Composition
- Fluid produced by liver
- 95% water; same ionic composition as ECF
- 3% bile salts (in liver cholesterol \(\to\) bile acid \(\to\) bile salt)
- 1% phospholipid (prevents cholesterol precipitation)
- 0.5% cholesterol
- 0.2% conjugated bilirubin
- IgA
Storage
- 1L/day, continuous production by liver
- Stored in gallbladder, which actively reabsorbs Na \(\to\) H2O and Cl- follow secondarily \(\to\) concentrates bile.
Functions
- Increases surface area for digestion - bile salts are amphipathic \(\to\) subdivide lipid globules \(\to\) expose surface area for lipases
- Emuslifies fat \(\to\) micelles, allows absorption of lipids, cholesterol, and vitamins A, D, E, K ("ADEK").
- Excretion - of cholesterol, bilirubin, drugs, heavy metals
Regulation of delivery to duodenum
- Fats in duodenum \(\to\) I-cell releases CCK \(\to\) gallbladder contraction \(\to \ \uparrow\)delivery
- Acid in duodenum \(\to\) S-cell releases secretin \(\to\) increased alkaline bile secretion \(\to \ \uparrow\)delivery
- Cephalic phase \(\to\) Vagus releases ACh \(\to\) gallbladder contraction \(\to \ \uparrow\)delivery
- Catecholamines \(\to\) gall bladder relaxation \(\to \ \downarrow\)delivery