Bile salt synthesis occurs in the canalicular membrane of the hepatocyte, and in bile ductules or ducts. Conjugated bile salts are transported across the canalicular membrane by a carrier. The rate-limiting step in the hepatocellular transport of bile salts from the portal blood to the bile is at the canalicular membrane.
Functions of bile salts
Negative feedback role on their own rate of synthesis by inhibition of cholesterol 7 alpha-hydroxylase in the liver. Resecretion into bile.
Stimulate bile acid-dependent mechanisms: choleresis. Increase secretion of phospholipids.
Cholesterol solubilisation by incorporation into micelles. The stability of a solution of bile salts, lecithin and cholesterol can be shown in a triangular graph with an ordinate for each component of the micelle.
Emulsification of dietary lipid into micelles, increasing the surface area acces- X
c sible to lipid hydrolysing enzymes. i
Aid absorption of fat-soluble vitamins. P
Stimulate pancreatic secretion by releasing cholecystokinin-pancreozymin C
Inhibit pancreatic lipase.
Inhibit electrolyte and water absorption into the colon. Increase colonic motility.
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