Bile

Bile represents the secretion of liver cells, including apparently also Kupffer cells. As it passes through the bile ducts and during its stay in the gallbladder, the bile secreted by the liver cells (hepatic bile) undergoes a series of changes: the mucous, mucin-rich (or mucin-like nucleoalbumin) secreted by the epithelium of the bile ducts and gallbladder gives the initially liquid and transparent hepatic bile a viscous, sticky character. Gallbladder bile is usually turbid due to admixed epithelial cells, precipitated calcium compounds of bile pigments, etc. In the gallbladder, vigorous absorption of water occurs, as a result of which the concentration of bile increases 5-10 times. The increase in concentration does not affect mineral salts, which are absorbed along with water, so their content in hepatic and gallbladder bile is almost the same. Composition of human bile (according to Hammarsten). Components of 1,000 parts of bile contain: hepatic bile, gallbladder bile. Solids: Mucin and pigments, Bile acid salts, Fatty acids from soaps, Cholesterol. 35.260, 25,400, 964,740, 974,600, 4,290, 5,150, 18,240, 9,040, 1,360, 1,010, 1,600, 1,500, 0.574, 0.650, 0.958, 0.610, 7,250, 7,460, 170,320, 160,200, 829,860, 839,800, 41,910, 44,370, 96,970, 87,230, 11,170, 10,580, 9,860, 8,700, 2,230, 1,410, 1,900, 6,500, 5,100, 5,380. Depression (freezing point lowering) of gallbladder bile - from -0.54° to -0.63°; pH of hepatic bile - 7.3-5.0, of gallbladder bile - 6.8; specific gravity of hepatic bile - 1.003-1.006, of gallbladder bile - 1.008-1.040. In bile, in addition to bile acids and bile pigments (see below), lecithin, lecithin, cholesterol, soaps, fatty acids, ethyl sulfuric acids (in very small amounts in humans), urea (23.5-40 mg%), traces of paired glucuronic acids; the presence of uric acid cannot yet be considered established. Among the mineral components, in addition to the alkalis that are part of the bile acid salts, bile contains sodium and potassium chlorides, phosphates, calcium, magnesium, traces of copper, sometimes traces of zinc. Iron is always present in bile (0.04-0.11%_o). The opinion of some authors that iron is excreted with bile, coming from food, is disputed by other researchers. With bile, a number of medicinal substances can be excreted, for example, iodides, alkaloids, salicylates, etc. Certain enzymes have been found in bile - amylase, catalase, oxidase. Their quantity is insignificant, and it is hardly possible to attribute any physiological significance to them. The reaction of bile, conditioned by the content of buffer salts and appearing weakly alkaline to litmus, is actually close to neutral or even slightly acidic. The color of bile, depending on the content of one or another of the bile pigments (see below), can be very different; in humans, bile is usually golden-yellow, sometimes with a brownish tint, but it can also be green. The taste, depending mainly on the bile acid salts, is bitter with a subsequent sweetish aftertaste. Various values are given for the exact amount of bile, usually around 1,000 cm³. However, by means of a duodenal tube, up to 4,000 cm³ could be obtained per day. Due to the significant thickening of bile in the gallbladder, the volume of bile actually secreted by the liver many times exceeds the amount excreted into the intestinal canal. Just like urination, the excretion of bile ceases when its outflow from the bladder or ducts is obstructed and pressure in the latter increases. The cessation of bile secretion occurs at a pressure of about 350 mm of water, i.e., approximately three times less than is required to stop urination. Part of the bile entering the intestine is absorbed into the blood and through the portal vein again enters the liver, thus performing the so-called enterohepatic circulation. The latter is undoubtedly established for bile acids; to what extent other components of bile participate in it is not yet finally established.

V. Engelhardt. Bile acids, the specific component of bile, are produced in the liver and are found in the organism mainly in the form of sodium salts. Most of them consist of 2 components (paired bile acids), one of which (cholic acids) is characteristic of bile acids. Cholic acids are crystalline, similar in structure to sterols, monobasic oxyacids, derivatives of the hydrocarbon cholane C₂₄H₄₀, containing 4 hydroaromatic rings. Cholic acids and paired bile acids give many color reactions, such as: 1) the Pettenkofer reaction - cherry-red coloring when mixing their aqueous solution containing a small amount of cane sugar with concentrated H₂SO₄; the liquid, diluted with alcohol, shows 2 absorption bands near the Fraunhofer lines E and F; 2) a red-brown liquid with green fluorescence when dissolved in concentrated H₂SO₄.-Cholic acid (cholalic, trihydroxycholanic acid), C₂₄H₄₀(OH)₃.COOH, is found in intestinal stones, in small amounts in intestinal contents. It is formed from glycocholic and taurocholic acids of bile during putrefaction in the intestine, during hydrolysis. Melting point 196-198°; [a]_D= +37.02° (in alcoholic solution). Solubility in cold water 1:4,000, in boiling water-1:750, in 70% alcohol-1:20, in ether-1:27. Sweetish-bitter taste. Alkali salts are easily soluble in water, lead and silver salts are almost insoluble. When heating cholic acid, boiling with acids, putrefaction in the intestine, anhydride of delysin, C₂₄H₃₆O₃, is formed, which is found in feces - an amorphous, water-insoluble substance. Cholic acid, in addition to reactions common to bile acids, gives a reaction specific to it, the Millius reaction: an alcoholic solution of cholic acid, mixed with a solution of iodine, when carefully diluted with water becomes blue and releases microscopic blue needles.-Deoxycholic (dihydroxycholanic) acid, C₂₄H₄₀(OH)₂.COOH, is found in ox bile (0.7%), in ox gallstones, in feces. Melting point 172°; [a]_D= +57.02° (in alcoholic solution). Bitter taste, difficult to dissolve in water, easily in alcohol. It has the remarkable ability to form difficultly separable addition compounds with higher fatty acids (such compounds were previously described under the name of choleic acid of bile) and with many other organic substances. This ability has great physiological significance, as in this way many water-insoluble substances (cholesterols, fatty acids, alkaloids, etc.) are converted into a water-soluble, absorbable form.-Lithocholic (monohydroxycholanic) acid, C₂₄H₃₈(OH).COOH, is found in gallstones, in hydrolyzed ox bile (0.002%). Melting point 186°; [a]_D= +32.72° (in alcoholic solution). Tasteless, easily soluble in alcohol; water-insoluble alkali salts are very easily soluble in the presence of the sodium salt of deoxycholic acid. From the point of view of comparative biological chemistry, it is of interest that in some species of animals there are special cholic acids. Thus, during hydrolysis of the bile of walruses and seals, two phocholic acids are isolated, from pig bile-2 gnocholic acids, from goose-cholalic acid. The bile acids of polar sharks include instead of cholic acid 2 scymnols, C₂₇H₄₆O₅ and C₂₇H₄₈O₄-alcohols, closely related to cholic acid. The composition of bezoars (see) includes special bile acids: lithophellinic and lithobilinic. Paired bile acids are compounds of cholic acids with glycine or taurine, as well as scymnols with sulfuric acid. Derivatives of glycine are difficult to dissolve in water, ether, chloroform, benzene, easily soluble in alcohol. Alkali salts are easily soluble in water, other salts are difficult to dissolve or insoluble.-Glycocholic acid, C₂₆H₄₃O₆N, is found in the bile of many animals, including humans; absent in dog bile; very little of it in fish bile. Sometimes found in feces, in jaundice-in urine. Synthetically obtained from the azide of cholic acid and glycine. Needles with a sweetish-bitter taste, [a]_D=+32.3° (in alcoholic solution). Solubility in cold water 0.33:1,000, in boiling water-8.5:1,000. Decomposed by alkalis into cholic acid and glycine. With prolonged boiling of an aqueous solution, it passes into the isomeric paraglycocholic acid.-Glycocholic acid (glycodeoxycholic acid), C₂₆H₄₃O₆N, is found in human, ox, and musk ox bile. Needles or prisms with melting point 175-176°, bitter taste. In pig bile, two hyoglycocholic acids are found. Derivatives of taurine (except phoctaurine cholic acids) are easily soluble in water and alcohol, insoluble in ether, benzene, acetone, chloroform.-Taurocholic acid, C₂₆H₄₅NO₇S, is contained in human bile and many other animals. In jaundice, it is found in urine, in diarrhea-in feces. Synthetically obtained from the azide of cholic acid and taurine. Crystallizes in prisms with 1H₂O. Sweet taste with a very slight bitter aftertaste. It has the ability to keep glycocholic acid in solution, precipitates acidic protein solutions. For sodium salt [a]_D =+23.27°. More easily than glycocholic acid, it is cleaved during hydrolysis into taurine and cholic acid.-The quantitative ratio of glycocholic and taurocholic acids in the bile of various animals varies greatly. In humans, in hepatic bile, 0.9-1.8% salts of paired bile acids are contained, in gallbladder 5.7-10.8%. Under pathological conditions, for example, in amyloid of the liver, cases of almost complete absence of bile acids have been observed. In addition to the cases mentioned above, bile acids are found in meconium, vomit, in traces in normal urine (?), blood. Paired bile acids are synthetically formed in the liver from cholic acids and glycine or taurine. The material for the formation of cholic acids has not yet been clarified; it is possible that it is cholesterol. Glycine is formed during the cleavage of a protein molecule, taurine - during the oxidation of cystine and cysteine of proteins. The breakdown products of paired bile acids are partly absorbed in the intestine and again serve in the liver as material for the synthesis of bile acids. Part of the bile acids, not subjected to cleavage, is absorbed and, entering the liver, is again excreted with bile (bile circulation). Bile acids are absorbed in the jejunum and ileum, but not in the duodenum; in the jejunum only glycocholic acid is absorbed, but not taurocholic acid. Cholic acid and paired bile acids enhance the digestive effect of pancreatic juice enzymes, convert the zymogen of steapsin into an active form, enhance peristalsis of the large intestine. Free taurocholic and glycocholic acids have an antiseptic effect. They cause hemolysis and when introduced into the blood, they show a poisonous effect.-To detect bile acids in urine, it is evaporated, the residue is extracted with alcohol, the extract is evaporated to dryness, the residue is extracted with absolute alcohol, the filtrate is evaporated, the residue is dissolved in water, the solution is carefully precipitated with lead acetate with the addition of ammonia. The filtered and pressed precipitate is extracted with boiling absolute alcohol, the extract is evaporated with soda and extracted with absolute alcohol. With the alcoholic extract containing sodium salts of bile acids, the Pettenkofer reaction is performed. Bile pigments, derivatives of pyrrole, have the properties of acids, dissolve in alkalis, give difficultly soluble salts with alkaline earths and heavy metals. Unlike blood pigments, they do not contain iron, with the exception of bilicyanin and cholethelin, they do not give absorption bands in the spectrum. They enter as a specific part into the composition of bile. In the bile of all vertebrates studied, in some animals, including humans, there is a red-brown bilirubin, in others-green biliverdin, often urobilin and urobilinogen. In bile concretions, in corpse bile, and under some pathological conditions, in addition to bilirubin and biliverdin, choleprazine, bilifuscin, biliprazine, biligumin, bilicyanin, cholethelin, etc. are found.-Bilirubin, C₃₃H₃₆N₄O₆, in the molecule of which there are 4 pyrrole rings, besides bile, is found in the contents of the small intestines, in blood serum (up to 1.1 mg per 100 cm³), in places of old hemorrhages, in urine and tissues in jaundice, in the form of calcium and magnesium salts in gallstones, in meconium, in the feces of infants, in the feces of adults under pathological conditions, in sputum in jaundice, in pneumonia, during the autopsy of a liver abscess, echinococcus, or empyema in the lung. Many types of hematoidins are identical with bilirubin. Bilirubin is obtained from ox gallstones. It exists in two modifications: 1) ordinary-orange and 2) slightly more soluble-red-brown. Bilirubin does not melt even at 400°, is insoluble in water, glycerin, very little soluble in ether, benzene, carbon disulfide, amyl alcohol, somewhat more easily-in alcohol.

Solubility in dimethylaniline 1:100, in chloroform 1:120-1:450, depending on origin. From a chloroform solution, bilirubin crystallizes in rhomboid tablets. The ammonium salt, C₃₃H₃₈O₆N₄.NH₃, crystallizes well from methyl alcohol. Alkaline salts are insoluble in chloroform, and when shaken with solutions of caustic alkalis, bilirubin can be removed from the chloroform solution (difference from lipochromes). Bilirubin is easily altered, especially under the influence of oxidizing agents, on which Gmelin's reaction is based (see Gmelin's test). For the detection of bilirubin, the diazo reaction, Gmelin's reaction, and Hammarsten's reaction are used: persistent green coloring when several drops of bilirubin solution are mixed with several drops of reagent (a yellowed mixture of 1 volume of 25% HNO₃ with 19 volumes of 25% HCl; before use, 1 volume of the mixture is mixed with 4 volumes of alcohol). With further addition of the acid mixture, the coloring becomes blue, violet, then red and brown. The sensitivity of the reaction is 1:500,000-1,000,000. In the presence of blood pigments and urobilin, the most reliable is the Guppert-Zalkovsky reaction: bilirubin is precipitated from the test liquid as calcium salt by adding lime milk or a CaCl₂ solution, then a solution of soda or ammonia. The washed precipitate is boiled with alcohol containing 5% strong HCl; a blue-green coloring is obtained. Among the oxidation products of bilirubin is the imide of hematinic acid, C₈H₉O₄N, which is also formed during the oxidation of hematin. Upon reduction of bilirubin, hematopyrroles and hematopyrrolecarboxylic acids are obtained, as in the reduction of hematin. From the products of incomplete reduction of bilirubin, mesobilirubin, C₃₃H₄₀O₆N₄, and its colorless chromogen mesobilirubinogen, C₃₃H₄₁O₆N₄ (otherwise hemibilirubin), identical with urinary urobilinogen, should be noted. In the body, this reduction occurs under the influence of intestinal bacteria. Biliverdin, C₃₃H₃₆O₈N₄(?), is an oxidation product of bilirubin. It is found in the bile of many animals, especially during fasting, in vomit, in the shells of some bird eggs, sometimes in urine in jaundice, and occurs in small quantities in gallstones. It differs from bilirubin by its green color, solubility in alcohol, and insolubility in chloroform; it does not give the diazo reaction. It is obtained by oxidation of bilirubin by atmospheric oxygen in an alkaline medium. A similar-looking pigment is formed when halogens act on bilirubin. Other bile pigments, found mainly in gallstones, have not yet been obtained in pure form, and even the existence of some of them is questionable. In the bile of herbivores, the pigment phylloerythrin (cholohematin, bilipurpurin), a derivative of chlorophyll, is often found. Substances close to bile pigments have been found in the shells of some mollusks, in bezoars. With the exception of phylloerythrin, which is formed in the intestine from chlorophyll, bile pigments arise in the body from the colored part of the blood pigment molecule. When introduced into the blood or when it passes from erythrocytes into plasma (during hemolysis), the formation of bile pigments increases, and jaundice may occur. When injected under the skin, hematin is almost completely excreted in the form of bile pigments with B. The relationship between hematin and bilirubin is established from the commonality of their cleavage products. The main site of formation of bile pigments is the liver (apparently its Kupffer's star-shaped cells), but the formation of bile pigments can also occur in other organs and tissues, especially in the reticuloendothelial apparatus. The finding of bilirubin in the sites of old hemorrhages, the formation of bile pigments in the spleen in hemolytic anemia and in some poisonings (phenylhydrazine), and the formation of bilirubin from hematin in serous cavities speak in favor of this. When injected into the blood in a dose of 0.05 g per 1 kg of body weight, bilirubin has a poisonous effect. For the detection of bile pigments in animal tissues and protein-containing fluids, in most cases, the alcoholic extract of tissues or the alcoholic filtrate from the protein precipitate can be tested with the reactions indicated above. In human bile, there is approximately 0.4-1.3°/₀₀, on average 0.5°/₀₀ of bilirubin, in dog bile 0.6-0.7°/₀₀. Per 1 kg of animal, no more than 7 mg of pigment is excreted in 24 hours. In gallbladder bile, the pigment content is 3-7 times greater than in liver bile. The pigment content in the daily amount of bile in humans is estimated at 0.2-2 g. For quantitative determination of bilirubin, spectrophotometric and colorimetric methods, l. Brode, are used. The physiological significance of bile is determined by its role in intestinal digestion. Due to the presence of a relatively large amount of buffer salts, bile, encountering the acidic food porridge coming from the stomach in the duodenum, neutralizes the acidity to a large extent and facilitates the action of the enzymes of pancreatic juice. The direct activating effect of bile, particularly bile acids, on the enzymes of the pancreas—trypsin, amylase, and lipase—formerly accepted by authors, is now denied. In relation to trypsin and amylase, the matter apparently comes down to a corresponding change in the reaction of the medium. Even with a complete cessation of bile entering the intestine (dogs with fistulas), the digestion of proteins and carbohydrates proceeds normally. For the digestion and absorption of fats, however, the presence of bile is very important. The action of bile here manifests itself in several directions. Emulsifying action is usually attributed great importance; due to the content of fatty acids with high surface activity, bile promotes the breakdown of fats entering the intestine into the smallest droplets and imparts stability to the resulting emulsion. Thus, the surface exposed to the action of the enzyme significantly increases. However, judging by recent works from Willstätter's laboratory, emulsification does not play a particularly large role, since other emulsifying agents, for example albumin, not only do not increase but even inhibit fat breakdown. It has now been refuted that bile acid salts are kinases that convert the inactive zymogen of lipase into an active form. According to Willstätter's research, the action of bile acid salts consists in that they form colloidal precipitates with the proteins present in the intestine, simultaneously adsorbing both the substrate and the enzyme. The latter in such a 'complex adsorbate' manifests its maximum activity. In addition to influencing the enzymatic breakdown of fats, bile acids also play an essential role in the further absorption of digestion products. Of particular importance is the ability of bile acids to form compounds with fatty acids, the so-called choleic acids, easily soluble in water. The fatty acids formed during the digestion of fats are found in the intestine not only in the form of soaps but also to a large extent in the free, completely water-insoluble form. These free fatty acids are transferred to a soluble state and become accessible for absorption and utilization solely due to the presence of bile acid salts. With insufficient bile entering the intestine, putrefactive processes develop strongly in it. However, this is not due to the loss of the disinfecting effect of bile, as was previously believed (bile can even serve as a nutrient medium for bacteria), but to the fact that fatty acids, the absorption of which in the intestine ceases in the absence of bile, serve as a nutrient material for bacteria and thus promote their multiplication. V. Engelhardt. The pathology of bile secretion and excretion is reduced to: 1) decreased secretion—acholia (see) or hypocholia; 2) increased secretion (polycholia, pleiochromia); 3) changes in bile when it accumulates in the gallbladder and ducts; 4) the excretion of foreign pathological products with bile. For details on the pathology of bile, its secretion and excretion—see Liver. Deposition in organs. The deposition of bile in organs is observed mainly in jaundice (see), in which case it occurs both in the liver and in other organs. In the liver in obstructive jaundice, the deposition of bile is noticeable in the dilated bile capillaries, where it, thickening, forms bile thrombi and cylinders; in addition, bile pigments are deposited in the liver and Kupffer's cells in the form of small grains. In other organs in jaundice, there is mainly diffuse impregnation with bile; only in the endothelium of the sinuses of regional lymph glands to the liver, as well as in the epithelial cells of the kidney tubules, does the deposition of bile occur in the form of small grains, and in the kidneys, the breakdown of cells loaded with bile pigments results in the formation of bile cylinders in the tubules.

In severe jaundices accompanying acute yellow atrophy of the liver and certain septicopyemias, deposition of bilirubin crystals in organs was sometimes observed; however, this is apparently a postmortem phenomenon; deposition of bile pigment crystals into tissue during life occurs only in newborns in the case of infarction of the kidneys. (On the effect of deposits of B. on living tissue—see Jaundice.) Besides jaundice, deposition of B. in organs can be observed in all cases where B. comes into contact with any dead substrate; in this case, B. impregnates the dead mass. Thus, in the liver, when the bile ducts are destroyed by the process of suppuration, which occurs in cholangitis (see) and abscesses of the liver of various origins, B. is deposited in the necrotic masses of exudate or in the dead liver tissue, coloring them orange-yellow; tubercular cheesy foci, dead nodes of multilocular echinococcus, and dead areas of liver tumors are also impregnated with bile when the bile ducts are destroyed by these processes. Something similar also occurs in the intestine, where any dead substrate (e.g., Peyer's patches during the necrotization period in typhoid fever, deposits on the mucosa in dysentery, etc.) is stained by the bile present in the intestinal contents. Finally, B. pouring into the abdominal cavity during rupture of the gallbladder can be deposited in the fibrinous masses of exudate, coloring them yellow.

A. Abrikosov. Bile as a nutrient medium was first applied in bacteriological practice by Conradi in 1904. He proved that B. is a particularly favorable medium for the development of typhoid bacteria when seeding blood from typhoid fever patients. The advantage of this medium is that, by dissolving the formed elements of blood, B. simultaneously destroys its bactericidal properties; consequently, unlike other methods of blood seeding, there is no need to use large amounts of nutrient medium; for seeding 2.5-5 cm³ of the blood under study, 5-10 cm³ of B. is sufficient. The multiplication of typhoid bacteria in B. occurs extremely vigorously, and due to this, even if only a negligible amount of them is present in the blood, it will be possible to obtain a culture. Being an elective medium for typhoid bacteria, B. simultaneously possesses bactericidal properties with respect to some other microbes, which reduces the danger of accidental contamination during blood seeding. The bactericidal properties of bile, as well as bile acid salts, are clearly expressed with respect to pneumococci and Streptococcus mucosus. These microbes dissolve upon the addition of 0.1 cm³ of B. to 1-2 cm³ of broth.—B. for blood seeding is prepared as follows: the contents of the gallbladder from a healthy animal are drawn with a sterile pipette into a sterile flask and sterilized in an autoclave at 105-110° for 30 min.; then it is filtered through cotton wool, poured into tubes in 5-10 cm³ portions, and sterilized again. Conradi recommends adding 10% peptone to freshly obtained B. to increase the nutritive value of the medium and to prevent the clotting of blood, and 10% glycerin to delay the growth of saprophytes in case of accidental contamination. These modifications, however, do not significantly affect the results. In the case where a blood clot is seeded rather than fresh blood, Kirstein advises adding to 5 cm³ of B. 0.1-0.3 cm³, depending on the size of the clot, a concentrated glycerin solution of trypsin. Calmette and Guerin used potato with bile as a nutrient medium for subcultures of tubercle bacilli with the aim of reducing their virulence. As a result of prolonged subcultures, the BCG culture was obtained. As a component of B., it enters into Padlevsky's agar, which is a colored nutrient medium for differentiating typhoid bacteria and the colon bacillus.