Primary BAs are synthesized and conjugated in hepatocytes, and secreted into intestine to facilitate the fat digestion. Cyp7a1 is the rate-limiting enzyme for BA biosynthesis. Primary BAs are conjugated mainly with taurine in mice, by conjugating enzymes BAL and BAT. BAs are excreted into the canalicular bile by Bsep. In the intestinal lumen, BAs are transformed into secondary BAs by intestinal bacteria. BAs are efficiently reabsorbed by Asbt into ileocytes and effluxed into the portal blood by Ostα/β. Ntcp and Oatp1b2 take up BAs into hepatocytes. CA, CDCA, αMCA, and βMCA are the primary BAs in mice. DCA is the secondary BA of CA, LCA and UDCA are secondary BAs of CDCA, and ωMCA, MDCA, and HDCA are secondary BAs of α,βMCA.