Dietary lipids have low solubility. Bile salts act as detergents to emulsify them. Bile salts are synthesized in the liver and stored in the gallbladder. They are reabsorbed in the GI tract and transported back into the liver via enterohepatic circulation.
Cholesterol is modified via hydroxylation and carboxylation to increase solubility. 7 alpha hydroxylase is the rate limiting step. Cholic acid and chenodeoxycholic acid are primary bile acids. In the intestine, they are converted into deoxycholic and lithocholic acid via bacterial enzymes. These secondary acids are less soluble and so are easily excreted.
Bile salts can also be conjugated to glycine or taurine, lowering the pKa and making the bile salts better detergents.
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