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.