A student eats a protein-rich meal; plasma gastrin rises. Two hours later the meal has buffered poorly and the luminal pH of the gastric antrum falls below 2.5. Which mechanism suppresses further gastrin release?

• A Low pH directly depolarises G cells and blocks their calcium channels
• B Acid stimulates D cells to release somatostatin, which acts locally on G cells to inhibit gastrin secretion ✓
• C Acid triggers secretin release from S cells, which then degrades circulating gastrin
• D Acid denatures peptide fragments so that they can no longer stimulate G cells

Explanation

Antral acidification below about pH 3 is the dominant negative feedback on gastrin. Low luminal pH stimulates D cells in the antrum to release somatostatin, which diffuses through the local interstitium to adjacent G cells and, via Gi-coupled receptors, inhibits gastrin gene expression and secretion. This paracrine loop is blocked by proton pump inhibitors, which explains the hypergastrinaemia seen with their use. Secretin does not degrade gastrin.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.