Bile
Bile is a yellow or green fluid produced by the liver, primarily by hepatocytes, and plays a crucial role in digestion, particularly in the breakdown of fats. Composed of water, cholesterol, bilirubin (a pigment from red blood cell breakdown), bile acids, lecithin, and bicarbonate, bile is synthesized in the liver and stored in the gallbladder, a small organ adjacent to the liver. The liver can produce nearly one liter of bile per day, which is transported through small channels called canaliculi before entering the common bile duct and gallbladder.
When food is consumed, the gallbladder releases bile into the small intestine, specifically the duodenum, to aid in the emulsification of dietary fats. The release of bile is regulated by the sphincter of Oddi, which opens in response to the presence of food. However, bile can be associated with certain health issues, the most notable being gallstones, which can form when cholesterol in bile crystallizes. These stones can obstruct bile ducts and potentially lead to severe health complications such as liver failure. Risk factors for gallstone formation include genetics, obesity, aging, pregnancy, diabetes, and rapid weight loss.
Subject Terms
Bile
Biology
Also known as: Gall
Anatomy or system affected: Blood vessels, gallbladder, immune system, liver, muscles
Definition: Bile has an important role in digestion, but it is not an enzyme; that is, on its own, it does not break down molecules. Bile is an emulsifier, increasing the surface area of fat globules to provide a greater area on which lipase, an enzyme that digests fat, can act. Bile, by acting as an emulsifier, also has a role in the absorption of fat-soluble vitamins such as vitamins A, D, E, and K.
Structure and Function
Bile is a yellow or green fluid that is secreted by hepatocytes or liver cells. Bile is composed of several materials, including water, cholesterol, pigments (bilirubin, produced by the breakdown of red blood cells), acid, lecithin, and bicarbonate. Bile is produced in the liver, but it is stored in the gallbladder, a small saclike organ that is tucked into the liver. The human liver is able to produce almost one liter of bile a day.
The bile produced by the hepatocytes moves along canaliculi, small passageways in the liver. The canaliculi join at the common hepatic duct, which then meets with the cystic duct of the gallbladder and forms the common bile duct; bile then empties into the gallbladder. The gallbladder concentrates the bile by removing some of the water. After a meal is eaten, the gallbladder discharges bile by way of the pancreatic duct into the small intestine (specifically, the duodenum) to assist in the digestion of lipids (fats). Like many structures in the digestive system, a sphincter, in this case, called the sphincter of Oddi, controls the passage of materials. Before meals, the sphincter is closed so that bile flows from the liver to the gallbladder for storage. When food is sensed in the small intestine, the sphincter opens and releases bile.
Disorders and Diseases
The most common problem associated with bile is the formation of gallstones, which occur when the cholesterol in the bile forms lumps or stones. Gallstones can block bile ducts, which can lead to liver failure. The risk factors for the formation of gallstones include genetics, obesity, aging, pregnancy, diabetes, liver disease, and rapid weight loss as a result of “crash dieting” or gastric bypass surgery. Gallstones take many years to form, so it is often difficult to pinpoint their exact cause. They range in size from sand-like crystals to large pebbles.
Bibliography
“Bile Reflux: Symptoms, Treatment, Causes & What It Is.” Cleveland Clinic, 18 Nov. 2021, my.clevelandclinic.org/health/diseases/22056-bile-reflux. Accessed 22 July 2023.
Choi, Young, and William B. Silverman. "Biliary Tract Disorders, Gallbladder Disorders, and Gallstone Pancreatitis." American College of Gastroenterology, July 2013.
Chwistek, Marcin. "Conditions InDepth: Gallstones." Health Library, October 11, 2012.
Feldman, Mark, Lawrence S. Friedman, and Lawrence J. Brandt, eds. Sleisenger and Fordtran’s Gastrointestinal and Liver Disease: Pathophysiology, Diagnosis, Management. 9th ed. Philadelphia: Saunders/Elsevier, 2010.
Johnson, Leonard R., ed. Gastrointestinal Physiology. 7th ed. Philadelphia: Mosby/Elsevier, 2007.
Scanlon, Valerie, and Tina Sanders. Essentials of Anatomy and Physiology. 6th ed. Philadelphia: F. A. Davis, 2011.