University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

133

Pages:

3
Author:

Mariam A. A.

• Gastric Secretion Principal exocrine secretions in the stomach are: o Digestive proenzymes – pepsinogen by the chief (peptic) cells o Hydrochloric acid (HCl) and gastric intrinsic factor secreted by parietal (oxyntic) cells ▪ GIF is needed for vitamin B12 absorption Why are we using drugs to inhibit or neutralise gastric acid secretion? • Principal clinical indications for reducing acid secretion are: o Peptic ulceration: duodenal and gastric o Gastroesophageal reflux disease (GORD): gastric juices cause damage to oesophagus Protection of the surface cells of the stomach • Mucus-secreting cells in the gastric mucosa • Bicarbonate ions secreted and trapped in mucus creating a gel-like protective barrier that maintains the mucosal surface at a pH of 6-7 in the face of a much more acidic environment (pH 1-2) in the lumen • Locally produced 'cytoprotective' prostaglandins stimulate the secretion of both mucus and bicarbonate • Disturbances in these secretory and protective mechanisms are thought to be involved in the pathogenesis of peptic ulcers, and the therapy of this condition includes drugs that modify each of these factors Genesis of peptic ulcers • Imbalance between the mucosal-damaging (acid, pepsin) and the mucosal-protecting agents (mucus, bicarbonate (neutralises acid), prostaglandins E2 and I2, NO) o NO → vasodilation → increased bicarbonate supply as it is taken from blood • Often caused by an infection of the gastric mucosa with Helicobacter pylori Phases of gastric secretion Regulation of acid secretion • Principal stimuli acting on parietal cells to secrete acid are: o Gastrin (stimulatory hormone) o ACh (stimulatory neurotransmitter) o Histamine (stimulatory local hormone) • Prostaglandins E2 and I2 inhibit acid secretion o Hence COX inhibitors contribute to stomach ulcers • ACh and histamine are both small molecules, gastrin is a peptide (larger) Mechanism of hydrochloric acid secretion by the parietal cells • The secretion of the parietal cells is an isotonic solution of HCl (150 mmol/l) with pH < 1 • H+ is exported by the proton pump