Secretin Stimulates Pancreatic Bicarbonate Secretion
The correct answer is B - Secretin stimulates pancreatic enzyme secretion, though this requires clarification: secretin primarily stimulates bicarbonate-rich pancreatic fluid secretion rather than digestive enzymes. However, among the options provided, B is the most accurate, as secretin does have some effect on pancreatic secretion, particularly bicarbonate and fluid output 1, 2.
Primary Actions of Secretin
Secretin's main physiological role is stimulating bicarbonate-rich pancreatic fluid secretion, not digestive enzymes 1, 3, 2.
The hormone triggers secretion of bicarbonate from pancreatic ducts, bile ducts, and Brunner glands during the intestinal phase of digestion 4.
At physiological postprandial concentrations, secretin significantly increases pancreatic bicarbonate output but does not stimulate trypsin or lipase secretion 2.
Why the Other Options Are Incorrect
Option A (Stimulates Gastrin Secretion) - Incorrect
- Secretin does not stimulate gastrin secretion; gastrinomas are separate neuroendocrine tumors that autonomously secrete gastrin 5.
Option C (Inhibits Intestinal Motility) - Incorrect
- While secretin plays a role in coordinated gastrointestinal motor responses, it does not primarily function as an inhibitor of intestinal motility 6.
Option D (Stimulates Gastric Acid Secretion) - Incorrect
- Secretin does not stimulate gastric acid secretion; this is the role of gastrin 5.
Important Clarification on Enzyme Secretion
Secretin does NOT stimulate pancreatic digestive enzymes (trypsin, lipase) at physiological concentrations 2.
Only at supraphysiological doses does secretin produce a significant increase in pancreatic amylase secretion 2.
The primary enzyme-stimulating hormone is cholecystokinin (CCK), not secretin 1.
Clinical Context
Secretin works synergistically with CCK through hormone-hormonal and neural-hormonal interactions to regulate pancreatic secretion 1.
Secretin also functions in systemic bicarbonate homeostasis by activating renal bicarbonate excretion through receptors on beta-intercalated cells in the collecting duct 4.