Category: biosynthesis
Hepatic conversion of cholesterol to primary bile acids (cholic acid + chenodeoxycholic acid). Classic pathway: cholesterol → 7α-hydroxycholesterol via CYP7A1 (rate-limiting, FXR-regulated). Alternative pathway: cholesterol → 27-OH-cholesterol via CYP27A1 (relevant in extrahepatic tissues). Primary bile acids conjugate with glycine or taurine before biliary secretion. In the intestine, bacterial 7α-dehydroxylase converts primary bile acids to secondary (deoxycholic + lithocholic acid). FXR feedback closes the loop: enterohepatic bile acid return → ileal FGF19 → hepatic FXR → CYP7A1 suppression.