O1i: Describe the Functions of Gastric Secretions
Composition
Slightly hyperosmotic 325mOsml/L
Higher K (10mmol/L), H+ (150mmol/L), Cl (180mmol/L)
Lower Na (2mmol/L)
Function
Digestive
- H2O
- Aid in the breakdown of food products and formation of chyme
- Pepsin (present as pepsinogen)
- Pepsinogen (proenzyme) produced by chief cells o Cleaved in gastric lumen
- Breaks down proteins (10% ingested protein)
- Gastric lipase
- Minimal activity
- Breaks down triglycerides and short chain FA
- Intrinsic Factor
- Produced by parietal cell
- Cofactor required for the absorption of Vit B12 in the terminal ileum
- Forms complex
Hormonal
- Gastrin
- Released from G cells in antrum
- Stimulates parietal cell HCl release (directly and via ↑histamine release from paracrine cells) → 1500 x more potent than histamine
- ↑GI/SI motility
- ↑pancreatic secretions
- ↑GB contraction
- Gastrin
Mucosal Protection
- Mucus
- Part of gastric protection
- Lines luminal surface of stomach
- Protects from autodigestion/ulceration (HCl, pepsin)
- Retains Na+, repels H+ o Lubrication of food
- Traps bacteria
- Bicarbonate
- Within mucus layer
- Aids in protection of luminal surface and buffers against autodigestion
- ↑pH close to surface (↓pepsin activity)
- Buffers H+ ions
Immunity
- HCl (pH 1.6)
- Produced by parietal cell
- Part of innate immunity → bacteriocidal
- Stimulates pancreatic and biliary secretions
- Provides optimal pH for pepsin activity
- aids ferric iron conversion to the more soluble ferrous ion
- HCl (pH 1.6)
Volume
2L/day
Regulation
3 phases: Gastric, Cephalic, Intestinal
Cephalic 30% gastric juice secretion
- Thought, sight, taste food
- Vagal stimulation
- Enteric nerves release
- Gastrin-Releasing Peptide → stimulates Gastrin secretion
- ACh → stimulates secretion of mucus, pepsinogen, HCl, HCO3-, H2O
Gastric 50% gastric juice secretion
- Entry of food into stomach
- Antral distention -> increases Gastrin secretion from G cells
- Gastrin/Histamine/ACh -> increase HCl secretion
- Acidic pH -> increase pepsinogen secretion
Intestinal 10% gastric juice secretion
- Acidic contents enter duodenum
- Somatostatin -> supresses gastrin release
- CCK -> decreases gastric emptying