The bile samples are isotonic with plasma, even though the total number of anions and cations is greater, as indicated by the dashed line. The rate limiting step is hydroxylation at the 7-alpha position. Conjugation causes a decrease in their pKa values, making them more water-soluble. The formation of bile salts is the main excretory pathway for cholesterol from the body. The enterohepatic cycling of bile salts increases during digestion and slows down between meals and during overnight fasting.
Bacteria also deconjugate bile salts.
Thus, removing the distal ileum decreases the rate of return of bile salts in the portal blood, resulting in a much greater rate of de novo bile-salt synthesis. Orally administered, bile salts cause an increase in the levels of bile salts in portal blood, and a greater degree of inhibition of bile-salt synthesis. The combination of bile salts and lecithin is better able to solubilize cholesterol. If the balance is disturbed, the bile may be in a state of cholesterol supersaturation. These vesicles, which are about 10X larger than micelles, and have phospholipid bilayers but contain no bile salts, are less stable and may fuse to form multilamellar aggregates from which solid cholesterol monohydrate crystals may nucleate and grow.