O1i: Describe the composition, volume & regulation of intestinal secretions

Intestinal → Hormones, Alkalines, H2O

Composition

    • Alkaline mucous
    • GI hormones
    • Water

Function

  • Regulate digestion (hormones)
  • ↓gastric pH neutralisation (alkaline mucous)

Regulation

  • Alkaline → Vagus

Hormones

  • CCK
    • Peptides
    • CCK receptor agonist (GPCR) → ↑Ca2+
    • Contraction of GB
    • Regulate duodenal secretions
    • Satiety, Leptin release
    • ↑pancreatic enzyme (strong), ↑HCO3– (weak)
  • Secretin
    • Peptides (inc gastric inhibitory peptide)
    • Stimulated by ↓pH duodenum
    • 80% HCO3– secretion by pancreatic + biliary ducts
    • GIP released in response to CHO, Pr, fat → ↑insulin release & ↓gastric acid secretion
  • Motilin
    • Peptide
    • Fasting stimulates its cyclical release
    • ↑Migrating Myoelectric Complex of GI motility
    • Stimulates Pepsin production
    • Housekeeper of gut because improves peristalsis & prepares for next meal (i.e. erythromycin is a non-peptide motilin agonist)