FIGURE 1.

Biosynthesis and conjugation of BAs. Bile acids are primarily synthesized from cholesterol in the liver, by several enzymes, including CYP7A1 and CYP8B1 via an acidic or neutral pathway. Primary BAs are conjugated with taurine, glycine, or nonamino acid. Conjugated BAs are secreted into the bile duct and then enter the intestine via the major duodenal papilla. Most (95%) of BAs are reabsorbed in the terminal ileum and enter the enterohepatic circulation via the portal vein. The remainder will be converted to secondary BAs by bacteria in the colon and absorbed to the blood or discarded through feces. CA, cholic acid; DCA, deoxycholic acid, LCA, lithocholic acid.