Bile is isosmotic with plasma and consists primarily of water and electrolytes but also organic compounds: bile salts, phospholipids (mostly lecithin), cholesterol, bilirubin, and other endogenously produced or ingested compounds, such as proteins that regulate GI function and drugs or their metabolites.
In the intestine, bile salts function as essential surfactants used to solubilize dietary fats in the hydrophilic milieu of gut.
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
salt function in digestion
