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Bile

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A sample of bile.

Bile is a yellowish-green fluid produced by the liver. This solution is stored within the gallbladder before secretion into the small intestine. Bile is an integral part of digestion, especially in regards to the breakdown of lipids (fat molecules). On average, the human body produces approximately 500 – 600 ml of bile per day.[1]

Composition

Bile is a complex solution consisting of water, electrolytes, and a variety of organic compounds including: bile salts, cholesterol, phospholipids, and bilirubin (gives bile its yellowish-green hue).[1]

Function

Bile serves two functions in the body: the emulsification of fats and the secretion of waste products from the liver.[2]

The primary function of the bile is to emulsify, or break down fats and fat-soluble vitamins. Bile does not digest these lipids (fats), but merely employs bile salts to break them down into smaller droplets, which thereby increased the fats’ overall surface area. By doing this, fats can be more readily digested in the small intestine. Without the bile salts, digestion of fats and fat-soluble vitamins would be impossible.[3]

The secondary function of bile is the elimination of waste from the liver. As stated previously, the bile consists of a variety of organic compounds including cholesterol and bilirubin. These substances exist in limited amounts in the body. Therefore, the liver utilizes the bile to secrete excess compounds, such as bilirubin into the small intestine. Bilirubin will eventually be excreted through the feces. In regards to cholesterol, recent studies show that bile assists in the cholesterol metabolism. Bile helps regulate the amount of cholesterol within the liver by secreting excess cholesterol into the duodenum of the small intestine. Like bilirubin, this cholesterol is excreted through the feces.[3]

Biliary System

Bile exists in a variety of organs and ducts in the human body. These structures responsible for the creation and transportation of bile are collaboratively referred to as the biliary system.[2]

Liver

The liver consists of hexagonal-shaped tissue structures called lobules. In the center of these lobules are hepatocytes. These cells are responsible for the synthesizing of bile. Once formed, bile secretes through ducts in the lobule called bile canaliculi. The bile canaliculi travel to the six corners of the lobule. There, they transfer the bile into peripheral channels known as hepatic ducts, which form a portion of the portal triad. The hepatic ducts condense into one central channel, the common hepatic duct. [4] This channel then connects with the cystic duct, which runs the bile to the gallbladder.[5]

Gallbladder

A diagram of the gallbladder. The gallbladder stores bile before it enters the small intestine.

The gallbladder serves two purposes for bile. First, the gallbladder stores the bile until it is needed in the small intestine for digestion. Because the duct connecting the gallbladder to the small intestine (the ampulla of Vater) is closed off by a sphincter (the sphincter of Oddi), bile cannot flow freely into the small intestine. This duct only opens when specific hormones, which are triggered by eating, tell the sphincter to relax. Then, the gallbladder contracts and propels the bile into the small intestine.[1]

Second, the gallbladder concentrates the bile. While bile passes through the various channels in and around the liver, it absorbs additional water from the duct walls. However, the bile’s excess water is readily absorbed by the gallbladder. Typically, this process will concentrate bile to a solution five times more potent than it was originally.[3]

Small Intestine

Once food enters the small intestine, the hormones cholecystokinin and secretin trigger the movement of bile from the gallbladder to the duodenum (the first region of the small intestine). There, the bile can commence the breakdown of fats.[3]

And while although large portions of bile enter the small intestine each day, a relatively small percentage of the total bile is lost. In fact, it is estimated that approximately 95% of the biliary acids in the human body are reused. This occurs because the majority of these biliary acids are reabsorbed into the body’s bloodstream. This occurs predominantly in the last region of the small intestine, the ileum. The result: bile recycles itself as many as 20 times. In many cases, the same bile salts will be used 2-3 times during one digestion period.[3]

Gallstones

Gallstones form when the cholesterol in the bile outnumbers the solution's bile salts and phospholipids.

Gallstones are formed by cholesterol, an integral part of the bile composition. By nature, cholesterol is hydrophobic, meaning it does not dissolve in aqueous (water) solutions. However, bile consists predominantly of water. How does this work you ask? Well, the bile salts and phospholipids within the bile solution bind with cholesterol, thereby allowing it to be soluble in water. However, once the cholesterol outnumbers these bile salts and phospholipids, there is risk for the formation of gallstones. When this occurs, the cholesterol becomes insoluble, clumping into crystallized balls.[6]


Gallstones are both dangerous and painful. They can clog up the biliary tract, preventing the flow of bile. Without the presence of bile in the small intestine, digestion of fats and fat-soluble molecules is not possible. Gallstones also pose a threat because they can block off the flow of pancreatic juices into the small intestine.[6]

There are a variety of treatments for gallstones. Oral bile salts may be taken to help restore the cholesterol-bile salt ratio. Surgical procedures can be done to remove gallstones, or in some cases the entire gallbladder. However, if a patient cannot have surgery, shock wave therapy may be used in an attempt to shatter the gallstones into smaller, more manageable fragments.[6]

Bear Bile

Asian cultures hold moon bears captive to harvest their bile.

For thousands of years, bear bile has been harvested in Asia for medicinal purposes. According to tradition, bear bile is said to lower a person’s core temperature, which thereby alleviates fevers. However, in Asian cultures, bear bile has been prescribed for an assortment of ailments, ranging from hangovers to cancer. Patients administer bear bile in a variety of ways, including through edible powders and shower gels.[7]

This bile is extracted from Asiatic black bears, more commonly known as moon bears (named for its cream-colored crescent of fur on their chests). Historically, Asian cultures would go out and kill a moon bear for its gallbladder (which contains bile). However, beginning in the 1980s, North Korea, China, Vietnam and other Asian countries began constructing bear farms to harvest bear bile. In more recent years, many of these farms have come under fire from the animal rights community because of their cruel treatment of the bears. While some farmers merely sedate their bears for bile extraction, others keep the animals permanently caged in “crush cages”. These devices pin down the moon bears to allow for easier extraction of bile. Some farmers go as far as place permanent tubing in the moon bears’ stomachs.

It is estimated that less than 100,000 moon bears are still alive. Some reports estimate as few as 25,000. With the increase of bear farms and bear bile harvesting, the total population of Asiatic black bears continues to dwindle. In China alone, there are approximately 7,000 – 10,000 moon bears in captivity for the sole purpose of bile harvesting. And in Vietnam, although bear bile farms are now illegal, approximately 4,000 bears still remain in captivity. Because of the harsh conditions and maltreatment from their owners, bears in bile farms live usually no more than 8 years. This is in comparison to the 35 years moon bears normally live in wildlife sanctuaries. As a result of these factors, the total pollution of moon bears has decreased by 30% in the past 30 years. Asiatic black bears are now considered an endangered species.[7]

References

  1. 1.0 1.1 1.2 Shaffer, Eldon A. Overview of Biliary Function ‘’The Merck Manuel’’. Web. Last modified February 2012.
  2. 2.0 2.1 Author Unknown. The Biliary System: Anatomy and Functions. The Ohio State University Wexner Medical Center. Web. Accessed 24 April 2013.
  3. 3.0 3.1 3.2 3.3 3.4 Bowen, R. Secretion of Bile and the Role of Bile Acids In Digestion ‘’Colorado State. Web. 23 November 2001.
  4. Wile, Jay L., and Shannon, Marilyn M. The Human Body: Fearfully and Wonderfully Made!. Cincinnati: Apologia Educational Ministries, Inc., 2001. Pg.403. Print.
  5. Wile, Jay L., and Shannon, Marilyn M. The Human Body: Fearfully and Wonderfully Made!. Cincinnati: Apologia Educational Ministries, Inc., 2001. Pg.404. Print.
  6. 6.0 6.1 6.2 Author Unknown. Regulation of Bile Release ‘’The University of Washington’’. Web. Accessed 8 May 2013.
  7. 7.0 7.1 MacGregor, Fiona. Inside a bear bile farm in Laos The Telegraph. Web. 19 August 2010.