Liver function

The liver is the largest organ in humans. The functions of the liver are varied. It is involved in the processes of digestion, hematopoiesis and performs numerous functions in metabolism.

The liver is located in the right hypochondrium and epigastric region; it has diaphragmatic and visceral surfaces. These surfaces converge with each other, forming a sharp lower edge of the liver. The left (smaller) and right (larger) lobes of the liver are distinguished, consisting of the square and caudate lobes. The falciform ligament, which separates the right and left lobes in front, goes from the diaphragm and the anterior abdominal wall to the diaphragmatic surface of the liver. Behind, they are separated by a gap in which the ligamentum venosum passes (an overgrown venous duct that connected the nocturnal vein with the inferior vena cava in the fetus).

Below, the liver lobes are divided by a fissure where the round ligament of the liver (overgrown umbilical vein) passes. At the level of the posterior edge of the fissure of the round ligament and the gallbladder fossa are the liver gates. The portal vein, proper hepatic artery, and nerves enter them; the common hepatic duct and lymphatic vessels emerge from them.

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Digestive function of the liver

Bile, produced by the liver, plays an important role in digestion processes, providing a change from gastric to intestinal digestion (I.P. Pavlov). Bile inactivates pepsin, neutralizes hydrochloric acid found in the gastric contents, and also increases the activity of pancreatic enzymes. Bile salts emulsify fats, which leads to their further digestion. Bile promotes the active work of enterocytes and their regeneration

In addition, it is involved in stimulating intestinal motility and inhibits the growth of opportunistic microflora, which prevents the development of putrefactive processes in the intestines.

The liver of a healthy adult produces 0.6-1.5 liters of bile per day, 2/3 of which are formed as a result of the activity of hepatocytes and 1/3 - epithelial cells of the bile ducts. Bile contains bile acids, bile pigments, cholesterol, inorganic salts, soaps, fatty acids, neutral fats, lecithin, urea, vitamins A, B, C and a small amount of amylase, phosphatase, protease, catalase, oxidase.

There are two mechanisms involved in the production of bile by hepatocytes: dependent and independent of bile acids. The final formation of primary bile occurs in the bile ducts. Hepatic bile differs in composition from gallbladder bile, since bile in the gallbladder is exposed to its epithelium. Reabsorption of water and some ions occurs, which leads to an increase in the concentration of gallbladder bile. This is why, although the normal volume of the gallbladder of an adult is 50-60 ml, it can accommodate bile produced by the liver for about half a day. In this case, the pH of gallbladder bile usually decreases to 6.5 against 7.3-8.0 of gallbladder bile. Bile formation (choleresis) occurs continuously, including during fasting.

Bile excretion (cholekinesis) is regulated by the work of the sphincters of the biliary tract and the muscles of the gallbladder. Outside the digestion process, bile accumulates in the gallbladder, since the sphincter of the common bile duct (Oddi) is closed, and bile cannot enter the duodenum. Then the sphincter of Mirizzi, located at the junction of the common hepatic and cystic ducts, and the sphincter of Lutkens in the neck of the gallbladder are open. After eating, the sphincter of Oddi opens, and the contractile activity of the gallbladder and bile ducts increases. First, cystic bile enters the duodenum, then mixed bile, and then liver bile.

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Non-digestive function of the liver

The liver plays an exceptional role in ensuring specific reactions of protein, carbohydrate, fat, and mineral metabolism.

Proteins are synthesized in the liver - fibrinogen, prothrombin, other factors that provide hemostasis and anticoagulation mechanisms, almost all albumins, globulins, and glycogen. With an increase in the body's energy expenditure, glycogen is broken down to form glucose. The liver's participation in maintaining the concentration of glucose in the blood at an optimal level is associated with increased glycogen breakdown in hepatonites under the influence of the sympathetic nervous system, adrenaline, and glucagon. In hepatocytes, fat is broken down to form fatty acids. Short-chain fatty acids are converted here into higher fatty acids.

The liver acts as a depot for proteins, carbohydrates, fats, microelements, vitamins A, D1, D2, K, C, PP.

The liver performs a barrier (detoxification) function, neutralizing toxic substances entering the blood from the intestine (indole, phenol, skatole), foreign substances that do not participate in either plastic or energy processes of the body (xenobiotics), due to oxidation, reduction, hydrolysis reactions, as well as reactions of connection with glucuronic, sulfuric acids, glinin, glutamine (conjugation reactions). As is known, during the deamination of amino acids, nucleotides, and other intermediate products of protein metabolism in the liver, ammonia is formed, which is a highly toxic compound. Ammonia detoxification is carried out during the synthesis of urea, which is subsequently excreted by the kidneys.

Physiological activity of the liver is interconnected with the metabolism of hormones - protein-peptide, steroid, amino acid derivatives. Protein-peptide hormones are inactivated in the liver by proteinases, steroid hormones - by hydroxylases, catecholamines (adrenaline, noradrenaline, dopamine) are deaminated with the participation of monoamine oxidase.

The liver functions as a blood depot, participates in the destruction of red blood cells, biochemical transformations of heme with the formation of bile pigments, the liver participates in the body's immune reactions.

To summarize the above, the functions of the liver can be represented as follows.

• The nutritional function is the receipt, processing and accumulation of nutrients (amino acids, fatty acids, carbohydrates, cholesterol and vitamins) absorbed in the digestive tract, and the release of metabolites.
• Synthesis of substances - production of plasma proteins (albumins, blood clotting factors, transport proteins), synthesis of binding proteins that modulate the concentration of ions and drugs in the blood.
• Immunological function - participation in the process of transport of immunoglobulins, clearance of antigens in Kupffer cells.
• Hematological function - synthesis and secretion of coagulation factors, clearance of activated coagulation factors.
• Detoxifying function: the liver is the main site of metabolic transformations of endogenous and exogenous substances.
• Excretory function - metabolism of bile acids (synthesis of bile acids from cholesterol, secretion of bile acids into the intestine, as a result of which their concentration is regulated and effective emulsification and absorption of dietary fats are ensured).
• The endocrine function of the liver is the catabolism of a number of hormones (including thyroid and steroid hormones), and insulin metabolism.