- Related Topics:
- bile acid
- bile salt
- ursodeoxycholic acid
- lithocholic acid
- cholic acid
- On the Web:
- National Center for Biotechnology Information - Physiology, Bile (Oct. 27, 2026)
bile
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What is bile?
Bile is a greenish-yellow secretion produced in the liver, then passed to the gallbladder for concentration and storage. It assists in the digestion of fats in the small intestine. Bile consists of bile acids and salts, phospholipids, cholesterol, pigments, water, and electrolyte chemicals.
Bile acids act as detergents, which emulsify dietary fats into small droplets that digestive enzymes readily break down. They also help absorb fat-soluble vitamins by forming micelles, which transport vitamins and lipids across the intestinal lining. Bile acids also eliminate excess cholesterol from the body and affect metabolic and immune functions.
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Where is bile produced in the body?
Bile is produced in the liver, a vital secretion that aids in the digestion of fats in the duodenum. After production, bile is transported to the gallbladder for concentration and storage. The liver cells continually secrete bile into the common bile duct and gallbladder.
The amount of bile secreted into the duodenum is controlled by hormones and the vagus nerve. Bile consists of bile acids and salts, phospholipids, cholesterol, pigments, water, and electrolyte chemicals, maintaining a slightly alkaline solution.
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What are the main components of bile?
Bile, a secretion produced in the liver, aids in fat digestion in the small intestine. It consists of bile acids and salts, which emulsify fats, and phospholipids, mainly lecithin, that help in the absorption of fats.
Cholesterol, a sterol absorbed from diet or synthesized by the liver and intestinal lining, is another key component. Bile also contains bilirubin, a pigment from hemoglobin breakdown, and electrolytes that maintain a slightly alkaline pH. The liver removes water-insoluble wastes like steroids and drugs, carrying them in bile fluid to the excretory system.
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How does bile help with digestion?
Bile, produced in the liver, is essential for digestion. After production, bile is passed to the gallbladder for concentration, storage, or transport to the duodenum (the first section of the small intestine).
Bile's primary digestive function is to aid in the digestion and dispersion of fats within the small intestine. Bile salts act as detergents to emulsify dietary fats into smaller droplets, which reduces surface tension and prepares them for the action of fat-splitting enzymes. Bile acids also help the body absorb fat-soluble vitamins (A, D, E, and K) by forming micelles that transport lipids and vitamins across the intestinal lining.
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What is the role of bile acids in breaking down fats?
Bile acids, synthesized in the liver from cholesterol, are essential for the digestion and absorption of fats and fat-soluble vitamins. They act as detergents, emulsifying dietary fats into small droplets that digestive enzymes can readily break down.
These acids also form micelles, which are critical for transporting vitamins and lipids across the intestinal lining, aiding in the absorption of fat-soluble vitamins A, D, E, and K. After their emulsifying actions, bile acids are reabsorbed in the small intestine and reused, a process called enterohepatic circulation. This efficient cycle handles a significant amount of bile acids daily, highlighting their importance in maintaining metabolic and immune functions.
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How does the body recycle or get rid of bile after it is used?
Bile, produced in the liver and stored in the gallbladder, aids in fat digestion. After bile emulsifies fats in the small intestine, the bile acids are reabsorbed in the lower small intestine and transported back to the liver via the bloodstream to be reused. This process is called enterohepatic circulation.
A small fraction of bile acids escapes this cycle and is lost in feces, which is the primary way the body excretes cholesterol. The liver synthesizes new bile acids from cholesterol to replace those lost, maintaining the necessary supply for digestion.
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bile, greenish yellow secretion that is produced in the liver and passed to the gallbladder for concentration, storage, or transport into the first region of the small intestine, the duodenum. Its function is to aid in the digestion of fats in the duodenum. Bile is composed of bile acids and salts, phospholipids, cholesterol, pigments, water, and electrolyte chemicals that keep the total solution slightly alkaline (with a pH of about 7 to 8). Bile is continually secreted from the cells of the liver into the common bile duct and gallbladder; once in the gallbladder it is usually concentrated to about 5 times—and sometimes as high as 18 times—the strength of the original secretion. The amount of bile secreted into the duodenum is controlled by the hormones cholecystokinin, secretin, gastrin, and somatostatin and also by the vagus nerve. About 800 to 1,000 ml of bile (before concentration) are produced daily by the liver.
Bile salts are composed of the salts of four different kinds of free bile acids (cholic, deoxycholic, chenodeoxycholic, and lithocholic acids); each of these acids may in turn combine with glycine or taurine to form more complex acids and salts. Bile salts and acids can be synthesized from cholesterol or extracted from the bloodstream by the liver. They pass from the liver into the small intestine, where they act as detergents to emulsify fat and reduce the surface tension on fat droplets to prepare them for the action of pancreatic and intestinal fat-splitting enzymes. The salts are large, negatively charged ions that are not readily absorbed by the upper region of the small intestine; consequently, they remain in the small intestine until most of the fat is digested. In the lower small intestine, the salts and acids are absorbed and passed back into the bloodstream until they are once again extracted by the liver; this cycle, from the liver to the small intestine and blood and then back to the liver, is called enterohepatic circulation. Some salts and acids are lost during this process; these are replaced in the liver by continual synthesis from cholesterol. The rate of synthesis is directly related to the amount of acids and salts lost. Bile salts do not normally reach the colon; when they do, however, they may inhibit the absorption of water and sodium, causing a watery diarrhea.
Bile salts and acids are transported in a fluid that contains water, sodium, chloride, and bicarbonates. This fluid is produced in the liver, and it serves to neutralize hydrochloric acid passed from the stomach into the small intestine. Water-insoluble wastes that the liver removes from blood, such as cholesterol, steroids, drugs, and hemoglobin pigments, are carried in the fluid to the excretory system. Hemoglobin pigments are broken down, producing several bile fluid compounds, including bilirubin, which has no known function other than that of a colouring agent. Traces of other substances can also be found in bile including mucus, serum proteins, lecithin, neutral fats, fatty acids, and urea.
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