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Here's your rapid-study sheet on Gastric Secretion - everything from your pages, exam-optimized:
🧠 GASTRIC SECRETION - RAPID NOTES
BASICS (1 liner)
- Stomach secretes 1,200-1,500 mL/day of gastric juice at pH 3
- Secreted from glands in stomach wall + surface cells
STOMACH FUNCTIONS (quick list)
| Function | Key Point |
|---|---|
| Excretory | Alkaloids & toxins expelled via stomach |
| Endocrine | Secretes hormones: Gastrin, Somatostatin D, Histamine (ECL cells) |
| Reflex | Gastro-salivary, gastroileal, gastrocolic reflexes |
| Regulation | Food in stomach triggers pancreatic juice + bile secretion |
3 PHASES OF GASTRIC SECRETION ⭐
Phase 1 - CEPHALIC (30% of juice)
Trigger: Sight/smell/thought of food - BEFORE food enters stomach
Pathway: Sight/smell → Cerebral cortex + Amygdala/Hypothalamus → Vagus nerve (from dorsal median nucleus) → Submucosal plexus of ENS → Gastric juice secreted
Memory trick: "CEPHalic = CEPHal = HEAD" → triggered by head senses
Phase 2 - GASTRIC (60% of juice) ⭐ BIGGEST
Trigger: Food enters stomach, stretches walls
Pathway:
- Stretching → excites myenteric + vagovagal reflexes
- Hormones secreted: Gastrin + Histamine
- Lasts 3-4 hours while food remains in stomach
Memory trick: "GASTRIC phase = most juice (60%) = in the STOMACH"
Phase 3 - INTESTINAL (10% of juice)
Trigger: Food enters duodenum (upper intestine)
- Small amounts of gastrin secreted → stimulates 10%
- Beyond duodenum: Secretin, CCK, GIP released → INHIBIT gastric secretion
- Enterogastric reflex also inhibits secretion
Memory trick: "Intestine INHIBITS - only 10%"
CELLS & WHAT THEY SECRETE ⭐ (High yield!)
| Cell | Secretion |
|---|---|
| Parietal cells (fundus/body) | HCl + Intrinsic Factor (IF) |
| Chief cells | Pepsinogen + Gastric lipase |
| Surface mucus cells | Mucus + Bicarbonate (mucus-bicarbonate layer) |
| Enteroendocrine cells | Gastrin, Somatostatin, Serotonin |
MECHANISM OF HCl SECRETION ⭐ (Short note topic!)
Gastrin → secreted from G cells of stomach → HCl secreted via Parietal cells → stimulates secretion of Histamine
Step by step:
- CO₂ from metabolism + H₂O → H₂CO₃ (enzyme: carbonic anhydrase)
- H₂CO₃ → HCO₃⁻ + H⁺
- HCO₃⁻ exchanges with Cl⁻ in blood capillaries → raises blood/urine pH = "Postprandial Alkaline Tide" ⭐
- H⁺ is actively exchanged for K⁺ at apical membrane via H⁺-K⁺ ATPase pump
- H⁺ + Cl⁻ → HCl in canaliculi (water enters by osmosis)
- Final HCl concentration: 150-160 mEq/L
WHY ISN'T STOMACH SELF-DIGESTED? ⭐ (Exam favorite!)
- Mucus-bicarbonate layer protects stomach wall
- Pepsinogen only activated by acid (not pre-activated)
- Parasympathetic/acid stimulates pepsinogen release via local enteric reflexes
- If mucosa is irritated → more mucus is secreted (protective)
CASTLE'S INTRINSIC FACTOR (CIF) ⭐
- Secreted by parietal cells
- Combines with Vitamin B12 → CIF-B12 complex
- Required for absorption at terminal ileum
- Deficiency (atrophic gastritis / partial gastrectomy) → Pernicious Anemia
- Features: Megaloblastic anemia + Peripheral neuropathy
GASTRIC MOTILITY (1 liner)
- Food enters via LES (gastroesophageal sphincter)
- Intraluminal pressure at LES = 30 mmHg
- Tonic constriction of LES prevents acid reflux
⚡ EXAM CHEAT SHEET - % Numbers to Remember
| Phase | % Juice |
|---|---|
| Cephalic | 30% |
| Gastric | 60% |
| Intestinal | 10% |
- Gastric juice: 1200-1500 mL/day, pH 3
- HCl concentration: 150-160 mEq/L
- LES pressure: 30 mmHg
- Gastric phase lasts: 3-4 hours
🔑 SHORT NOTE TOPICS (write these confidently)
- Phases of gastric secretion - 3 phases + %, triggers
- Mechanism of HCl secretion - carbonic anhydrase pathway + postprandial alkaline tide
- Castle's Intrinsic Factor - pernicious anemia link
- Why stomach doesn't self-digest - mucus-bicarbonate barrier
- Gastrin - from G cells, stimulates HCl via parietal cells
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