GI Hormones Overview - Gut Feeling Orchestrators
- GI hormones: Peptide messengers from enteroendocrine cells (EECs) in GI mucosa & pancreas. Regulate digestion, absorption, motility, gut growth.
- Key Sites: Stomach (G cells), Duodenum (I, S, K cells), Jejunum, Pancreas (islets).
- Action Modes:
- Endocrine: Bloodstream to distant targets (e.g., Gastrin, CCK).
- Paracrine: Local diffusion to nearby cells (e.g., Somatostatin).
- Neurocrine: Neuronal release (e.g., VIP, GRP).
⭐ Zollinger-Ellison syndrome, marked by severe peptic ulcers, arises from a gastrin-secreting tumor (gastrinoma), often pancreatic.
Gastrin & CCK - Acid & Bile Bosses
| Hormone | Source | Stimulus | Main Actions | Clinical Note |
|---|---|---|---|---|
| Gastrin | G cells (stomach antrum, duodenum) | Peptides, amino acids, distension, vagal (GRP) | ↑ HCl secretion (parietal cells), ↑ Mucosal growth (trophic effect) | Zollinger-Ellison Syndrome (gastrinoma) |
| CCK | I cells (duodenum, jejunum) | Fatty acids (>10C), amino acids (Trp, Phe) | ↑ Pancreatic enzyme & HCO₃⁻, ↑ Gallbladder contraction, ↓ Gastric emptying, Sphincter of Oddi relaxation | Gallbladder function test (ejection fraction) |
⭐ CCK is the principal stimulus for delivery of pancreatic enzymes and bile into the small intestine.
Secretin Family & Incretins - Pancreatic Juice & Sugar Supervisors
| Hormone | Source | Stimulus | Main Actions | Clinical Note |
|---|---|---|---|---|
| Secretin | S cells (duo) | Acid (pH < 4.5), fats | ↑ Pancreatic $HCO_3^-$; ↓ Gastric acid | ZES test (paradoxical ↑ gastrin) |
| GIP | K cells (duo,jej) | Glucose, fats, AAs | ↑ Insulin (Incretin); ↓ Gastric acid | Oral > IV glucose insulin |
| VIP | Enteric nerves | Neural | ↑ Intestinal secretion ($H_2O$, electrolytes); Relax smooth muscle | VIPoma: WDHA syndrome |
| GLP-1 | L cells (ile,col) | Glucose, fats, AAs | ↑ Insulin, ↓ Glucagon, ↓ Gastric empty, ↑ Satiety (Incretin) | Agonists for T2DM/obesity |
Motility & Satiety Hormones - Movers, Shakers & Appetite Breakers
| Hormone | Source | Stimulus | Main Actions |
|---|---|---|---|
| Motilin | M cells (duodenum, jejunum) | Fasting, alkaline pH | ↑ GI motility (MMC initiator), ↑ gastric emptying |
| Ghrelin | P/D1 cells (gastric fundus) | Fasting, hypoglycemia | ↑ Appetite (orexigenic), ↑ GH release, ↑ gastric emptying |
| Somatostatin | D cells (pancreas, GI) | Acid, fat, protein, neural | ↓ GI motility, ↓ secretions (universal inhibitor), ↓ splanchnic blood flow |
| Peptide YY | L cells (ileum, colon) | Postprandial fat, carbs | ↓ Appetite (anorexigenic), ↓ gastric emptying, ↓ GI motility |
High‑Yield Points - ⚡ Biggest Takeaways
- Gastrin (G cells): Stimulates HCl secretion; ↑ in Zollinger-Ellison syndrome.
- CCK (I cells): Triggers pancreatic enzyme release, gallbladder contraction; ↓ gastric emptying.
- Secretin (S cells): Promotes pancreatic HCO₃⁻ secretion to neutralize acid.
- Somatostatin (D cells): Universal inhibitor of GI secretions & motility.
- GIP (K cells): Enhances insulin release (incretin effect).
- Motilin: Initiates migrating motor complexes (MMCs) during fasting.
- Ghrelin (stomach): Stimulates hunger.
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