Liver

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Liver "The main chemical laboratory of the body" - this is how scientists called the liver in the last century. Is there no exaggeration in this characterization? No. Truly miraculous transformations take place in the liver, and these transformations play such an important role in the life of the organism that it cannot exist without them.

STRUCTURE OF THE LIVER

The human liver weighs one and a half to two kilograms. It is the largest gland in our body. In the abdominal cavity, it occupies the right and part of the left hypochondrium. The liver is dense to the touch, but very elastic: adjacent organs leave well-visible marks on it. Even external causes, such as mechanical pressure, can change the shape of the liver.

The entire liver consists of many prismatic lobules ranging in size from one to two and a half millimeters. Each individual lobule contains all the structural elements of the whole organ and is like a liver in miniature. It is interesting that the lobules in the liver of a mouse differ from the hepatic lobules of an elephant mainly in number, but their structure is approximately the same. Under the microscope, it can be seen that a vein passes in the center of the lobule, and from it there are crossbeams with radii, consisting of two rows of cells. The bile produced by the cells goes out into the gap between them - this is the so-called bile capillary. Merging, the capillaries form larger passages. They connect to the bile duct, which gives off a lateral branch to the gallbladder located on the lower surface of the liver. The common bile duct flows into the duodenum. In this way, bile enters the intestines and participates in digestion.

Bile is produced by the liver continuously, but it enters the intestines only as needed. At certain times, when the intestines are empty, the bile duct closes.

The circulatory system of the liver is very peculiar. Blood flows to it not only through the hepatic artery from the aorta, but also through the portal vein, which collects venous blood from the abdominal organs. Arteries and veins are densely entwined with liver cells. Close contact of the blood and bile capillaries, as well as the fact that blood flows more slowly in the liver than in other organs, contribute to a more complete exchange of substances between blood and liver cells. The hepatic veins gradually connect and flow into a large collector - the inferior vena cava, into which all the blood that has passed through the liver is poured.
The external structure of the liver was already known in ancient times. The study of the internal structure of this organ is associated with the discovery of the microscope. Already in 1666, the Italian anatomist Malpighi described the structure of the hepatic lobules. However, the role of the liver in humans and animals remained unclear for a long time.

Liver BILD AND DIGESTION

For many years, the formation of bile was considered the main function of the liver. But the scientists had a very poor idea of why, for what purpose, this greenish-yellow liquid, very bitter in taste, was released. And only in the last 100 years, it has been possible, with the help of complex and ingenious experiments on animals, to unravel the diverse and (multifaceted function of the liver.

Already in the middle of the last century, scientists established that bile promotes the digestion of fats in the body. This was explained in detail by the great Russian physiologist I.P. Pavlov. To the abdominal wall of the animal, he sutured a piece of the intestinal mucosa with the bile duct flowing into it. The bile drained into a substituted test tube. It turned out that different foods cause unequal separation of bile into the intestines. Most of the bile is secreted into fats, the least - into carbohydrates. It was found that the cessation of bile secretion causes complete indigestion and changes the general condition of the experimental animals.Bile enhances the digestive effect of pancreatic and intestinal juices, stimulates bowel movements, promotes the separation of pancreatic juice.

The role of bile is especially important in the digestion of fats. Bile emulsifies fats, that is, breaks them down into tiny particles. This significantly increases the contact surface of fats with digesting juices. Finally, under the influence of bile (fat breakdown products are converted into highly soluble compounds and are easily absorbed into the blood and lymph.

I.P. Pavlov's research was supplemented by his students, especially I.P. Razenkov. They obtained valuable data by observing patients in whom, in connection with one or another disease, bile ducts were brought out. It turned out that bile plays the same role in the human body as in animals.

Naturally, a violation of the formation and excretion of bile causes serious changes in the vital activity of the body. And yet, the human body can adapt to existence and with a disorder of bile secretion. Volyns, in which the bile duct is blocked by a tumor or blocked by a gallstone, carry the disease for a long time / although bile does not enter the intestines at all. Naturally, a fat-free diet will greatly alleviate the disease. At the same time, acute lesions of the liver tissue caused by certain infectious diseases or poisoning can have a detrimental effect on the body. This means that the role of the liver is not limited to the formation and secretion of bile.

THE IMPORTANCE OF THE LIVER IN THE BODY

At the end of the last century, the surgeon N. N. Ekk set up a number of experiments. He created an artificial circulation in a dog, connecting the portal and inferior vena cava. As a result, blood from the abdominal organs began to enter the general bloodstream, bypassing the liver. Subsequently, this operation was repeated and improved by I.P. Pavlov and his collaborators. It turned out that after the imposition of such an anastomosis, the animal could only live for a few days. If the liver is removed from the dog, then it dies very quickly. Thus, * the assumption was confirmed that the main role of the liver is not in bile formation, but in some more complex and important processes. What are these processes?

The very location of the liver in the abdominal cavity, on the path between the intestines, where food is digested and absorbed, and the rest of the body sheds some light on its function. It is no accident that all the blood flowing from the abdominal organs flows into a powerful venous collector - the portal vein. This blood, as you know, carries nutrients that are broken down during digestion, and passes through the liver before entering the general circulation. What happens in the liver with the blood flowing from the abdominal organs?

Liver Let us recall that “various substances enter the body from the external environment, some of which are spent for energy purposes, and some of them are used to build new cells and tissues and to replace obsolete and decrepit ones. Substances that are unnecessary and harmful to the body are excreted into the external environment. The more perfect the organism, the more complex and diverse its relationship with the environment. In order for a highly developed organism to exist normally, the composition of its internal environment - blood and tissue fluid filling the intercellular spaces - must maintain a certain constancy. If this constancy changes, the normal functions of organs and tissues are also disrupted.

But how to keep the composition of blood and tissue fluid unchanged if the foodstuffs entering the body differ sharply in their structure from those substances that are part of the organs and tissues of the animal? Once in the general bloodstream, even after being digested in the digestive tract, these products drastically change the composition of the blood and “can cause serious diseases of the animal.Obviously, in the body in the process of evolution, special adaptations should have been developed for the chemical processing of products received from the outside into substances characteristic of their structure for a given (animal. Experiments with removing the liver or turning it off from the venous blood flow of the abdominal cavity clearly showed that the liver is one of these protective devices, a kind of barrier that lies between the gastrointestinal tract and the general circulation.

WONDERFUL TRANSFORMATIONS

Even at the beginning of the last century, it was known that by examining the composition of the blood flowing into and out of an organ, one can judge about the metabolic processes taking place in the organ itself. If, for example, the blood brings more sugar to the organ than it takes away, then the cells of the organ have retained some of the sugar. The same applies to “proteins, fats and other substances necessary for life.

But how to investigate the metabolism in the liver if it is hidden deep in the abdominal cavity and supplying it

blood vessels covered with skin, subcutaneous tissue, muscles, peritoneum, omentum? In the middle of the last century, the famous French scientist Claude Bernard studied the activity of the liver by cutting it out of the body. This allowed him to identify a number of very interesting patterns. But this method, of course, could not replace the study of biochemical processes “occurring in natural conditions in the liver of a living organism.

After many years of hard and painstaking work, the Soviet scientist E.S. London developed a simple way to study the role of the liver in metabolism. He sutured various organs, including the liver, to the Avens, thin tubes made of stainless metals, through which blood could be easily sucked with a long needle. This method made it possible to study the host of the liver in the metabolism of carbohydrates, fats, proteins and other substances. Subsequently, E.S. London introduced into the practice of a physiological experiment such a tube, through which it was possible to cut out small pieces of organ tissue to study their chemical composition.

All these experimental studies carried out on animals, as well as observations on sick people, have shown that the liver is directly or indirectly involved in all metabolic processes in the body.

First of all, the researchers paid attention to the participation of the liver in carbohydrate metabolism. Carbohydrates are essential for the life of the body. They are found mainly in plant foods. From bread potatoes, various cereals, the human body assimilates the main carbohydrate - starch... In the process of digestion, starch is broken down to a simple sugar - glucose, and it, passing through the mucous membrane of the intestinal wall, enters the bloodstream and through the portal vein enters the liver. Comparing the content of glucose in the blood flowing to and from the liver, scientists have found that part of the glucose is retained by the liver cells, and the rest passes through the liver and is carried by the blood throughout the body. Glucose remaining in the liver is converted into a complex carbohydrate compound - glycogen, which is called "animal starch" due to its similarity to starch. Glycogen is retained in liver cells in the form of insoluble shiny microscopic lumps. But the liver retains glucose only when the content of glucose entering the bloodstream from the intestine exceeds a tenth of a percent. Otherwise, the concentration of glucose in the blood flowing through the liver does not change.

Glucose - the fuel of the animal organism. No organ can function without it. Some organs use it directly as a source of energy. Then it burns down to carbon dioxide and water. This happens, for example, in the brain. Other organs first convert glucose into glycogen, and the latter is used as an energy source. This applies mainly to the muscles. In an active state, they consume 3-4 times more sugar than at rest.How is sugar loss during work covered?

The concentration of sugar in the blood is a fairly constant value, a decrease in blood sugar to half the norm causes convulsions and has a detrimental effect on the body. Can you imagine that the loss of blood sugar is continuously replenished with glucose coming from the intestines? Of course not. After all, there are long breaks between meals, and even with prolonged fasting, the blood sugar content still remains at the same level.

The liver plays a major role in maintaining a constant blood sugar level, that is, in an even supply of fuel to all organs. If the body receives a lot of sugar, the excess is deposited in the liver as glycogen. It is like a reserve fuel storage. As soon as organs and tissues begin to feel the need for sugar, liver glycogen is converted into glucose, which enters the blood. Glycogen stores in the liver reach 150 grams. With fasting and muscle work, these reserves are reduced. Studies show that blood flowing from the liver of starving animals contains more sugar than flowing to it.

However, the calculation suggests that the reserves of glycogen in the liver can only be enough for two to three hours of intensive work. Consequently, the body has some other ability to replenish sugar stores, and it gets it not only from carbohydrates from food, but also from some other sources. Really! this assumption was justified. It turned out that lactic acid, into which glycogen passes during muscle work, is transported with the blood flow to the liver and here glycogen is again restored from it through complex chemical transformations. Moreover, the liver is capable of producing sugar not only from carbohydrates, but also from fats and proteins. With the help of these complex transformations, the fancy liver maintains a certain sugar level in the jury and thereby maintains and regulates the activity of almost all organs of our body.

The liver is equally important in protein metabolism. Proteins are the main building blocks of the body. During life, most of the cells in our body have time to completely change more than once. And since the basic building blocks of organs are built from proteins, proteins are essential to sustain life.

In the digestive canal, proteins from food are broken down into simple particles - amino acids. In the tissues of the body, amino acids are re-combined into protein molecules. But this protein is different from that which is obtained by the body from food. It is in the liver that the most complex transformations of amino acids take place, and not only the substances that come from the intestines are processed, but also the products of protein breakdown of tissues and organs of the body that have entered the bloodstream. Reserve proteins accumulate in the liver in the same way as glycogen, and are consumed when the body needs them more. Those proteins that are not used to build tissues and are not stored as a reserve are also processed by the liver.

After going through a number of diverse biochemical reactions, such proteins are converted into glucose and used as a source of energy. At the same time, ammonia is split off from amino acids, which is toxic to the body in large quantities. The liver neutralizes it: it turns into a harmless compound urea, which is excreted from the body by the kidneys. Under the influence of putrefactive bacteria that inhabit the intestines, some amino acids form toxic substances. They are also retained and rendered harmless by the liver.

The role of the liver is also great in fat metabolism. It is not limited to secreting bile for the digestion of fat in the intestines. If necessary, to cover the energy costs of the body, the liver can convert fats into sugar. The body always has reserves of fat, which, if appropriate, can be mobilized.

In the liver itself, fat stores are also created, and these reserve fats are in such a mobile chemical state that they can easily pass into other compounds. Finally, cholesterol is formed in the liver, a complex fat-like compound that plays an important role in the life of the body.

The liver is also of great importance for the exchange of vitamins in the body. It is formed and deposited vitamin A... The liver also contains vitamins B, C, E, K, D.

The liver takes a certain part in water-salt metabolism. Swelling, it can absorb and accumulate excess fluid and prevent blood from thinning.

The liver has the ability to collect blood stores. The hepatic veins narrow and over time more blood flows to the liver than flows from it. When needed, reserve blood is released into the general circulation.

It was already mentioned above about the ability of the liver to retain and neutralize poisonous decay products, which are inevitably produced in the process of metabolism. But the liver plays the role of a barrier not only in relation to harmful decomposition products, but also to all toxic substances that have entered the body. Poisonous megaliths and metalloids (mercury, arsenic, lead, copper and others) are retained by the liver and converted into compounds that are harmless to the body. In the liver, there is also a delay and neutralization of pathogenic microbes and toxic products released by them.

Violation of the barrier function of the liver always has a very heavy effect on the vital activity of the whole organism.

Liver CIRCLE OF INTERACTION

The functions of the liver are diverse. Its activity is influenced by other organs of our body, and most importantly, it is under the constant and unremitting control of the nervous system. Under the microscope, you can see that nerve fibers densely entwine each hepatic lobule. But the nervous system has more than a direct effect on the liver. It coordinates the work of other organs that affect the liver. This applies primarily to the organs of internal secretion.

Back in the middle of the 19th century, Claude Bernard made a number of interesting experiments. It turned out that an injection into one of the parts of the rabbit's brain causes an intensive conversion of liver glycogen into sugar in neto, and as a result, the blood sugar level rises. Scientists have figured out the reason for these transformations. It turns out that "sugar prick", as it was later called, causes the conversion of glycogen to sugar in two ways. Firstly, by direct action on liver cells through nerve fibers, and secondly, by nervous excitation of special endocrine glands - the adrenal glands, which in this case begin to intensively release adrenaline into the blood. Adrenaline, entering the liver with blood, in turn promotes the conversion of glycogen into sugar. Insulin, a hormone from the pancreas, as opposed to adrenaline, converts blood sugar into liver glycogen.

The release of insulin and adrenaline is regulated by the central nervous system. It has been established, for example, that emotional arousal is usually accompanied by an increased release of adrenaline into the blood and an increase in blood sugar levels.

It can be considered proven that the central nervous system regulates the liver - directly or through other systems of the body. It sets the intensity and direction of liver metabolic processes in accordance with the needs of the body at the moment. In turn, biochemical processes in liver cells irritate sensitive nerve fibers and thereby affect the state of the nervous system.

This closes the circle of mutual influences, mutual connections in the body. That is why the activity of the liver, like that of any other organ, cannot be considered independently of the general state of the organism.