Somatostatin secreted by D cells of the gastric antrum limits acid secretion. Which stimulus most directly triggers its release, and what is its principal mode of action?
- A Luminal pH below about 3; it acts in a paracrine manner to inhibit G cells, ECL cells and parietal cells ✓
- B Luminal amino acids; it directly stimulates parietal cells to secrete buffer
- C Vagal cholinergic input; it potentiates histamine release from enterochromaffin-like cells
- D Duodenal fat; it enters the systemic circulation and suppresses pancreatic enzyme output
Correct answer: A. Luminal pH below about 3; it acts in a paracrine manner to inhibit G cells, ECL cells and parietal cells
Explanation
Antral D cells sense luminal acidity directly; when pH falls below roughly 3 they release somatostatin, which diffuses locally to suppress gastrin release from G cells, histamine release from ECL cells and acid secretion by parietal cells. This is a negative feedback loop protecting against excessive acidity. Vagal activity actually inhibits D cells via mediators that reduce somatostatin release, removing option C.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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