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22.7F: Bile

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    8049
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    Bile is a fluid produced by the liver that aids the process of digestion and the absorption of lipids in the small intestine.

     

    LEARNING OBJECTIVES

     

    Summarize the composition and function of bile

     

    KEY TAKEAWAYS

    Key Points

     

    • Bile is a composition of the following materials: water (85%), bile salts (10%), mucus and pigments (3%), fats (1%), inorganic salts (0.7%), and cholesterol (0.3%).
    • Bile can either drain directly into the duodenum or be temporarily stored in the gallbladder.
    • Bile, which is alkaline, also has the function of neutralizing any excess stomach acid in the small intestine.

     

    Key Terms

     

    • bile: A bitter, brownish-yellow or greenish-yellow secretion produced by the liver, stored in the gallbladder, and discharged into the duodenum, where it aids the process of digestion.

    This is a micrograph image of bile (seen as yellow material) in a liver biopsy.

     

    Bile: Micrograph of bile (yellow material) in a liver biopsy.

    Bile, or gall, is a bitter-tasting, dark-green to yellowish-brown fluid produced by the liver that aids the process of digestion of lipids in the small intestine. Bile is stored in the gallbladder, and upon eating is discharged into the duodenum through the bile duct. Bile is a composition of the following materials: water (85%), bile salts (10%), mucus and pigments (3%), fats (1%), inorganic salts (0.7%), and cholesterol (0.3%).

    Bile acts as a surfactant, helping to emulsify the fats in the food, in the same way that soap emulsifies fat. The bile salts are ionically charged, with a hydrophobic end and a hydrophillic end.

    When exposed to water mixed with fat, such as in the small intestine, the bile salts congregate around a fat droplet with their hydrophobic side pointing towards the fat and their hydrophillic side pointing towards the water. This increases the surface area of the fat and allows greater access by the pancreatic enzymes that break down fats.

    Since bile increases the absorption of fats, it is an important part of the absorption of the fat-soluble vitamins, such as the vitamins D, E, K, and A.

    Besides its digestive function, bile serves also as the route of excretion for bilirubin, a waste byproduct of red blood cells that is recycled by the liver. The alkaline bile also has the function of neutralizing any excess stomach acid before it enters the ileum, the final section of the small intestine.

    Bile salts also act as bactericides, destroying many of the microbes that may be present in the food.

    This is a drawing of bile salt action on lipids. The image shows a circle labeled lipid surrounded by bile salts.

     

    Bile salt action on lipids: Bile salts congregate around fat and separate them into small droplets called micelles.

     

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