Free cholesterol is virtually insoluble in aqueous solutions, but in bile, it is made soluble by bile acids and lipids like lethicin. Gallstones , most of which are composed predominantly of cholesterol, result from processes that allow cholesterol to precipitate from solution in bile. Role of Bile Acids in Fat Digestion and Absorption Bile acids are derivatives of cholesterol synthesized in the hepatocyte. The cholesterol portion of a bile acid is hydrophobic and the amino acid conjugate is polar and hydrophilic. Emulsification is not digestion per se, but is of importance because it greatly increases the surface area of fat, making it available for digestion by lipases, which cannot access the inside of lipid droplets.
Bile acids are also critical for transport and absorption of the fat-soluble vitamins .
Role of Bile Acids in Cholesterol Homeostasis Hepatic synthesis of bile acids accounts for the majority of cholesterol breakdown in the body. In humans, roughly 500 mg of cholesterol are converted to bile acids and eliminated in bile every day. This route for elimination of excess cholesterol is probably important in all animals, but particularly in situations of massive cholesterol ingestion . Interestingly, it has recently been demonstrated that bile acids participate in cholesterol metabolism by functioning as hormones that alter the transcription of the rate-limiting enzyme in cholesterol biosynthesis. Enterohepatic Recirculation Large amounts of bile acids are secreted into the intestine every day, but only relatively small quantities are lost from the body.