Bile Secretion

Overview

• Bile
  • necessary for digestion and absorption of lipids in gastrointestinal system
  • synthesized and secreted by liver, stored in gallbladder
• Bile composition
  • bile salts
    • synthesis
      • cholesterol → primary bile acids → secondary bile acids → bile salts
    • conjugation
      • liver conjugates bile acids with amino acids (glycine, taurine) to form bile salts
      • conjugation changes pKs of bile acids, increasing water solubility
    • function
      • emulsification of dietary lipids
      • formation of micelles with products of lipid digestion
  • bile pigments
    • e.g., bilirubin
  • cholesterol
  • phospholipids
  • electrolytes (aka ions)
• water

Bile Secretion

• Secretory pathway
  • cholecystokinin (CCK)
    • stimulates (1) contraction of gallbladder and (2) relaxation of sphincter of Oddi 
      • bile flows gallbladder → duodenum
        • bile emulsifies and solubilizes dietary lipids in small intestine