GI Hormones & Clinical Correlations: INBDE Review
Gastrin, secretin, CCK, GIP, motilin, and somatostatin: what each does, which cell makes it, and the clinical syndromes they reveal (Zollinger–Ellison, gallstones, incretin effect, octreotide use). 11 board-style MCQs.
Concept summary & clinical relevance.
Quick-reference structure first, then nerve-by-nerve detail. Mnemonics in amber, clinical pearls in blue.
GI hormones coordinate digestion: when to release acid, when to release bile, when to dump bicarbonate, when to release insulin in response to a meal. Each hormone has a single dominant action: learn the cell that makes it, the trigger, and the function. The clinical syndromes (Zollinger–Ellison, gallstone pain, incretin effect, octreotide indications) follow naturally.
| Hormone | Cell / source | Trigger | Main action |
|---|---|---|---|
| Gastrin | G cells (stomach antrum) | Peptides, distension, vagus | ↑ HCl from parietal cells; ↑ gastric motility |
| Secretin | S cells (duodenum) | Acidic chyme (low pH) | ↑ pancreatic HCO₃⁻; ↓ gastric acid |
| CCK | I cells (duodenum, jejunum) | Fatty acids, amino acids | Contracts gallbladder; ↑ pancreatic enzymes; slows gastric emptying |
| GIP | K cells (duodenum, jejunum) | Glucose, fats, amino acids | ↑ insulin (incretin effect); ↓ gastric acid |
| Motilin | Small intestine | Fasting state | Initiates migrating motor complexes (MMC) |
| Somatostatin | D cells (pancreas, GI mucosa) | Acid, broad GI activity | Universal inhibitor of GI hormones and secretions |
| Syndrome | Hormone abnormality | Key features |
|---|---|---|
| Zollinger–Ellison (gastrinoma) | ↑ Gastrin | Refractory peptic ulcers + diarrhea |
| Gallstone pain (biliary colic) | ↑ CCK in response to fatty meals | RUQ pain after fatty food |
| VIPoma (WDHA syndrome) | ↑ VIP | Watery Diarrhea, Hypokalemia, Achlorhydria |
| Carcinoid syndrome | Serotonin (and others) | Flushing, diarrhea: treated with octreotide |
Gastrin: turn on the acid
- Source: G cells in the stomach antrum.
- Triggers: dietary peptides, gastric distension, vagal stimulation (via gastrin-releasing peptide).
- Actions: stimulates parietal cells to release HCl; promotes gastric motility.
- Clinical: gastrinoma (Zollinger–Ellison) → recurrent peptic ulcers + diarrhea.
Secretin: neutralize the acid
- Source: S cells in the duodenum.
- Trigger: acidic chyme entering the duodenum.
- Actions: stimulates pancreatic HCO₃⁻ secretion to neutralize acid; inhibits gastric acid.
CCK: release bile + enzymes
- Source: I cells in the duodenum and jejunum.
- Triggers: fatty acids and amino acids in the duodenum.
- Actions: contracts the gallbladder, stimulates pancreatic enzyme secretion, slows gastric emptying.
- Clinical: a fatty meal triggers CCK release → gallbladder contraction → biliary colic if gallstones are present.
GIP, motilin, somatostatin
- GIP: from K cells; primary incretin: oral glucose stimulates more insulin than IV glucose because of GIP.
- Motilin: initiates the migrating motor complex during fasting; erythromycin is a motilin agonist (causes diarrhea side effect).
- Somatostatin: from D cells; inhibits virtually every GI and endocrine hormone. Octreotide is the synthetic analog used for variceal bleeding, VIPoma, carcinoid syndrome, and acromegaly.
11 board-style MCQs.
Active recall is the highest-yield study method for the INBDE. Pick an answer, check it, and read why every distractor is wrong, that's where the learning compounds.
The MCQs above are Core Recall, testing what you've memorized. The book adds a full Clinical Integration set: board-style patient scenarios where you apply this anatomy to real clinical reasoning. That's the section the INBDE actually weights heaviest.
- Question 1EasyWhich cell type secretes gastrin?
- Question 2EasyWhat is the main action of gastrin?
- Question 3ModerateWhich condition is caused by a gastrin-secreting tumor?
- Question 4EasyWhat is the primary effect of secretin?
- Question 5EasyWhich hormone contracts the gallbladder after a meal?
- Question 6ModerateWhich hormone slows gastric emptying after a fatty meal?
- Question 7ModerateWhich hormone is responsible for the “incretin effect”?
- Question 8ModerateWhich hormone stimulates migrating motor complexes during fasting?
- Question 9ModerateWhich antibiotic acts as a motilin agonist and can cause diarrhea or cramping?
- Question 10EasyWhich hormone is secreted by D cells and broadly inhibits GI hormones?
- Question 11ModerateWhich drug is a synthetic somatostatin analog used for variceal bleeding, VIPoma, carcinoid syndrome, and acromegaly?
900 INBDE-style MCQs with full explanations across 18 chapters — Core Recall plus board-style Clinical Integration scenarios — alongside Learning Summaries, Integration Bridges, and Review Boxes. Built by Dr. Isaac Sun for dental students who want to think like a clinician, not just memorize.
Founder, KYT Dental Services · Author, KYT INBDE series. These MCQs and Learning Summaries are part of a structural-thinking framework Dr. Sun uses with patients in the chair.