Bile is a product of the activity of hepatocytes (liver cells). Various studies indicate that without the participation of bile in the process of digesting food, normal gastrointestinal activity is impossible. Violations occur not only in the digestion process, but also in metabolism, if a failure occurs in its production or its composition changes.
What is bile 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 fluid are noted. It:
- helps the digestion of fats and their absorption in the intestines;
- removes waste products from the blood.
Physical properties
Human bile has a saturated yellowish color, turning into a greenish-brown (due to the decomposition of dyes). It is transparent, more or less viscous, depending on the length of time spent in the gallbladder. It has a strong bitter taste, a peculiar smell 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 long 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%) , is stored in the gallbladder and, after eating, is discharged into the small intestine through the bile duct.
There is hepatic and cystic bile, their composition is the same, but their concentration is different. During 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 gallbladder bile salts of bile acids are 6 times more than in liver.
Bile acids
The chemical composition of bile is mainly represented by bile acids. The synthesis of these substances is the main pathway of cholesterol catabolism in 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 they undergo complete transformation. 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 its excess intake with food. Although the formation of these substances represents a pathway for cholesterol catabolism, these compounds are also important in the solubilization of cholesterol, lipids, fat-soluble vitamins and other essential substances, thereby facilitating their delivery to the liver. The entire bile acid production cycle requires 17 individual enzymes. Many bile acids are metabolites of cytotoxic substances, so their synthesis should be tightly controlled. Some congenital disorders of their metabolism are caused by defects in the genes responsible for the synthesis of bile acids, which leads 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 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 down into small particles.
- To help the body absorb the breakdown products of fats in the intestines. Bile salts bind to lipids and are then absorbed into the blood.
Another important function of bile is that it contains broken red blood cells. This is bilirubin, and it is usually formed 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 functions of bile enable it to act as a surfactant, helping to emulsify fats in food in the same way that soap dissolves fat. Bile salts have a hydrophobic and hydrophilic end. When exposed to water mixed with fat in the small intestine, bile salts accumulate around a 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 enhances the absorption of fats, it helps in the process of 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 in the final portion of the small intestine. Bile salts have a bactericidal effect, destroying many microbes that may be present in incoming food.
Bile secretion
Liver cells (hepatocytes) produce bile, which accumulates and flows into the bile duct. From here, it passes into the small intestine and immediately begins to act 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 mucosa of these formations secrete water, sodium and bicarbonates, thereby diluting the liver secretion. These additional substances contribute to the neutralization of 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 drive - the gall bladder. This hollow organ concentrates it by the resorption of 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 toxins 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 cystic bile consists mainly of bile salts, and bilirubin, cholesterol, lecithin and other electrolytes are absorbed into the blood during their stay in this reservoir.
Bile secretion
After 20-30 minutes after eating, partially digested food enters the duodenum from the stomach in the form of a chyme. The presence of food, especially fatty, in the stomach and duodenum stimulates the gallbladder to contract, due to the action of cholecystokinin. The gall bladder displaces bile and relaxes the sphincter of Oddi, thereby allowing it to enter the duodenum.
Another stimulus for contracting the gallbladder is nerve impulses from the vagus nerve and enteric nervous system. Secretin, which stimulates the secretion of the pancreas, also enhances bile secretion. Its main effect is an increase in the secretion of water and sodium bicarbonates from the mucosa of the bile duct. This bicarbonate solution along with pancreatic bicarbonate is necessary to neutralize the stomach acid in the intestines.
Bile contains various substances - proteins, amino acids, vitamins and a number of others.
It should be noted that for 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 excreted unchanged in the feces. This condition is called steatorrhea. Feces instead of the characteristic brown color turn white or gray and become bold. 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 alters the intestinal flora. You should be aware that fat processing does not occur in the large intestine, which leads to various problems.
Bile contains cholesterol, which is sometimes compressed with bilirubin, calcium, forming gallstones. These calculi are usually treated by removing the bladder itself. However, they can sometimes be dissolved with 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 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,” unlike 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.
Bile test
Using separate sensing, bile is examined. The composition, quality, color, density and acidity of various portions allows us to judge violations in the synthesis and transportation.