuli include acetylcholine (ACh), gastrin, and histamine. Acetylcholine, released by the vagus nerve, directly stimulates parietal cells to secrete hydrochloric acid (HCl). Gastrin, produced by G cells in the antrum of the stomach, binds to CCK2 receptors on parietal cells and enterochromaffin-like (ECL) cells, prompting histamine release. Histamine, secreted by ECL cells, activates H2 receptors on parietal cells, enhancing acid production via the cyclic AMP pathway (Niv & Dickman, 2020). While gastric acidity is crucial for digestion and microbial defense, excessive acidity poses significant risks. Strong acidity can lead to mucosal injury, increasing the likelihood of gastritis, peptic ulcer disease (PUD), and gastroesophageal reflux disease (GERD). Chronic acid exposure can also contribute to Barrett’s esophagus, a precancerous condition. Furthermore, excessive acid can impair pancreatic enzyme function and nutrient absorption, exacerbating deficiencies in iron, calcium, and vitamin B12 (Feldman et al., 2022).
Pathophysiology of Helicobacter pylori
Helicobacter pylori (H. pylori) is a Gram-negative, spiral-shaped bacterium that colonizes the gastric mucosa, primarily in the antral region. It produces urease, an enzyme that hydrolyzes urea into ammonia and carbon dioxide, creating a local buffering environment that allows the bacteria to survive in the highly acidic stomach. Additionally, H. pylori adheres to gastric epithelial cells and induces an inflammatory response by releasing virulence factors such as cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA), leading to mucosal damage (Malfertheiner et al., 2021). The persistent inflammation can disrupt normal gastric physiology, increasing acid secretion in duodenal ulcers or leading to gastric atrophy and hypochlorhydria in chronic gastritis, increasing the risk for gastric cancer.
References
Feldman, M., Friedman, L. S., & Brandt, L. J. (2022). Sleisenger and Fordtran’s Gastrointestinal and Liver Disease: Pathophysiology, Diagnosis, Management. Elsevier.
Malfertheiner, P., Megraud, F., Rokkas, T., Gisbert, J. P., Liou, J. M., Schulz, C., & Wauters, T. (2021). Management of Helicobacter pylori infection: The Maastricht VI/Florence consensus report. Gut, 70(12), 2114-2132.
Niv, Y., & Dickman, R. (2020). Gastric acid secretion and its clinical implications: The role of histamine and gastrin. World Journal of Gastroenterology, 26(45), 7287-7301.
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