Above is a fluorescent micrograph of hepatocytes, the bile producing and secreting cells of the liver.
Bile is a digestive fluid produced in hepatocytes cells of the liver, stored in the gall bladder, and secreted into the duodenum (the most anterior portion of the small intestine). Understanding how bile breaks down fats is directly linked to it’s chemical structure and composition.
Bile is primarily composed of water, but the key solutes are called bile salts.
How are these bile salts synthesized? With excess cholesterol in the liver, hepatocytes synthesize two key primary bile acids: cholic acid and chenodeoxycholic acid. When the hydroxyl groups on these acids are cleaved by the activity bacteria in the small intestine, Cholic acid is converted to deoxycholic acid and chenodeoxycholic acid to lithocholic acid. Any of these bile acids can be bonded with the amino acids taurine and glycine to yield an amphipathic conjugated form (one side hydrophobic and the other hydrophillic), which is known as a bile salt.
The process of bile salt formation requires 17 different enzymes and spans several regions of individual cells. It is important to note that "the genes encoding several of the enzymes of bile acid synthesis are under tight regulatory control to ensure that the necessary level of bile acid production is coordinated to changing metabolic conditions.”
Bile is a fat emulsifier, meaning that it breaks apart fats. This process, however, is not enzymatic. As previously mentioned, bile salts contain one side derived from cholesterol (hydrophobic/lipid soluble) and the other from an amino acid (hydrophilic/water soluble). This chemical composition allows bile to break apart fat globules to even smaller droplets, increasing the surface area of the fats and thus increasing absorption by the small intestine.
Connexin Microscopy Gallery
Bile Acid Synthesis and Utilization, The Medical Biochemistry Page
Proteomic Analysis of Bile, Annarita Farina, Jean-Marc Dumonceau, Pierre Lescuyer