What is the biochemical reason why bile secretion is important for health?

Micelles are made up of amphipathic compounds such as bile acids, fatty acids and monoacylglycerols that interact leaving a relatively stable hydrophilic surface and hydrophobic interior (1). They form at certain temperature ranges when a mixture of lipids is present in concentrated amounts (1). Fatty acid and phospholipid micelles are spherical, but pure bile acid micelles are sandwich-shaped rectangles (1p1062).

During lipid digestion after hydrolysis of triacylglycerols by lipases, it’s up to the bile acid sandwiches to solubilize the spheres, thereby forming “mixed” micelles that appear not unlike rods (1p1062). These rods become longer as more lipids (including limited cholesterol) are solubilized (1p1062). The bile acid micelles form at concentrations of 2-5 mM and at pH values above pK, meaning in equilibrium with other micelles in solution (1p1061-2).

From the lumen, the micelles then transfer the lipids to the mucosal surface for absorption by diffusion (1p1063). Lipid-soluble vitamins A, D, E, and K are also transported within the micelles (1p1065). The delivery is dependent on bile acid micelles increasing effective concentration to create solute flux across the unstirred fluid layer (1p1063). Without bile acids, the absorption of triacylglycerols and the lipid-soluble vitamins would be reduced drastically (1p1063).

Reference List

1. Devlin TM. Textbook of Biochemistry with Clinical Correlations. Philadelphia: Wiley-Liss, 2002.

Published by David Despain, MS, CFS

David is a science and health writer living on Long Island, New York. He's written for a variety of publications including Scientific American, Outside Online, the American Society for Nutrition's (ASN) Nutrition Notes Daily, and Institute of Food Technologists' (IFT) Food Technology magazine and Live! blog. He's also covered new findings reported at scientific meetings including Experimental Biology, AAAS, AOCS, CASW, Sigma Xi, IFT, and others on his personal blog "Evolving Health." David is also an active member of organizations including the National Association of Science Writers (NASW), the American Association for the Advancement of Science (AAAS), the American Society for Nutrition, the Institute of Food Technologists, and the National Audubon Society. David has a master's degree in human nutrition from the University of Bridgeport, and a bachelor's degree in English from University of Illinois at Springfield. He also earned his Certified Food Scientist credential from the Institute of Food Technologists.

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