Bile: composition and properties. Chemical composition of bile

Bile is a product of the activity of hepatocytes (liver cells). Various studies indicate that without the involvement of bile in the process of digestion of food, normal gastrointestinal activity is impossible. There are violations not only of digestion, but also of metabolism, if a failure occurs in its development or its composition changes.

What is bile used for?

This is the digestive juice that is produced by the liver. It is used immediately or deposited in the gallbladder. Two important functions of this biologically active liquid are noted. She is:

• Helps digestion of fats and their absorption in the intestine;
• Removes the waste products from the blood.

Physical properties

The human bile has a rich yellowish color, which turns into a greenish-brown color (due to decomposition of coloring substances). It is transparent, more or less viscous, depending on the duration of time in the gallbladder. It has a strong bitter taste, a peculiar odor and after being in the gallbladder has an alkaline reaction. Its specific gravity is about 1005 in the bile ducts, but it can grow to 1030 after a prolonged stay in the gallbladder, due to the addition of mucus and some components.

Components

Bile, the composition of which is a composition of the following materials: water (85%), bile salts (10%), mucus and pigments (3%), fats (1%), inorganic salts (0.7%) and cholesterol (0.3%) , Stored in the gallbladder and after eating is thrown into the small intestine through the bile duct.

There is hepatic and gall bladder, their composition is the same, but the concentration is different. In the study, the following substances were found in it:

• water;
• Bile acids and their salts;
• bilirubin;
• cholesterol;
• lecithin;
• Ions of sodium, potassium, chlorine, calcium;
• Bicarbonates.

In the gallbladder bile salts of bile acids is 6 times more than in the hepatic.

Bile acids

The chemical composition of bile is mainly represented by bile acids. Synthesis of these substances is the main way of catabolism of cholesterol in the body of mammals and humans. Some enzymes involved in the production of bile acids are active in many types of body cells, but the liver is the only organ where their complete transformation takes place. Bile acids (their synthesis) are one of the dominant mechanisms for removing excess cholesterol from the body.

However, excretion of cholesterol in the form of bile acids is not enough to completely neutralize the excess supply of it with food. Although the formation of these substances is the pathway of catabolism of cholesterol, these compounds are also important in solubilizing cholesterol, lipids, fat-soluble vitamins and other essential substances, thereby facilitating their delivery to the liver. The entire cycle of bile acid production requires 17 individual enzymes. Many bile acids are metabolites of cytotoxic substances, therefore their synthesis must be under strict control. Some congenital disorders of their metabolism are caused by defects in genes responsible for the synthesis of bile acids, which leads to hepatic insufficiency in early childhood and progressive neuropathy in adults.

Recent studies have shown that bile acids are involved in the regulation of their own metabolism, regulate lipid metabolism and glucose metabolism, are responsible for controlling various processes in liver regeneration, and regulate the total energy expenditure.

Main functions

Many different substances contain bile. Its composition is such that there are no enzymes in it, as in other digestive juices from the gastrointestinal tract. Instead, it is mainly represented by bile salts and acids, which can:

• Emulsify fats and break them into small particles.

• Help the body absorb the products of the decomposition of fats in the intestines. Salts of bile acids bind to lipids and then are absorbed into the blood.

Another important function of bile is that it contains destroyed erythrocytes. This is bilirubin, and usually it is formed in the body in order to get rid of the old red blood cells, rich in hemoglobin. Bile also tolerates excess cholesterol. It not only is a product of liver secretion, but also displays various toxic substances.

How does it work?

The specific composition and function of the bile gives it the ability to act as a surfactant, helping to emulsify fats in food just like soap dissolves fat. Bile salts have a hydrophobic and hydrophilic end. When water is mixed with fat in the small intestine, bile salts accumulate around the fat drop and bind both water and fat molecules. This increases the surface area of fat, providing greater access to pancreatic enzymes that break down fats. Since bile increases the absorption of fats, it helps in the absorption of amino acids, cholesterol, calcium and fat-soluble vitamins such as D, E, K and A.

Alkaline bile acids are also capable of neutralizing excess intestinal acid before it enters the ileum at the terminal site of the small intestine. Salts of bile acids have a bactericidal effect, destroying many microbes that can be present in incoming food.

Bile secretion

Liver cells (hepatocytes) produce bile, which accumulates and drains into the bile duct. From here it passes into the small intestine and immediately begins to work on fats or accumulates in the bladder.

The liver produces from 600 ml to 1 liter of bile in 24 hours. The composition and properties of bile change when it passes through the bile ducts. The mucous membrane of these formations secrete water, sodium and bicarbonates, thereby diluting the hepatic secret. These additional substances help neutralize stomach acid, which enters the duodenum with partially digested food (chyme) from the stomach.

Bile storage

The liver constantly secrets bile: up to 1 liter in a 24-hour period, but most of it is stored in the gallbladder. This hollow organ concentrates it by resorbing water, sodium, chlorine and other electrolytes into the blood. Other components of bile, such as bile salts, cholesterol, lecithin and bilirubin, remain in the gallbladder.

Concentration

The gallbladder concentrates bile because it can store bile salts and slags from the liquid produced by the liver. Components such as water, sodium, chlorides and electrolytes, then diffuse through the bubble.

Studies have shown that the composition of human bile in the bladder is the same as in the liver, but 5-20 times more concentrated. This is explained by the fact that the gallbladder mainly consists of bile salts, and bilirubin, cholesterol, lecithin and other electrolytes are absorbed into the blood during the stay in this tank.

Bile secretion

After 20-30 minutes after eating, partially digested food enters the 12-colon from the stomach in the form of chyme. The presence of food, especially oily, in the stomach and duodenum stimulates the gall bladder to contract, which is due to the action of cholecystokinin. The gallbladder displaces bile and relaxes the sphincter of Oddi, thereby allowing it to enter the duodenum.

Another incentive for contraction of the gallbladder is nerve impulses from the vagus nerve and the enteral nervous system. Secretin, which stimulates the secretion of the pancreas, also increases bile secretion. Its main effect is an increase in the secretion of water and sodium bicarbonate from the bile duct mucosa. This bicarbonate solution, together with pancreatic bicarbonate, is necessary to neutralize gastric acid in the intestine.

Bile contains various substances - proteins, amino acids, vitamins and a number of others.

It should be noted that in different people, bile has an individual qualitative and quantitative composition, that is, it differs in the content of bile acids, bile pigments and cholesterol.

Clinical Significance

In the absence of bile, fats become indigestible and remain unchanged in feces with feces. This state is called steatoria. Cal instead of the characteristic brown color is painted in a white or gray shade and becomes fat. Steatorea can lead to a deficiency of nutrients: essential fatty acids and vitamins. In addition, the food passes the small intestine (which is usually responsible for the absorption of fats from food) and changes the flora of the intestine. You should know that in the large intestine there are no processes of processing of fats, which leads to various problems.

The composition of the bile includes cholesterol, which sometimes is compressed with bilirubin, calcium, forming gallstones. These concretions, as a rule, are treated by removing the bladder itself. However, they can sometimes be dissolved by drugs with an increase in the concentration of certain bile acids, such as chenodeoxycholic and ursodeoxycholic.

On an empty stomach (after repeated vomiting, for example), the color of vomiting can be green or dark yellow and with bitterness. This is bile. The composition of vomit is most often supplemented with normal digestive juices from the stomach. The color of bile is often compared to the color of "freshly mown grass", in contrast to the components in the stomach that look greenish-yellow or dark yellow. Bile can enter the stomach due to a weakened valve, when taking certain drugs, as well as alcohol, or under the influence of powerful muscle contractions and spasms of the duodenum.

Examination of bile

By the method of separate probing, bile is examined. The composition, quality, color, density and acidity of the various portions allows to judge the violations in the synthesis and transportation.