Protein digestion

protein → [pepsin :: stomach] → polypeptides → [trypsin, chymotrypsin :: duodenum] → oligopeptides → [carboxypeptidase, aminopeptidase]

therefore

  • first stage = stomach
  • final stage = brush border of small intestine
    • Amino acids are transported across the epithelial membrane (i.e. enter the cell) via secondary active transport (co-transport) with Na+ ions
    • Amino acids cross the basal membrane (get out to the blood) by facilitated diffusion

transport across cell membranes in intestines

Lumen → intracellular: co-transport with Na+
Basal membrane → blood: facilitated diffusion

#gastrointestinal

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