The liver produces about 500 to 600 mL of bile each day. Bile salts are synthesized in the hepatocytes from cholesterol. Bile salts are excreted into the bile and transported, to the intestine, via the intra- and extrahepatic bile ducts.
Bile consists of ∼95% water in which are dissolved a number of endogenous solid constituents including bile salts, bilirubin phospholipid, cholesterol, amino acids, steroids, enzymes, porphyrins, vitamins, and heavy metals, as well as exogenous drugs, xenobiotics and environmental toxins.
Bile salts are the major organic solutes in bile and normally function to emulsify dietary fats and facilitate their intestinal absorption. Bile salts function as essential surfactants used to solubilize dietary fats in the hydrophilic milieu of gut.
These functions, and the complex metabolism undergone by bile salts, all take place in the context of the enterohepatic circulation and depend on its proper functioning. The enterohepatic circulation may be thought of as an endless flow of detergent through the liver, biliary tract, small and to some extent large, intestine, and back to the liver again.
Bile salts represent potent signaling molecules in liver and intestine: in the small intestine, they strengthen the defense against microbes by farnesoid X receptor (FXR)-dependent mechanisms and modulate hepatobiliary bile formation by FXR-controlled ileal release of the peptide hormone fibroblast growth factor 19.
Bile salts at low concentrations stimulate pancreatic triacylglycerol lipase (PTL) activity, but higher concentrations inhibit PTL activity. Pancreatic triacylglycerol lipase activity is regulated by colipase that interacts with bile salts and PTL and can release bile salt mediated PTL inhibition. Without colipase, PTL is unable to hydrolyze fatty acids from dietary triacylglycerols, resulting in fat malabsorption with severe consequences on bioavailability of dietary lipids and fat-soluble vitamins.
Bile salts are efficiently recycled via the portal system back to the liver in the so-called enterohepatic circulation.
Bile salts are 24 carbon water soluble products of cholesterol metabolism. Two primary bile salts are synthesized in mammalian liver: cholic acid, a trihydroxylated bile salt, and chenodeoxycholic acid (CDCA), a dihydroxy bile salt. Each can be conjugated at the side chain with either taurine or glycine.
What are the functions of bile salt in human body?
