## Regulation of Gastric Acid Secretion ### Somatostatin's Dual Inhibitory Role: **Key Point:** Somatostatin (released by D cells) is the primary inhibitor of gastric acid secretion and acts at multiple levels: 1. **Direct inhibition of parietal cells:** Somatostatin receptors on parietal cells inhibit H⁺ secretion 2. **Inhibition of gastrin secretion:** Somatostatin acts on G cells to suppress gastrin release 3. **Inhibition of histamine release:** Somatostatin suppresses ECL cell histamine secretion ### Why Other Options Are Wrong: **Option 0 (Gastrin release):** Gastrin is released in response to: - Amino acids and peptides (protein digestion) - Gastric distension - Increased intragastric pH (>3.0) — NOT decreased pH - Fatty acids INHIBIT gastrin release (via secretin and cholecystokinin) **Option 2 (Secretin):** Secretin is released when duodenal pH <3.0 and acts to: - INHIBIT gastric acid secretion (not enhance) - Stimulate pancreatic bicarbonate secretion - Inhibit gastric motility **Option 3 (Acetylcholine):** ACh acts on multiple cells: - M3 receptors on parietal cells → H⁺ secretion - M3 receptors on G cells → gastrin release - M3 receptors on D cells → somatostatin release **Mnemonic:** **"SOS" (Somatostatin Opposes Secretion)** — somatostatin inhibits acid, gastrin, and histamine.
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.