Fig. 5.

Enterohepatic circulation of bile acids. After each meal, gallbladder contraction empties bile acids into the intestinal tract. When passing through the intestinal tract, some bile acids are reabsorbed in the upper intestine by passive diffusion, but most bile acids (±95%) are reabsorbed in the ileum. Bile acids are transdiffused across the enterocyte to the basolateral membrane and excreted into portal blood circulation back to the liver. In the colon, secondary bile acids are formed by bacterial 7α-dehydroxylation of their primary bile acid precursor. Secondary bile acids may have a cytotoxic effect on the colonic epithelium. Bile acids lost in the feces (0.2–0.6 g/day) are replenished by de novo synthesis in the liver to maintain a constant bile acid pool. BA, bile acids; CA, cholic acid; CDCA, chenodeoxycholic acid; DCA, deoxycholic acid; LCA, lithocholic acid.