Bile is a product of the activity of hepatocytes (liver cells). Various studies indicate that without the participation of bile in the process of digestion of food, the normal activity of the gastrointestinal tract is impossible. There are violations not only of the digestion process, but also of metabolism, if there is a failure in its production or its composition changes.
What is bile for?
This is the digestive juice produced by the liver. It is used immediately or deposited in the gallbladder. Two important functions of this biologically active liquid are noted. Her:
- helps with the digestion of fats and their absorption in the intestines;
- removes waste products from the blood.
Physical properties
Human bile has a rich yellowish color, turning into greenish-brown (due to the decomposition of dyes). It is transparent, more or less viscous, depending on the length of time it has been in the gallbladder. It has a strong bitter taste, a peculiar smell andafter staying in the gallbladder has an alkaline reaction. Its specific gravity is about 1005 in the bile ducts, but it can rise to 1030 after a long stay in the gallbladder, due to the addition of mucus and some constituents.
Components
Bile, the composition of which is a composition of the following materials: water (85%), bile s alts (10%), mucus and pigments (3%), fats (1%), inorganic s alts (0.7%) and cholesterol (0.3%) is stored in the gallbladder and released into the small intestine through the bile duct after eating.
There is hepatic and cystic bile, their composition is the same, but the concentration is different. During the study, the following substances were found in it:
- water;
- bile acids and their s alts;
- bilirubin;
- cholesterol;
- lecithin;
- sodium, potassium, chloride, calcium ions;
- bicarbonates.
There are 6 times more bile s alts in gallbladder bile than in hepatic bile.
Bile acids
The chemical composition of bile is mainly represented by bile acids. The synthesis of these substances is the main route of cholesterol catabolism in mammals and humans. Some of the enzymes involved in the production of bile acids are active in many cell types in the body, but the liver is the only organ where they are completely converted. Bile acids (their synthesis) are one of the dominant mechanisms for removing excess cholesterol from the body.
However, the withdrawalcholesterol in the form of bile acids is not enough to completely neutralize its excess intake with food. Although the formation of these substances is a cholesterol catabolism pathway, 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 formation requires 17 individual enzymes. Many bile acids are metabolites of cytotoxic substances, so their synthesis must be tightly controlled. Some inborn errors in their metabolism are due to defects in the genes responsible for the synthesis of bile acids, leading to liver failure 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 also regulate overall energy consumption.
Main Functions
Bile contains many different substances. Its composition is such that it does not contain enzymes, as in other digestive juices from the gastrointestinal tract. Instead, it is mostly bile s alts and acids that can:
Emulsify fats and break them into small particles
Help the body absorb the breakdown products of fats in the intestines. Bile s alts bind to lipids and are then absorbed into the bloodstream
Another important function of bile is that it contains destroyed red blood cells. This is bilirubin, and it is usually produced in the body in order to get rid of old red blood cells rich in hemoglobin. Bile also carries excess cholesterol. It is not only a product of liver secretion, but also removes various toxic substances.
How does it work?
The specific composition and function of bile enables it to act as a surfactant, helping to emulsify fats in food in the same way that soap dissolves fat. Bile s alts have a hydrophobic and hydrophilic end. When exposed to water mixed with fat in the small intestine, bile s alts accumulate around the fat droplet and bind both water and fat molecules. This increases the surface area of fat, allowing more access to pancreatic enzymes that break down fat. Because bile enhances fat absorption, it aids in the absorption of amino acids, cholesterol, calcium, and fat-soluble vitamins such as D, E, K, and A.
Alkaline bile acids are also able to neutralize excess intestinal acid before it enters the ileum at the end of the small intestine. Bile s alts are bactericidal, killing many microbes that may 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 act on fats or accumulates in the bladder.
Liverproduces from 600 ml to 1 liter of bile in 24 hours. The composition and properties of bile change as it passes through the bile ducts. The mucous membrane of these formations secretes water, sodium and bicarbonates, thereby diluting the liver secret. These additional substances help to neutralize stomach acid, which enters the duodenum with partially digested food (chyme) from the stomach.
Bile storage
The liver constantly secretes 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 resorption of water, sodium, chlorine and other electrolytes into the blood. Other components of bile, such as bile s alts, cholesterol, lecithin, and bilirubin, remain in the gallbladder.
Concentration
The gallbladder concentrates bile because it can store bile s alts and waste products from the fluid 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 due to the fact that gallbladder bile mainly consists of bile s alts, and bilirubin, cholesterol, lecithin and other electrolytes are absorbed into the blood during their stay in this reservoir.
Bile secretion
20-30 minutes after eating, partially digested food enters the duodenum from the stomach in the form of chyme. The presence of food, especially fatty, in the stomach andin the duodenum stimulates the gallbladder to contract, which is due to the action of cholecystokinin. The gallbladder expels bile and relaxes the sphincter of Oddi, allowing it to enter the duodenum.
Another stimulus for gallbladder contraction is nerve impulses from the vagus nerve and the enteric nervous system. Secretin, which stimulates pancreatic secretion, also enhances bile secretion. Its main effect is to increase the secretion of water and sodium bicarbonate from the bile duct mucosa. This bicarbonate solution, along with pancreatic bicarbonate, is needed to neutralize stomach acid in the intestines.
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 relevance
In the absence of bile, fats become indigestible and are excreted unchanged in the feces. This condition is called steatorrhea. The feces, instead of the characteristic brown color, turns white or gray and becomes greasy. Steatorrhea can lead to a deficiency of nutrients: essential fatty acids and vitamins. In addition, food passes through the small intestine (which is usually responsible for the absorption of fats from food) and changes the intestinal flora. You should know that the processes of processing fats do not occur in the large intestine, which leads to various problems.
BThe composition of bile includes cholesterol, which is sometimes compressed with bilirubin, calcium, forming gallstones. These stones are usually treated by removing the bladder itself. However, they can sometimes be diluted by drugs by increasing the concentration of certain bile acids such as chenodeoxycholic and ursodeoxycholic.
On an empty stomach (after repeated vomiting, for example) the color of the vomit may be green or dark yellow and bitter. This is bile. The composition of the vomit is most often supplemented with normal digestive juices from the stomach. The color of bile is often compared to the color of "freshly cut grass", in contrast to the components in the stomach, which appear greenish yellow or dark yellow. Bile can enter the stomach from a weakened valve, certain drugs, alcohol, or strong muscle contractions and duodenal spasms.
Bile study
Bile is examined by the method of separate probing. The composition, quality, color, density and acidity of various portions allows us to judge violations in synthesis and transportation.
