Normal Bile — A Balanced Ternary Solution
Healthy bile keeps cholesterol dissolved inside bile salt micelles.
- ~800 mL: Bile produced per day (by hepatocytes)
- 2: Cholesterol carriers (micelles and vesicles)
- ~3 g: Bile salt pool (recycled ~6×/day)
- <1.0: Normal saturation index (undersaturated bile)
The bile solubility triangle
Cholesterol needs bile salts and phospholipids to stay soluble.
Micelle transport
Mixed micelles shuttle cholesterol safely through watery bile.
Enterohepatic recycling
Bile salts are reabsorbed in the ileum and reused.
Cholesterol Supersaturation Begins
Excess liver cholesterol overwhelms the available bile salt supply.
- >1.0: Cholesterol saturation index (supersaturated bile)
- ~3×: Risk multiplier, obesity (higher hepatic cholesterol output)
- ↑ secretion: Estrogen effect (pregnancy, oral contraceptives)
- up to 30%: Rapid weight loss risk (develop gallstones)
Hepatic hypersecretion
The liver pumps out more cholesterol than bile salts can hold.
Gallbladder stasis
Poor emptying lets supersaturated bile linger and concentrate.
Common risk factors
Obesity, rapid weight loss, and estrogen raise cholesterol output.
Cholesterol Monohydrate Crystal Nucleation
Dissolved cholesterol precipitates into microscopic crystal seeds.
- Monohydrate: Crystal type (plate-like cholesterol crystals)
- Pro-nucleating: Mucin gel role (traps crystal nuclei)
- Days–weeks: Nucleation time (before first stone visible)
- >70% cholesterol: Stone composition (defines a cholesterol stone)
Vesicle aggregation
Cholesterol-rich vesicles fuse and crystallize out of solution.
Pro-nucleating factors
Mucin glycoproteins accelerate crystal formation in stagnant bile.
From crystal to stone
Crystals clump together and slowly enlarge into a stone.
Hemolysis or Infection Drives Pigment Stones
Excess bilirubin binds calcium and precipitates as dark pigment.
- Hemolysis / infection: Trigger (sickle cell, cirrhosis, biliary infection)
- Sterile: Black stones (from chronic hemolysis)
- Infected: Brown stones (bacterial deconjugation of bilirubin)
- β-glucuronidase: Key enzyme (unmasks free bilirubin)
Bilirubin overload
Hemolysis floods bile with unconjugated bilirubin pigment.
Calcium binding
Free bilirubin binds calcium to form an insoluble salt.
Infection route
Bacterial enzymes deconjugate bilirubin, seeding brown pigment stones.
A Mature Gallstone Has Formed
Aggregated crystals harden into a single solid gallstone.
- ~10–15%: Prevalence (of adults worldwide)
- ~80%: Cholesterol stones (of all gallstones)
- ~20%: Pigment stones (black and brown types)
- ~20%: Symptomatic rate (of stone carriers)
Cholesterol stone outcome
Yellow-green, layered stones dominate in Western populations.
Pigment stone outcome
Small, dark, brittle stones dominate hemolytic patients.
Clinical significance
Stones can obstruct the cystic or common bile duct.