Bile

Composition

• Water: ~97% (primary component).
• Solutes
  • Bile salts (aka bile acids, 50%): Most abundant solute. Amphipathic derivatives of cholesterol. Emulsify fats for digestion; absorb fat-soluble vitamins (A, D, E, K).
  • Phospholipids (40%): Primarily lecithin. Solubilize cholesterol; prevent cholesterol gallstones.
  • Cholesterol (4%): Bile is the primary route of cholesterol excretion from the body.
  • Bilirubin (2%): Pigment derived from heme catabolism. Gives bile its color. Excreted in bile.
  • Water & Electrolytes: Make up the bulk of bile volume. Gallbladder concentrates bile by absorbing water.

---

Enterohepatic Circulation

• Mechanism: ~95% of bile salts are reabsorbed in the Terminal Ileum via Na⁺-bile acid cotransporters and recycled to the liver via the portal vein.
  • Primarily reabsorb bile salts, and few of cholesterol
• Clinical Correlation:
  • Crohn’s Disease / Ileal Resection: Damage to the terminal ileum prevents bile salt reabsorption.