composition
Last reviewed 01/2018
Bile is an isotonic fluid despite the presence of high concentrations of individual ions. This is because the micelles formed within bile act to bind ions and decrease their osmotic activity.
On average, bile is composed of:
- water; at least 90% per volume
- bile salts; 20-30mmol/l concentration
- bile pigments:
- 0.2-1 mmol/l
- by concentration, bilirubin diglucuronide >> monoglucuronide >> stercobilinogen
- electrolytes:
- sodium 140-165mmol/l
- potassium 3-6mmol/l
- chloride 80-115mmol/l
- bicarbonate 10-60mmol/l
- cholesterol; less than 3mmol/l
- phospholipids; 5-6mmol/l
- enzymes:
- alkaline phosphatase
- lactic dehydrogenase
- proteins:
- plasma proteins
- class A apoproteins
- IgA
- conjugated drugs for excretion
- conjugated hormones for excretion
- heavy metals e.g. copper
With passage through the biliary tree and gallbladder, water and bicarbonate ions are reabsorbed. Despite bicarbonate reabsorption, the pH of bile on entering the duodenum is on average greater than 7.6. This facilitates neutralization of gastric acidity.