Without bile, lipids cannot be digested. What is the function of bile acids and what is their structure? conjugated bile acids

Over the past few decades, a lot of new information about bile and its acids has been obtained. In this regard, it became necessary to revise and expand ideas about their significance for the life of the human body.

The role of bile acids. General information

The rapid development and improvement of research methods has made it possible to study bile acids in more detail. For example, now there is a clearer understanding of metabolism, their interaction with proteins, lipids, pigments and their content in tissues and fluids. Confirmed information indicates that bile acids are of great importance not only for the normal functioning of the gastrointestinal tract. These compounds are involved in many processes in the body. It is also important that, thanks to the use of the latest research methods, it was possible to most accurately determine how bile acids behave in the blood, as well as how they affect respiratory system. Among other things, the compounds affect some parts of the central nervous system. Their importance in intracellular and external membrane processes has been proven. This is due to the fact that bile acids act as surfactants in the internal environment of the body.

Historical facts

This type of chemical compounds was discovered by the scientist Strecker in the middle of the 19th century. He managed to find out that bile has two. The first of them contains sulfur. The second also contains this substance, but has a completely different formula. In the process of splitting these chemical compounds, cholic acid is formed. As a result of the transformation of the first compound mentioned above, glycerol is formed. At the same time, another bile acid forms a completely different substance. It's called taurine. As a result, the original two compounds were given names with the same names as the produced substances. This is how tauro- and glycocholic acid appeared, respectively. This discovery of the scientist gave a new impetus to the study of this class of chemical compounds.

Bile acid sequestrants

These substances are a group of drugs that have a hypolipidemic effect on the human body. AT last years they have been actively used to lower blood cholesterol levels. This made it possible to significantly reduce the risk of various cardiovascular pathologies and coronary disease. At the moment in modern medicine widely used by another group more effective drugs. These are statins. They are used much more often due to the smaller number side effects. At the present time, bile acid sequestrants are used less and less. Sometimes they are used exclusively in the framework of complex and auxiliary treatment.

Detailed information

The steroid class includes monocarbaic hydroxy acids. They are active and poorly soluble in water. These acids result from the processing of cholesterol by the liver. In mammals, they consist of 24 carbon atoms. The composition of the dominant bile compounds in different types animals is different. These types form taucholic and glycolic acids in the body. Chenodeoxycholic and cholic compounds belong to the class of primary compounds. How are they formed? In this process, liver biochemistry matters. Primary compounds arise from the synthesis of cholesterol. Next, the conjugation process takes place together with taurine or glycine. These types of acids are then secreted into the bile. Lithocholic and deoxycholic substances are part of the secondary compounds. They are formed in the large intestine from primary acids under the influence of local bacteria. The rate of absorption of deoxycholic compounds is much higher than that of lithocholic compounds. Other secondary bile acids occur in very small amounts. For example, ursodeoxycholic acid is one of them. If chronic cholestasis occurs, then these compounds are present in large quantities. The normal ratio of these substances is 3:1. While with cholestasis, the content of bile acids is considerably exceeded. Micelles are aggregates of their molecules. They are formed only when the concentration of these compounds in an aqueous solution exceeds the limit mark. This is due to the fact that bile acids are surfactants.

Features of cholesterol

This substance is poorly soluble in water. The rate of solubility of cholesterol in bile depends on the ratio of lipid concentration, as well as the molar concentration of lecithin and acids. Mixed micelles arise only when the normal proportion of all these elements is maintained. They contain cholesterol. The precipitation of its crystals is carried out under the condition of violation of this ratio. acids are not limited to removing cholesterol from the body. They promote the absorption of fats in the intestines. Micelles are also formed during this process.

Connection traffic

One of the main conditions for the formation of bile is the active movement of acids. These compounds play an important role in the transport of electrolytes and water in the small and large intestines. They are solid powders. Their melting point is quite high. They have a bitter taste. Bile acids are poorly soluble in water, while they are good in alkaline and alcoholic solutions. These compounds are derivatives of cholanic acid. All such acids occur exclusively in cholesterol hepatocytes.

Influence

The most important among all acidic compounds are salts. This is due to a number of properties of these products. For example, they are more polar than free bile salts, have a small micelle concentration limit, and are secreted faster. The liver is the only organ capable of converting cholesterol into specific cholanic acids. This is due to the fact that the enzymes that take part in conjugation are contained in hepatocytes. The change in their activity is directly dependent on the composition and rate of fluctuations of the bile acids of the liver. The process of synthesis is regulated by the mechanism. This means that the intensity of this phenomenon is in proportion to the current of secondary bile acids in the liver. The rate of their synthesis in the human body is quite low - from two hundred to three hundred milligrams per day.

Main goals

Bile acids have a wide range of uses. In the human body, they mainly carry out the synthesis of cholesterol and affect the absorption of fats from the intestines. In addition, the compounds are involved in the regulation of bile secretion and bile formation. These substances also have a strong influence on the process of digestion and absorption of lipids. Their compounds are collected in the small intestine. The process occurs under the influence of monoglycerides and free fatty acids that are on the surface of fat deposits. In this case, a thin film is formed, which prevents the connection of small drops of fat into larger ones. Due to this, a strong decrease occurs. This leads to the formation of micellar solutions. They, in turn, facilitate the action of pancreatic lipase. With the help of a fatty reaction, it breaks them down into glycerol, which is then absorbed by the intestinal wall. Bile acids combine with fatty acids that do not dissolve in water and form choleic acids. These compounds are easily broken down and quickly absorbed by the villi of the upper part. small intestine. Choleic acids are converted into micelles. Then they are absorbed into the cells, while easily overcoming their membranes.

The latest research information in this area has been obtained. They prove that the relationship between fatty and bile acids in the cell breaks down. The former are the end result of lipid absorption. The latter - through the portal vein penetrate the liver and blood.

Human bile acids

The main types of bile acids found in the human body are the so-called primary bile acids (primarily secreted by the liver): cholic acid (3α, 7α, 12α-trioxy-5β-cholanic acid) and chenodeoxycholic acid (3α, 7α-dioxy-5β- cholanic acid), as well as secondary ones (formed from primary bile acids in the colon under the action of intestinal microflora): deoxycholic acid (3α, 12α-dioxy-5β-cholanic acid), lithocholic and ursodeoxycholic acid. Of the secondary in the enterohepatic circulation, only deoxycholic acid, which is absorbed into the blood and then secreted by the liver in the bile, participates in an amount that affects the physiology.

Allocholic, ursodeoxycholic and lithocholic acids are stereoisomers of cholic and deoxycholic acids.

All human bile acids have 24 carbon atoms in their molecules.

Animal bile acids

Most bile acids have 24 carbon atoms in their molecules. However, there are bile acids, the molecules of which have 27 or 28 carbon atoms. The structure of the dominant bile acids in various kinds animals is different. In the bile acids of mammals, the presence of 24 carbon atoms in the molecule is characteristic, in some amphibians - 27 atoms.

Cholic acid is found in the bile of goats and antelopes (and humans), β-fococholic acid - in seals and walruses, nutricholic acid - in beaver, allocholic acid - in leopard, bitocholic acid - in snakes, α-muricholic and β-muricholic acid - in rats, giocholic and β-hyodeoxycholic - in a pig, α-hyodeoxycholic - in a pig and a wild boar, deoxycholic - in a bull, deer, dog, sheep, goat and rabbit (and human), chenodeoxycholic - in a goose, bull, deer, dog, sheep, goat and rabbit (and human), buffodeoxycholic - in toads, α-lagodeoxycholic - in rabbits, lithocholic - in rabbits and bulls (and humans).

Bile duodenogastric reflux

Reflux gastritis

Reflux gastritis by modern classification refers to chronic type C gastritis. One of the causes that cause it is the entry of components of the contents of the duodenum, including bile acids, into the stomach during duodenogastric reflux. Prolonged exposure to bile acids, lysolecithin, pancreatic juice on the gastric mucosa causes dystrophic and necrobiotic changes in the surface epithelium of the stomach.

As a drug that reduces the pathological effect of bile acids in duodenogastric reflux, ursodeoxycholic acid is used, which, when bile acids are reabsorbed in the intestine, changes the pool of bile acids involved in the enterohepatic circulation from more hydrophobic and potentially toxic to less toxic, more soluble in water and to a lesser extent irritate the gastric mucosa.

Duodenogastric esophageal reflux

Bile acids enter the mucosa of the esophagus due to duodenal gastric and gastroesophageal reflux, collectively called duodenogastric esophageal. Conjugated bile acids, and, first of all, conjugates with taurine, have a more significant damaging effect on the esophageal mucosa at an acidic pH in the esophageal cavity. Unconjugated bile acids, present in the upper digestive tract, mainly in ionized forms, penetrate the mucosa of the esophagus more easily and, as a result, are more toxic at neutral and slightly alkaline pH. Thus, refluxes throwing bile acids into the esophagus can be acidic, non-acidic and even alkaline, and therefore pH monitoring of the esophagus is not always enough to detect all bile refluxes, non-acidic and alkaline bile refluxes require impedance-pH-metry of the esophagus for their determination.

Bile acids - drugs

Two bile acids - mentioned in the section "Reflux gastritis" ursodeoxycholic and chenodeoxycholic are internationally recognized medicines and are assigned by the anatomical-therapeutic-chemical classification to section A05A Preparations for the treatment of diseases of the gallbladder.

pharmachologic effect of these drugs is based on the fact that they change the composition of the pool of bile acids in the body (for example, chenodeoxycholic acid increases the concentration of glycocholic acid compared to taurocholic acid), thereby reducing the content of potentially toxic compounds. In addition, both drugs contribute to the dissolution of cholesterol gallstones, reduce the amount of cholesterol, quantitatively and qualitatively change the composition of bile.

see also

Notes

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See what "Bile acids" are in other dictionaries:

BILE ACIDS, a group of steroid acids found in the BILE. In humans, the most common is cholic acid, C24H40O5, whose carboxyl group is linked to the amino group of glycine and taurine (amino acids). Bile acids serve... Scientific and technical encyclopedic dictionary

Tetracycline. monocarboxylic hydroxy acids from the class of steroids, produced by the liver of vertebrates from cholesterol and secreted with bile into duodenum. In different groups of animals, the set of fatty acids varies and is associated with the nature of the food. Main AND.… …

bile acids- - compounds of a steroid nature, acting as lipid emulsifiers and activators of lipolytic enzymes ... Concise Dictionary of Biochemical Terms

bile acids- tulžies rūgštys statusas T sritis chemija apibrėžtis Steroidinės hidroksirūgštys, cholio rūgšties dariniai. atitikmenys: engl. bile acids rus. bile acids... Chemijos terminų aiskinamasis žodynas

- (acida cholica) organic acids that are part of bile and are hydroxylated derivatives of cholanic acid; play an important role in the digestion and absorption of lipids, are the end product of cholesterol metabolism ... Big Medical Dictionary

Monocarboxylic hydroxy acids belonging to the class of steroids. Almost all Zh. to. derivatives of nature. cholanic to you (f la Ia). Naib. common are its mono, di and trihydroxy-substituted containing 24 C atoms; also known are di, three and ... ... Chemical Encyclopedia

Tetracycline polyols from the class of steroids containing 27 carbon atoms and at least one OH group at the end of the side chain. They are produced by the liver of fish and amphibians from cholesterol and perform the same role in their digestion as bile ... ... Biological encyclopedic dictionary

Organic acids present in bile; more common in the form of bile salts (sodium glycocholate and sodium taurocholate). These include: cholic, deoxycholic, glycocholic and taurocholic acids.

The fact is that the cyclic structure of cholesterol cannot be opened and split into small compounds for their subsequent excretion. Only liver cells convert cholesterol into bile acids, which are used as emulsifiers for lipid digestion.

In the human body, the metabolic pathways of synthesized bile acids are very peculiar. Knowing them allows you to understand the mechanisms of development and symptoms of a number of diseases. The so-called primary bile acids are synthesized in the liver: cholic and chenodeoxycholic.

The side chain carboxyl group of these acids can form amide bonds with either glycine or taurine. As a result, conjugated bile acids. This determines their emulsifying properties, since p To side chain ionic group is lower than that of the parent carboxyl group. If cholic acid acts as the initial bile acid, its conjugated forms are glycocholic and taurocholic acids.

The formed bile acids come from the liver to the duodenum with bile. In the neutral or slightly alkaline environment of the intestinal lumen, bile acids, mainly taurocholic and glycocholic, are amphiphilic and serve not only as emulsifying agents, but also as stabilizers of the resulting emulsion. By interacting with the hydrophobic parts of their molecules with fat, and the hydrophilic, polar part with the aqueous contents of the intestine, bile acids contribute to the crushing of fat into small particles, that is, emulsification. The stabilizing effect of fatty acids on the resulting emulsion particles is due to the fact that they prevent the conglomeration (sticking) of the emulsion particles. Bile acids cover the surface of the emulsion particle in the form of a monolayer (Fig. 6.9). At the same time, the polar

Table 6.3. Composition of human bile

* - if the level exceeds 15 mol%, gallstones may form

parts of bile acid molecules. As a result, the surface of the particle acquires a total electric charge, which will be the same for all other emulsion particles. Due to the electrostatic interaction between the individual particles, repulsion occurs.

Fig.6.9. Formation of a bile acid shell around an emulsion or micellar particle during lipid digestion

In the intestine, under the action of bacterial enzymes, secondary bile acids are formed, which catalyze the cleavage of the 7-OH group and the conjugated amino acid. As a result, deoxycholic and lithocholic acids are formed from two primary bile acids.

Recirculation of bile acids between the liver and intestines. To summarize, it turns out that 15–30 g of bile acids are secreted from the liver per day, and only 0.5 g of them are excreted with feces. The remaining bile acids are absorbed from small intestine, i.e., during digestion, bile acids are released into the lumen of the small intestine, its upper sections, and then in the lower part of the small intestine, they are reabsorbed into the portal vein system. This process of secretion and reabsorption is known as the hepato-intestinal circulation (Figure 6.10).

Fig.6.10. Hepato-intestinal bile acid recirculation

Bile acids tetracyclic monocarboxylic hydroxy acids from the class of steroids. By chemical nature, they are derivatives of cholanic acid. They are the main end product of cholesterol metabolism. Bile acids are formed in the liver and excreted in the bile, both in free form and as paired compounds (paired or conjugated bile acids) with glycine and taurine. Glycine and taurine are linked to bile acids by peptide bonds. Human bile mainly contains cholic, deoxycholic and chenodeoxycholic. In addition, lithocholic, allocholic and ureodeoxycholic acids are present in small amounts. In hepatocytes, chenodeoxycholic and cholic acids are directly synthesized from cholesterol - primary bile acids?. After the release of bile into the intestine, under the action of enzymes of the intestinal microflora, lithocholic and deoxycholic acids are formed from the primary bile acids, secondary bile acids. They are absorbed from the intestines, with the blood of the portal vein enter the liver, and then into the bile. It should be noted that intestinal microorganisms form about 20 different secondary bile acids, but only deoxycholic and, to a lesser extent, lithocholic acids are absorbed in noticeable amounts; the rest are excreted from the body.
Due to the presence of α-hydroxyl groups in the structure, bile acids and their salts are amphiphilic compounds and have detergent properties. The main functions of acids are the formation of micelles, emulsification of fats and solubilization of lipids in the intestine, which increases the efficiency of pancreatic lipase and promotes lipid absorption. Bile acids are also involved in the regulation of cholesterol synthesis, minimizing the buildup or deficiency of cholesterol in the body, and the regulation of bile production and secretion. Their pronounced influence on the functional state of various departments was found. nervous system. It has been determined that they act as surfactants of the internal environment of the body: they do not pass through the membranes, but regulate the membrane processes of cells and intracellular structures.

In violation of bile formation or bile secretion (for example, due to blockage of the bile duct gallstone) the conditions for the digestion of fats and the absorption of hydrolysis products deteriorate, and a significant part of them is excreted from the body. Fat-soluble vitamins are also not absorbed, which leads to the development of hypovitaminosis.
A blood test is indicated for patients with impaired excretory function of the liver. An increase in the amount of bile acids is possible even with mild deviations. The level increases with cholestasis (primarily with a long course), which develops against the background of primary biliary cirrhosis. Another reason for the increase in titer is insufficient bile secretion during treatment with pharmaceuticals, tests also allow you to confirm or exclude:

• subhepatic jaundice,
• alcoholic liver disease
• hepatitis-like syndrome in infants,
• viral or toxic hepatitis,
• cystic fibrosis,
• congenital infection bile ducts,
• acute cholecystitis.

The main component of bile are organic acids. These compounds provide a mixture of food fats with digestive juice, in which lipase is activated by the pancreas. This enzyme is necessary for the breakdown of fats, which in the form of tiny droplets after hydrolysis are absorbed by the cells of the small intestine mucosa. There they are further processed with the withdrawal of harmful cholesterol. And this is just one role of bile among many.

What are the components of acid in bile?

Bile acids are also called cholic, cholic or cholenic derivatives of C23H39COOH. Organic acid compounds are part of bile and are residual products of cholesterol metabolism. Holens perform important functions:

• digestion of fats with their subsequent absorption;
• supporting the growth and functioning of stable microflora in the intestine.

In addition to cholic acid compounds, the liquid contains chenodeoxycholic and deoxycholic acids. The normal proportion of cholic, chenodeoxycholic and deoxycholic substances to bile is 1:1:0.6, respectively.

If bile acids are present in the urine, liver function should be checked. Normally, their number should not exceed 0.5 g or they should be absent.

Functions of bile acids

Bile is endowed with amphiphilic properties. The connection has two parts:

• in the form of a side chain of glycine or taurine, which are endowed with a hydrophilic quality;
• cyclic section of the molecule - hydrophobic.

The amphiphilicity of acidic compounds endows them with active surface properties that allow them to participate in the digestion, emulsification and absorption of fats. The compound molecule unfolds so that its hydrophobic arms are immersed in the fat and the hydrophilic ring is immersed in the water phase.

This allows a stable emulsion to be obtained. Thanks to the active surface, which reliably adheres to both phases during emulsification, the process of crushing one drop of fat into 106 tiny particles is improved. In this form, fats are digested and absorbed faster. Due to the properties of bile fluid:

• activates lipolytic enzymes with the conversion of prolipase to lipase, which increases pancreatic properties several times;
• regulates and improves intestinal motility;
• has bactericidal effects, which allows timely suppression of putrefactive processes;
• promotes the dissolution of lipid hydrolysis products, which improves their absorption and transformation into ready-made substances for metabolism.

Bile acids are synthesized in the liver. Compounds are formed in a cycle: after reacting with fats, most of them go back to the liver to produce a new portion of fluid. The body daily removes acid in the amount of 0.5 g of its entire circulating mass, so 90% of the mass goes back to the starting point of synthesis. Complete renewal of bile occurs in 10 days.

If the processes of bile formation are disturbed, which can occur due to blockage of the bile duct by a stone, fats are not digested properly, do not enter in full into circulatory system. Therefore, fat-soluble vitamins are not absorbed, as a result, a person earns hypovitaminosis.

Primary and secondary acids

With the help of cholesterol hepatocytes, primary bile acids are produced, represented by a group of chenodeoxycholic and cholic compounds. Under the influence of enzymes present in the intestinal microflora, the primary ones are converted into secondary bile acids, represented by lithocholic and deoxycholic groups.

The resulting acidic substances are emulsified with fats and absorbed into the portal vein, through which they enter the liver tissues and the gallbladder. Microorganisms in the intestine are capable of forming over 20 types of secondary acids, but all of them, except for deoxycholic and lithocholic acids, are excreted from the body.

What role do sequestrants play?

Preparations containing bile acids have a lipid-lowering effect on human body. The use of these drugs artificially reduces the concentration of cholesterol in the blood. Due to the intake of drugs, the risk of developing pathologies of the heart muscle and blood vessels, ischemia, etc. is reduced. Sequestrants are used to provide complex and auxiliary treatment for digestive disorders.

Today, another group of medicines has appeared - statins. They are characterized by increased efficiency and good lipid-lowering properties. The main advantage is the minimum set of side effects.

Metabolism and its dysfunction

Obtaining bile acid of the primary type is carried out in the cytoplasm of the liver cells. After that, they are sent to the bile. The main metabolic process is conjugation, which makes it possible to increase the detergent and amphiphilicity of acid molecules. The enterohepatic circulation of bile consists in the excretion of water-soluble conjugated compounds by the liver tissues. Thus, at the first stage, CoA acid esters of bile are formed.

At the second stage, glycine or taurine is added. Deconjugation occurs when the bile mass enters the ducts inside the liver and is then absorbed by the gallbladder, where it accumulates.

The trapped fats, along with a portion of acidic bile, are partially absorbed by the walls in the gallbladder. The resulting mass enters the duodenal process to accelerate lipolysis. AT intestinal microflora when exposed to enzymes, acids are modified to form secondary forms, which then form the final bile fluid.

Bile circulation in the body healthy person occurs 2 to 6 times in 24 hours. The frequency depends on the power supply. Therefore, out of 15-30 g of bile salts, which is equal to 90%, 0.5 g can be found in the excrement, which corresponds to the daily biosynthesis of cholesterol.

Metabolic disorders lead to cirrhosis of the liver. The amount of cholic acid produced immediately decreases. This leads to malfunctions of the digestive function. Deoxycholic acid is not formed sufficiently. As a result, the daily supply of bile is reduced by half.

Increased bile acidity in the blood affects the decrease in the frequency of pulsations with blood pressure, erythrocytes begin to break down, and the level of ESR decreases. These processes occur against the background of destruction of liver cells, accompanied by jaundice and pruritus.

Reduced amounts of acids in the intestines lead to indigestion of fats obtained from food. The process of absorption of fat-soluble vitamins is disrupted, which leads to hypo- or beriberi with a lack of vitamins A, D, K. A person's blood clotting index decreases due to a lack of vitamin K, it is found a large number of undigested fat in the stool (steatorrhea). With failures in resorption in biliary hepatic cirrhosis, night blindness develops with a lack of vitamin A, osteomalacia with a lack of vitamin D.

Failure in metabolism leads to a weakening of the hepatic absorption of bile. The imbalance leads to the development of cholestasis. This disease is characterized by stagnation of bile in the liver tissues. Reduced quantities do not reach the duodenum.

Often, with cholestasis, there is an increase in intrahepatic concentrations of bile, which contributes to the cytolysis of hepatocytes, which the body begins to attack as detergents. In violation of enterohepatic circulation, the absorption property of acids decreases. But this process is secondary. It is usually caused by cholecystectomy, chronic pancreatitis, celiac disease, cystic fibrosis.

Increased acidity in the stomach is formed when bile enters not into the duodenum, but into gastric juice. You can lower the level of acidity with special preparations - inhibitors. proton pump, which will protect the walls of the stomach from the aggressive effects of bile.