Secretin is released from S-cells in the duodenum. Which stimulus most potently triggers secretin release, and what is its primary physiologic action?
- A Duodenal fat (long-chain fatty acids); stimulates gallbladder contraction and Oddi relaxation
- B Gastric distension; inhibits gastric emptying via vagovagal reflex
- C Duodenal acidification (pH < 4.5); stimulates pancreatic HCO₃⁻-rich secretion to neutralize acid ✓
- D Protein digestion products (peptides); stimulates pancreatic enzyme secretion
Correct answer: C. Duodenal acidification (pH < 4.5); stimulates pancreatic HCO₃⁻-rich secretion to neutralize acid
Explanation
Acidic chyme entering the duodenum (pH < 4.5) is the primary stimulus for secretin release from S-cells. Secretin acts on pancreatic ductal cells (centroacinar cells) via cAMP to stimulate a large volume of HCO₃⁻-rich (but enzyme-poor) pancreatic juice, neutralizing duodenal acid to an optimal pH for pancreatic enzyme activity. CCK—not secretin—responds to fats and proteins to stimulate enzyme secretion and gallbladder contraction.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.