Difference between revisions of "Bile" - New World Encyclopedia
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| − | '''Bile''' (or ''gall'') is a | + | '''Bile''' (or ''gall'') is a thick, greenish-yellow [[alkali]]ne fluid. It assists in digestion by breaking down fats, mostly triglycerides (primary form of lipid in animals and plants as well as the main source of fat calories in the Western diet), into monoglycerides and two free [[fatty acids]]. In most vertebraes, bile is made in the [[liver]] and stored in the [[gallbladder]] between meals. When fats are present in the digestive tract after the consumption of a meal, a signal from cholecystokinin, or CCK (hormone released from the small intestine) stimulates the [[gallbladder]] to contraction and release bile. The bile is discharged into the duodenum (first part of the small intestine where most of digestion occurs), where it consequently aids the process of fat [[digestion]]. |
| − | + | The components of bile are: | |
* Water | * Water | ||
* Cholesterol | * Cholesterol | ||
* Lecithin (a [[phospholipid]]) | * Lecithin (a [[phospholipid]]) | ||
| − | * Bile pigments ( | + | * Bile pigments (bilirubin & biliverdin) |
| − | * Bile salts (sodium glycocholate & sodium taurocholate) | + | * Bile salts and bile acids (sodium glycocholate & sodium taurocholate) |
| + | * Small amounts of copper and other excreted metals | ||
==Physiology== | ==Physiology== | ||
| − | Bile [[ | + | Bile salts are bile acids conjugated with [[amino acids]]. Bile acids are steroid compounds ([[deoxycholic acid|deoxycholic]] and [[cholic acid|cholic]] acid), often combined with [[glycine]] and [[taurine]]. The most important compounds are the salts of [[taurocholic acid]] and [[deoxycholic acid]]. Bile acids act as detergents, helping to emulsification|emulsify [[fats]] by increasing the surface area of the fats to help enzyme action; thus bile acids and salts aid in the absorption of fats in the small intestine. |
| − | Bile salts | + | Bile salts function by combining with [[phospholipids]] to break down large fat globules in a process known as emulsification. Bile salts associate their hydrophobic side with lipids and their hydrophilic side with water. These emulsified droplets are then organized into many micelles (small droplets of phospholipid arranged so that the interior is filled with hydrophobic fatty acid tails), which increases overall absorption by helping make fat globules into smaller particles. |
| + | |||
| + | Aside from its digestive function, bile serves as the route for excretion of the [[hemoglobin]] breakdown product bilirubin (gives bile its yellowish color). Bile, which also contains [[cholesterol]], occasionally aggregates into lumps in the [[gallbladder]], resulting in the formation of [[Cholelithiasis|gallstones]]. | ||
In species with a gall bladder (humans and most domestic animals except [[horse]]s and [[rat]]s), further modification of bile occurs in that organ. The gall bladder stores and concentrates bile during the fasting state. Typically, bile is concentrated five-fold in the gall bladder by absorption of water and small electrolytes - virtually all of the organic molecules are retained. | In species with a gall bladder (humans and most domestic animals except [[horse]]s and [[rat]]s), further modification of bile occurs in that organ. The gall bladder stores and concentrates bile during the fasting state. Typically, bile is concentrated five-fold in the gall bladder by absorption of water and small electrolytes - virtually all of the organic molecules are retained. | ||
Revision as of 02:58, 18 May 2006
Bile (or gall) is a thick, greenish-yellow alkaline fluid. It assists in digestion by breaking down fats, mostly triglycerides (primary form of lipid in animals and plants as well as the main source of fat calories in the Western diet), into monoglycerides and two free fatty acids. In most vertebraes, bile is made in the liver and stored in the gallbladder between meals. When fats are present in the digestive tract after the consumption of a meal, a signal from cholecystokinin, or CCK (hormone released from the small intestine) stimulates the gallbladder to contraction and release bile. The bile is discharged into the duodenum (first part of the small intestine where most of digestion occurs), where it consequently aids the process of fat digestion.
The components of bile are:
- Water
- Cholesterol
- Lecithin (a phospholipid)
- Bile pigments (bilirubin & biliverdin)
- Bile salts and bile acids (sodium glycocholate & sodium taurocholate)
- Small amounts of copper and other excreted metals
Physiology
Bile salts are bile acids conjugated with amino acids. Bile acids are steroid compounds (deoxycholic and cholic acid), often combined with glycine and taurine. The most important compounds are the salts of taurocholic acid and deoxycholic acid. Bile acids act as detergents, helping to emulsification|emulsify fats by increasing the surface area of the fats to help enzyme action; thus bile acids and salts aid in the absorption of fats in the small intestine.
Bile salts function by combining with phospholipids to break down large fat globules in a process known as emulsification. Bile salts associate their hydrophobic side with lipids and their hydrophilic side with water. These emulsified droplets are then organized into many micelles (small droplets of phospholipid arranged so that the interior is filled with hydrophobic fatty acid tails), which increases overall absorption by helping make fat globules into smaller particles.
Aside from its digestive function, bile serves as the route for excretion of the hemoglobin breakdown product bilirubin (gives bile its yellowish color). Bile, which also contains cholesterol, occasionally aggregates into lumps in the gallbladder, resulting in the formation of gallstones.
In species with a gall bladder (humans and most domestic animals except horses and rats), further modification of bile occurs in that organ. The gall bladder stores and concentrates bile during the fasting state. Typically, bile is concentrated five-fold in the gall bladder by absorption of water and small electrolytes - virtually all of the organic molecules are retained.
The human liver produces about a quart (or litre) of bile per day. 95% of secreted bile salts are reabsorbed in the terminal ileum and re-used. Since bile increases the absorption of fats, it is an important part of the absorption of the fat-soluble vitamins: A, D, E, and K.
Bile from slaughtered animals can be mixed with soap. This mixture, applied to textiles a few hours before washing, is a traditional and rather effective method for removing various kinds of tough stains.
Four humours
Yellow bile and black bile were two of the four vital fluids or humours of ancient and medieval medicine; for example, melancholia was believed to be caused by a bodily surplus of black bile. (The other two were phlegm and blood.)
Yellow bile is sometimes called ichor.
See also
- Intestinal juice
- Bile acid sequestrant
- Bilirubin
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