Water exchange functions in the body. Water and mineral metabolism. Diseases caused by lack of water in the body

Water plays an important role in the physiological processes of the body. It makes up 65-70% of body weight (40-50 l). The overall balance of water in the body is determined, on the one hand, by the intake of water with food (2-3 l) and the formation of endogenous (internal) water (200-300 ml), on the other hand, by its excretion through the kidneys (600-1200 ml) and from feces (50-200 ml).

A person's need for water under normal conditions is 2.5 liters. In high mountain conditions, water exchange changes dramatically. The release of water through the skin and lungs increases significantly, the body “dries out” at high altitudes, and urine output decreases. The body's need for fluid depends on the altitude, dry air, load, and training of the climber. During the period of training and preparatory ascents, it ranges from 2 to 3 liters per day. When climbing at high altitudes, you must adhere to this norm, and, if possible, increase it to 3.5-4.5 liters, which will fully meet the physiological needs of the body. During the Everest expedition (1953), fluid consumption was in the range of 2.8-3.9 liters per person.

Water metabolism is closely related to mineral metabolism, especially to the metabolism of sodium chloride and potassium chloride. Maintaining water-salt homeostasis (balance) also affects the activity of other functional systems of the body - nervous, cardiovascular, respiratory and others. The cerebral cortex, which contains the largest amount of water, suffers more than others from its lack. At the same time, water and drinking insufficiency is also added to hypoxia.

There are three parts in maintaining water-salt balance: the intake of water and salts into the body, their redistribution between intracellular and extracellular systems, and their release into the external environment. Sodium ions play a leading role in maintaining homeostasis, so it is imperative to take salt with you when climbing; the body should receive up to 15-20 g of salt daily. A lack of potassium leads to muscle weakness, disruption of the cardiovascular system, and decreased mental and mental activity.

Water exchange

The structure and dimensions of the fluid sectors of the body, that is, spaces filled with fluid and separated by cell membranes, have now been quite well studied. The total volume of body fluids, which in mammals accounts for approximately 60% of body weight, is distributed between two large sectors: intracellular (40% of body weight) and extracellular (20% of body weight). The extracellular sector includes the volume of fluid located in the interstitial (intercellular) space and fluid circulating in the vascular bed. A small volume is also made up of the so-called transcellular fluid, located in regional cavities (cerebrospinal, intraocular, intraarticular, pleural, etc.). Extracellular and intracellular fluids differ significantly in composition and concentration of individual components, but the total total concentration of osmotically active substances is approximately the same (Table 1). The movement of water from one sector to another occurs even with small deviations in the total osmotic concentration. Since most dissolved substances and water molecules pass quite easily through the capillary epithelium, rapid mixing of all components (except protein) occurs between the blood plasma and the interstitial fluid. Many factors, such as intake, loss or limitation of water intake, increased salt intake or, conversely, its deficiency, shift in metabolic rate, etc., can change the volume and composition of body fluids. The deviation of these parameters from a certain normal level includes mechanisms that correct disturbances in water-salt homeostasis.

General scheme of water-salt balance

The system for regulating water-salt balance has two compensating components: 1) the digestive tract, which can approximately correct disturbances in the water-salt balance due to thirst and salt appetite; 2) kidneys, capable of providing adequate retention or excretion of water and salts to maintain balance. In Fig. Figure 1 shows a diagram of the main routes of entry and release of water and salts. The main channel for the entry of water and salts into the blood plasma and other body fluids is the gastrointestinal tract. Per day consumption is approximately 2.5 liters of water and 7 g of sodium chloride. To this you can add 0.3 liters of metabolic water released as a result of oxidative water.

Table 1

Concentration of electrolytes and organic components in body fluids in humans (average data from various literature sources)

It is not very easy to imagine that a person is approximately 65% ​​water. With age, the water content in the human body decreases. The embryo consists of 97% water, the body of a newborn contains 75%, and an adult contains about 60%.

In a healthy adult body, a state of water equilibrium or water balance is observed. It lies in the fact that the amount of water consumed by a person is equal to the amount of water removed from the body. Water metabolism is an important component of the general metabolism of living organisms, including humans. Water metabolism includes the processes of absorption of water that enters the stomach when drinking and with food, its distribution in the body, excretion through the kidneys, urinary tract, lungs, skin and intestines. It should be noted that water is also formed in the body due to the oxidation of fats, carbohydrates and proteins taken with food. This type of water is called metabolic water. The word metabolism comes from Greek, which means change, transformation. In medicine and biological science, metabolism refers to the processes of transformation of substances and energy that underlie the life of organisms. Proteins, fats and carbohydrates are oxidized in the body to form water H 2 O and carbon dioxide (carbon dioxide) CO 2. The oxidation of 100 g of fat produces 107 g of water, and the oxidation of 100 g of carbohydrates produces 55.5 g of water. Some organisms make do with only metabolic water and do not consume it from the outside. An example is carpet moths. In natural conditions, jerboas, which are found in Europe and Asia, and the American kangaroo rat do not need water. Many people know that in an exceptionally hot and dry climate, the camel has a phenomenal ability to go without food and water for a long time. For example, with a mass of 450 kg, during an eight-day trek through the desert, a camel can lose 100 kg in mass, and then restore it without consequences for the body. It has been established that his body uses water contained in the fluids of tissues and ligaments, and not blood, as happens with a person. In addition, the camel's humps contain fat, which serves as both a food store and a source of metabolic water.

The total volume of water consumed by a person per day when drinking and with food is 2...2.5 liters. Thanks to the water balance, the same amount of water is removed from the body. About 50...60% of water is removed through the kidneys and urinary tract. When the human body loses 6...8% of moisture above the normal norm, the body temperature rises, the skin turns red, the heartbeat and breathing quicken, muscle weakness and dizziness appear, and a headache begins. A loss of 10% of water can lead to irreversible changes in the body, and a loss of 15...20% leads to death, since the blood becomes so thick that the heart cannot cope with pumping it. The heart has to pump about 10,000 liters of blood per day. A person can live without food for about a month, but without water - only a few days. The body's reaction to a lack of water is thirst. In this case, the feeling of thirst is explained by irritation of the mucous membrane of the mouth and pharynx due to a large decrease in humidity. There is another point of view on the mechanism of formation of this sensation. In accordance with it, a signal about a decrease in the concentration of water in the blood is sent to the cells of the cerebral cortex by the nerve centers embedded in the blood vessels.

Water metabolism in the human body is regulated by the central nervous system and hormones. Dysfunction of these regulatory systems causes disruption of water metabolism, which can lead to body edema. Of course, different tissues of the human body contain different amounts of water. The richest tissue in water is the vitreous body of the eye, containing 99%. The poorest is tooth enamel. It contains only 0.2% water. There is a lot of water in the brain matter.

Macronutrients

Macroelements include K, Na, Ca, Cl. For example, with a person weighing 70 kg, it contains (in grams): calcium - 1700, potassium - 250, sodium - 70.

The high content of calcium in the human body is explained by the fact that it is contained in significant quantities in the bones in the form of calcium hydroxyphosphate - Ca 10 (PO 4) 6 (OH) 2 and its daily intake for an adult is 800-1200 mg.

The concentration of calcium ions in the blood plasma is maintained very precisely at the level of 9-11 mg% and in a healthy person rarely fluctuates more than 0.5 mg% above the normal level, being one of the most precisely regulated factors of the internal environment. The narrow boundaries within which the calcium content in the blood fluctuates are due to the interaction of two hormones - parathyroid hormone and thyrocalcitonin. A fall in the level of calcium in the blood leads to increased internal secretion of the parathyroid glands, which is accompanied by an increase in the flow of calcium into the blood from its bone depots. On the contrary, an increase in the content of this electrolyte in the blood inhibits the release of parathyroid hormone and enhances the formation of thyrocalcitonin from the parafollicular cells of the thyroid gland, resulting in a decrease in the amount of calcium in the blood. In humans, with insufficient intrasecretory function of the parathyroid glands, hypoparateriosis develops with a drop in the level of calcium in the blood. This causes a sharp increase in the excitability of the central nervous system, which is accompanied by seizures and can lead to death. Hyperfunction of the parathyroid glands causes an increase in calcium in the blood and a decrease in inorganic phosphate, which is accompanied by the destruction of bone tissue (osteoporosis), muscle weakness and pain in the limbs.

SODIUM and POTASSIUM

The vital elements sodium and potassium function in pairs. It has been reliably established that the rate of diffusion of Na and K ions through the membrane at rest is small, the difference in their concentrations outside the cell and inside should eventually level out if there were no special mechanism in the cell that ensures active excretion (“pumping out”) from protoplasm of sodium ions penetrating into it and the introduction (“pumping”) of potassium ions. This mechanism is called sodium - potassium pump.

In order for ionic asymmetry to be maintained, the sodium-potassium pump must pump sodium ions out of the cell against the concentration gradient and pump potassium ions into it and, therefore, do a certain amount of work.

The direct source of energy for the pump is the breakdown of energy-rich phosphorus compounds - ATP, which occurs under the influence of the enzyme - adenosine triphosphatase, localized in the membrane and activated by sodium and potassium ions. Inhibition of the activity of this enzyme, caused by certain substances, leads to disruption of the pump. It is interesting that as the body ages, the concentration gradient of potassium and sodium ions at the cell boundary decreases, and when death occurs, it levels out.

Microelements

These include the above-mentioned series of 22 chemical elements that are necessarily present in the human body. Note that most of them are metals, and the main metal is iron.

Despite the fact that the iron content in a person weighing 70 kg does not exceed 5 g and the daily intake is 10 - 15 mg, it plays a special role in the life of the body.

Iron occupies a very special place, since it is not affected by the secretory system. Iron concentration is regulated solely by absorption, not excretion. In the adult body, about 65% of all iron is contained in hemoglobin and myoglobin, most of the remainder is stored in special proteins (ferritin and hemosiderin), and only a very small part is found in various enzymes and transport systems.

Hemoglobin and myoglobin

Hemoglobin plays an important role in the body as an oxygen carrier and takes part in the transport of carbon dioxide. The total hemoglobin content is 700g, and the blood of adults contains on average about 14 - 15%.

Hemoglobin is a complex chemical compound (molecular weight 68,800). It consists of the protein globin and four heme molecules. The heme molecule, containing an iron atom, has the ability to attach and donate an oxygen molecule. In this case, the valency of the iron to which oxygen is added does not change, i.e., the iron remains divalent.

Oxyhemoglobin is slightly different in color from hemoglobin, so arterial blood containing oxyhemoglobin is bright scarlet. Moreover, the brighter it became, the more completely it was saturated with oxygen. Venous blood, containing a large amount of reduced hemoglobin, has a dark cherry color.

Methemoglobin is an oxidative hemoglobin, during the formation of which the valency of iron changes: divalent iron, which is part of the hemoglobin molecule, is converted into trivalent iron. If there is a large accumulation of methemoglobin in the body, the delivery of oxygen to the tissues becomes impossible and death from suffocation occurs.

Carboxyhemoglobin is a compound of hemoglobin with carbon monoxide. This connection is approximately 150 - 300 times stronger than the connection of hemoglobin with oxygen. Therefore, the admixture of even 0.1% carbon monoxide in the inhaled air leads to the fact that 80% of hemoglobin is associated with carbon monoxide and does not attach oxygen, which is life-threatening.

Myoglobin. Myoglobin is found in skeletal and cardiac muscle. It is capable of binding up to 14% of the total amount of oxygen in the body. This property plays an important role in supplying oxygen to working muscles. If, when a muscle contracts, its blood capillaries are compressed and the blood flow in some areas of the muscle stops, the supply of oxygen to the muscle fibers is maintained for some time.

Transferrin

Transferrin is a class of iron-binding molecules. The most studied - serum transferrin - is a transport protein that transfers iron from hemoglobin fragments of the spleen and liver to the bone marrow, where hemoglobin is synthesized again in special areas. All serum transferrin, binding only 4 mg of iron at a time, transfers about 40 mg of iron daily to the bone marrow - very significant evidence of its effectiveness as a transport protein. Patients with genetically determined disorders of transferrin synthesis suffer from iron deficiency anemia, immune system disorders and intoxication from excess iron!

Transferrin is a glycoprotein with a molecular weight of about 80,000. It consists of one polypeptide chain, folded so that it forms two compact sections, each of which is capable of binding one iron (III) ion. True, the binding of iron is possible only with the binding of an anion. In the absence of a suitable anion, the iron cation does not bind to transferrin. In most cases, carbonate is used for this in nature, although other anions, such as oxalate, malonate, and citrate, are also capable of activating the metal binding site.

The high stability of the iron complex with transferrin makes it an excellent carrier, but it also poses the problem of releasing iron from the complex. Many of the good chelating agents are of little use as mediators of iron release. The most effective of them was pyrophosphate. Given the essential role of iron binding to transferrin, it would be logical to propose that anion scavenging must underlie any iron release mechanism, but no correlation has been found between the ability to displace carbonate in the transferrin complex and their effectiveness as a mediator of iron release. In the transport system of microbes, the release of iron ions by the carrier is caused by their reduction to Fe (II), but, as has been reliably established, iron is released from transferrin in the form of Fe (III).

Iron intake occurs during the catalytic oxidation of Fe (II) to Fe (III) by appoferritin, and release occurs during the reduction of Fe (II) with reduced flavins. In most cells, ferritin synthesis is significantly accelerated in the presence of iron; in rat liver cells, the synthesis of subunits takes place in 2 - 3 minutes.

A lack of copper in the body leads to the destruction of blood vessels, pathological bone growth, and defects in connective tissues. In addition, copper deficiency is believed to be one of the causes of cancer. In some cases, doctors associate lung cancer in older people with an age-related decrease in copper in the body. Much is known about copper transport in the body. A significant portion of copper is in the form of ceruloplasmin. Copper content in the body varies from 100 to 150 mg with the highest concentration in the brain stem. High consumption of copper leads to deficiency and is unfavorable for humans. A progressive brain disease in children (Menkes syndrome) is associated with copper deficiency, as the disease lacks a copper-containing enzyme. Some improvements in the condition of these patients were obtained with the introduction of copper. Excessive amounts of copper in the body are also unfavorable and lead to the development of serious diseases. In Wilson's disease, the copper content increases almost 100 times compared to normal. Copper is found in many tissues, but it is especially abundant in the liver, kidneys and brain. It can be seen on the cornea in the form of brown or green circles. It has now been established that initially excess copper concentrations occur in the liver, then in the nervous system, and the manifestation of disorders of these organs occurs in the same order. Symptoms of Wilson's disease include cirrhosis of the liver, loss of coordination, severe tremors, and progressive tooth decay. The severity of symptoms depends on the amount of copper content. Reduction of clinical symptoms can be achieved by using chelating agents that remove excess copper reserves. The very fact that symptoms disappear after such therapy means that brain destruction is more a biological process than a structural one.

Despite the genetically dependent nature of the disease, copper deposition in tissues is not always observed. Copper is deposited in certain copper proteins in the liver; in Wilson's disease, the synthesis of apoceruloplasmin is disrupted in such a way that copper cannot bind to these proteins and begins to be deposited in other places. It is clear that this cannot serve as the only explanation, since in a number of patients the level of ceruloplasmin is slightly reduced. In addition, copper is found in large quantities in the liver of newborns, with 2% of the total copper bound to protein. After three months, the concentration decreases to normal levels, from which time the liver is able to synthesize the protein ciruloplasmin. There is another point of view on Wilson's disease: the structure of the metalloteonin protein in Wilson's disease is disrupted, and this leads to increased binding of copper ions, which in turn leads to disruption of copper reserves and transport in the body. Increased copper binding by metallothionein has been demonstrated in patients with Wilson's disease.

When treating Wilson's disease, eat foods low in copper and use chelating agents, especially penisillamine.

In many other diseases, an increase in serum copper is observed: for example, in infectious hepatitis, an increase in serum copper is observed 3 times compared to the norm - 350 µg/100 ml. this is due to the accumulation of ceruloplasmin. An increase in copper in the blood occurs in diseases such as leukemia, lymphoma, rheumatoid arthritis, cirrhosis, and nephritis. High copper levels can be associated with a variety of events, and the detection of high serum copper concentrations is only of diagnostic value when considered in conjunction with other studies. An analysis of the concentration of copper ions must be carried out to assess the effectiveness of treatment, since the level of copper is directly proportional to the severity of the disease. This situation is true for hepatitis and malignant diseases.

Zinc is of great importance for the human body; on average, the body contains about 3g, and the daily intake is 15mg. Zinc deficiency in humans is expressed in loss of appetite, disturbances in the skeleton and hair growth, skin damage, and delayed puberty. In several cases, zinc deficiency has led to severe disturbances in the sensory apparatus in people, expressed in perversion of taste and smell. In these patients, symptoms of anorexia and impaired physiological toxicity can be relieved by dietary zinc supplementation. Zinc plays an important role in wound healing. With zinc deficiency, this process is slow due to a decrease in protein and collagen synthesis. It follows that to improve wound healing, zinc should be added to the diet of patients with a deficiency of the element.

We paid great attention to the role of metals. However, it must be taken into account that some non-metals are also absolutely necessary for the functioning of the body.

Silicon is also an essential trace element. This has been confirmed by careful studies of rat nutrition using different diets. Rats gained significant weight when sodium metasilicate (Na 2 (SiO) 3 . 9H 2 O) was added to their diet (50 mg per 100 g). Chickens and rats need silicon for growth and skeletal development. A lack of silicon leads to disruption of the structure of bones and connective tissue. As it turned out, silicon is present in those areas of the bone where active calcification occurs, for example, in bone-forming cells, osteoblasts. With age, the concentration of silicon in cells decreases.

Little is known about the processes in which silicon is involved in living systems. There it is in the form of silicic acid and probably participates in carbon cross-linking reactions. In humans, the richest source of silicon turned out to be hyaluronic acid from the umbilical cord. It contains 1.53 mg of free and 0.36 mg of bound silicon per gram.

Selenium deficiency causes muscle cell death and leads to muscle failure, in particular heart failure. Biochemical study of these conditions led to the discovery of the enzyme glutathione peroxidase, which destroys peroxides. A lack of selenium leads to a decrease in the concentration of this enzyme, which in turn causes lipid oxidation. Selenium's ability to protect against mercury poisoning is well known. Much less well known is the fact that there is a correlation between high selenium in the diet and low cancer mortality. Selenium is included in the human diet in the amount of 55 - 110 mg per year, and the concentration of selenium in the blood is 0.09 - 0.29 µg/cm. When taken orally, selenium is concentrated in the liver and kidneys. Another example of the protective effect of selenium against intoxication with light metals is its ability to protect against poisoning by cadmium compounds. It turned out that, as in the case of mercury, selenium forces these toxic ions to bind to ionic active centers, those that are not affected by their toxic effect.

Chlorine and bromine

Halogen anions differ from all others in that they are simple, rather than oxo, anions. Chlorine is extremely widespread, it is able to pass through the membrane and plays an important role in maintaining osmotic balance. Chlorine is present in the form of hydrochloric acid in gastric juice. The concentration of hydrochloric acid in human gastric juice is 0.4-0.5%.

There are some doubts about the role of bromine as a trace element, although its sedative effect is reliably known.

Fluoride is absolutely necessary for normal growth, and its deficiency leads to anemia. Much attention has been paid to the metabolism of fluoride in connection with the problem of dental caries, since fluoride protects teeth from caries.

Dental caries has been studied in sufficient detail. It begins with the formation of a stain on the surface of the tooth. Acids produced by bacteria dissolve tooth enamel under the stain, but, oddly enough, not from its surface. Often the top surface remains intact until the areas underneath are completely destroyed. It is assumed that at this stage, fluoride ion may facilitate the formation of apatite. In this way, the damage that has begun is reminelized.

Fluoride is used to prevent destruction of tooth enamel. You can add fluoride to toothpaste or directly treat your teeth with it. The fluoride concentration required to prevent caries in drinking water is about 1 mg/l, but the level of consumption depends not only on this. The use of high concentrations of fluoride (more than 8 mg/l) can adversely affect the delicate equilibrium processes of bone tissue formation. Excessive absorption of fluoride leads to fluorosis. Fluoride leads to thyroid dysfunction, growth inhibition and kidney damage. Long-term exposure to fluoride in the body leads to mineralization of the body. As a result, the bones are deformed, which can even grow together, and calcification of the ligaments occurs.

The main physiological role of iodine is its participation in the metabolism of the thyroid gland and its inherent hormones. The ability of the thyroid gland to accumulate iodine is also inherent in the salivary and mammary glands. And also to some other organs. Currently, however, it is believed that iodine plays a leading role only in the life of the thyroid gland.

Lack of iodine leads to characteristic symptoms: weakness, yellowing of the skin, feeling cold and dry. Treatment with thyroid hormones or iodine eliminates these symptoms. A lack of thyroid hormones can lead to an enlarged thyroid gland. In rare cases (a burden in the body of various compounds that interfere with the absorption of iodine, for example thiocyanate or the antithyroid agent goitrin, found in various types of cabbage), a goiter forms. Lack of iodine especially affects the health of children - they lag behind in physical and mental development. An iodine-deficient diet during pregnancy leads to the birth of hypothyroid children (cretins).

Excess thyroid hormones lead to exhaustion, nervousness, tremors, weight loss and excessive sweating. This is due to an increase in peroxidase activity and, consequently, an increase in iodination of thyroglobulins. Excess hormones can be a consequence of a thyroid tumor. During treatment, radioactive isotopes of iodine are used, which are easily absorbed by thyroid cells.

Inorganic compounds, making up only 6% of a person's total weight, are essential substances that ensure homeostasis of the body. All chemical elements are divided into macro-, micro- and ultramicro elements. Any change in the content of chemicals, either upward or downward, leads to metabolic disorders.

Among the numerous series of regulations characteristic of higher animals and humans, those that ensure the constancy of the mineral composition of the blood plasma work most accurately. Already in the prototypes of the animal world, at the very early stages of evolution, cells and all complex intracellular biochemical processes that ensure life adapted to a certain proportion of ions in the external environment. Biological evolution took place under the continuous influence of changes in inanimate nature. For some creatures, it consisted of a restructuring of cellular processes following a change in the salt composition of the aquatic environment. Others, which gave rise to a progressively developing branch of the animal world, developed special physiological mechanisms that make it possible to maintain the constancy of the composition of the intercellular fluid and blood plasma (the so-called internal environment of the body) and thus provide, in a changing external environment, optimal conditions for the functioning of all cells of the body, especially brain cells. Since the cell is separated from the extracellular fluid by a membrane, which is penetrated by protein structures - pores that are easily permeable to water, but not to most other components, then if there is a difference in the concentrations of substances, the water moves into a sector with a higher concentration of the solution according to the laws of osmosis. Any change in cell volume (swelling when water enters or shrinking when it is lost) will be accompanied by a disruption of biochemical intracellular processes.

The cells of the body are constantly in full swing: proteins, fats and carbohydrates are constantly synthesized. At the same time, complex organic compounds are broken down and energy is released.

The resulting breakdown products - urea, ammonia and carbon dioxide - must be removed from the body. And all these processes are possible only with the participation of water. Water is not only an important component of all cells, but also the basis of intercellular fluid, plasma, lymph and digestive juices.

The role of water in protein metabolism

Water plays a key role in protein synthesis. Enzymes of gastric, pancreatic and intestinal juices, which also contain water, break down the protein components of food into amino acids, which enter the blood and are carried into the cells of the body. And already in the cells the proteins necessary for the body are synthesized. Thus, thanks to the participation of water, organs and tissues receive the building material necessary for growth and development.

The role of water in carbohydrate metabolism

Carbohydrates are the main source of energy in the body. Enzymes from saliva, pancreatic and intestinal juices break down carbohydrates ingested from food into glucose, which is absorbed into the blood in the small intestine. When in excess, it is deposited in the liver as a strategic reserve of the body in the form of glycogen. Reverse conversion and delivery are also possible thanks to the aqueous medium, that is, blood.

The role of water in fat metabolism

The formation of fats in the body is also impossible without water. Food fats are broken down into glycerol and fatty acids by the action of enzymes in gastric, pancreatic and intestinal juices. They form fat in the small intestine. In the form of an emulsion, it is transported into the lymph, and with it into the general bloodstream. Excess fat is stored in the body or used as a source of energy.

Participation of water in thermoregulation

Water, influencing metabolism, produces energy in the body. It has a high heat capacity - 4200 J/(kg K). Therefore, it is a kind of temperature regulator in the human body. It also maintains body temperature in accordance with the ambient temperature.

Excretory function of water

Water is a medium for the safe removal of toxins and waste products (carbon dioxide, ammonia, uric acid, etc.). The body of a healthy adult can excrete about 3 liters of fluid per day: through the urinary tract, rectum, sweat glands and lungs. Therefore, to ensure normal metabolism, a person must replenish the amount of fluid expended every day. This is an average of 2.5-3 liters of water.

Water is needed

Lack of water in the body can lead to the development of serious diseases. Clean drinking or mineral water should predominate in the drinking ration.

You need to know: most of the liquids consumed by a person (tea, coffee, sweet carbonated drinks, alcohol, etc.) contain substances that have the opposite effect - they help remove water from the body’s cells, rather than saturate them with the necessary fluid.

Water forms the basis of all biological fluids: blood, lymph, cerebrospinal fluid, urine, digestive juices, intercellular fluid.

The animal body consists of 60-70% water, which is divided into intracellular and extracellular. The largest amount of water is contained inside cells. Extracellular fluid includes blood plasma, interstitial fluid and lymph. The basis of extracellular and intracellular water is free water. Water included in colloidal systems is called bound. Thanks to the action of enzymes, water is included in numerous biochemical reactions: hydrolysis, hydration, synthesis of all organic substances, and cellular respiration processes. Water serves as the medium in which all biochemical reactions of the body occur. Water is used in the body to form various secretions and is lost through sweat, feces, exhaled air vapor, and urine.

A healthy animal has water balance in its body. The kidneys, lungs, skin, gastrointestinal tract, and endocrine glands take part in water metabolism. The kidneys serve as the main organ for regulating water metabolism. In conditions of lack of water, they produce little urine, but it is highly concentrated. When there is excess water, the kidneys excrete large amounts of dilute urine. The ability of the kidneys to change the concentration of urine is impaired in severe kidney disease.

The lungs release water in the form of water vapor. This occurs as a result of the fact that the air in the alveoli at body temperature is saturated with water vapor. The amount of water excreted through the lungs depends on metabolism, respiratory rate and body temperature. With increased muscle activity, fever, and excitement, the volume of breathing increases and, accordingly, the amount of water excreted increases.

Through the skin, water loss occurs through evaporation and sweat. The evaporation of water by the skin depends on the difference in body temperature and the external environment. Sweat is the secretion of the sweat glands. Sweating occurs periodically and is associated with an increase in air temperature. The body's ability to secrete sweat of different compositions is an adaptive reaction. At high ambient temperatures, animals with insufficient acclimatization produce sweat, the composition of which approaches the composition of blood plasma.

A certain amount of water is formed in the body during the oxidation of certain substances. For example, when 100 g of fat is oxidized, 87 ml of water is formed. Horses consume an average of 40-50 liters of water per day, cattle - 40-90 liters, pigs - 10-20 liters.

The regulation of water-salt metabolism is carried out by the hypothalamus, located in the diencephalon. The hypothalamus contains the thirst center and special receptors. These structures are associated with osmoreceptors. Osmoreceptors are cells that are highly sensitive to changes in the osmotic pressure of the internal environment. Osmoreceptors are located in the hypothalamus, as well as in the blood vessels of the liver, kidneys, spleen, digestive tract, and in the sinocarotid reflexogenic zone. Some osmoreceptors belong to mechanoreceptors, since they respond to changes in cell volume when fluid enters or leaves it in the event of a change in the osmotic pressure of the environment. Other osmoreceptors are chemoreceptors and detect the concentration of specific ions. Among these receptors, specialized Na receptors, as well as calcium and magnesium receptors, are important. Osmoreceptors, perceiving changes in osmotic pressure, transmit information to the hypothalamus, which regulates the secretion of hormones by the pituitary gland.

Information about osmotic pressure enters the hypothalamus not only from osmoreceptors, but also from volume receptors - receptors that respond to changes in the volume of intravascular and intracellular fluid. These receptors are localized in the atria, right ventricle, and vena cava. Impulses from volume receptors enter the central nervous system via afferent fibers of the vagus nerve.

Osmotic pressure is the diffusion pressure that ensures the movement of solvent through a semipermeable membrane. Normally, in animals and humans it is 7.6 atm (7.6 10 5 Pa). Deviation of the value of this parameter from the norm is life-threatening. Therefore, reliable mechanisms for regulating osmotic pressure, the amount of salts and water have been formed in the body.

When the body is dehydrated, the concentration of osmotically active substances in the blood plasma increases, osmotic pressure increases, osmoreceptors are excited and the production of adrenocorticotropic hormone (ACTH) is inhibited, and the secretion of antidiuretic hormone increases. This hormone increases the reabsorption of water in the loop of Henle, inhibits the processes of reabsorption of salts, while simultaneously increasing filtration in the Malpighian glomeruli. This leads to the retention of water in the tissues, the removal of salts from the body and the normalization of the osmotic pressure of fluids.

With excess water content in the body (overhydration), the concentration of dissolved osmotically active substances in the blood decreases and its osmotic pressure drops. The formation of antidiuretic hormone (ADH) decreases, and ACTH, on the contrary, increases. Adrenocorticotropic hormone stimulates the function of the zona glomerulosa of the adrenal cortex, where mineralocorticoids are produced, as well as the zona fasciculata, which produces glucocorticoids.

Of the mineralocorticoids, the most active is aldosterone, and of the glucocorticoids, cortisone. These hormones narrow the lumen of the efferent vessels, inhibit the reabsorption of water and increase the reabsorption of salts.

Maintaining optimal blood osmotic pressure is associated with certain drinking behavior caused by thirst.

Thirst in animals occurs when the water content in the body decreases or when sodium concentration increases and is associated with irritation of many receptors. When drinking, water very quickly reduces thirst due to a decrease in the flow of impulses from the osmoreceptors of the gastrointestinal tract to the drinking center. Then the water is absorbed and enters the general bloodstream, the internal environment again becomes isotonic and true water saturation occurs.

Water exchange

Tissues and cells use two types of water: exogenous and endogenous. Exogenous water enters the body from the outside - with food and drink. In total, it makes up 6/7 of all the water necessary for the life of the body. 1/7 of the total mass of water is formed in animal tissues as the final product of the oxidation of nucleic acids, proteins, lipids, and carbohydrates. This endogenous water. It has been established that with complete oxidation

For 100 g of fat, the body receives 107.1 g of water, carbohydrates - 55.6 and proteins - 41.3 g of water. The endogenous pathway for the body to obtain water is of great importance for the inhabitants of arid deserts and steppes, and for animals that hibernate.

Water suction. A small amount of water is absorbed in the oral cavity and in the esophagus, part - in the stomach (in ruminants - proventriculus and abomasum), the bulk - in the small intestine, part - in the large intestine. In chickens, water is mainly absorbed by the mucous membrane of the cecum. The mucous membranes of the alimentary canal in cattle absorb about 100 liters of water during the day, and 75% of this water comes from digestive juices.

Water particles, together with digested nutrients, penetrate deep into the epithelium of the mucous membranes as a result of diffusion and osmosis, partly through pinocytosis and active transport. Along the endoplasmic reticulum they gradually move from the apical edge of the cell to the basal one, enter the intercellular space, and then into the intercellular fluid, capillaries, venules, subepithelial and submucosal venous networks of the intestinal villi, mesenteric veins, portal vein and liver, and then into the systemic circulation . Some water enters through the lymphatic system.

Intermediate water exchange. After absorption, water is transported to various organs, tissues and cells. Water is transported to tissues and cells mainly by blood proteins - albumins and globulins. Water penetrates cells directly (directly) or indirectly (through intercellular fluid). The exchange of water in the body is part of the general metabolism. Sodium salts, especially chlorides, promote the accumulation of water in tissues, causing swelling of colloids. Calcium salts, on the contrary, reduce the binding of water by proteins, stimulating its removal from the body. Therefore, patients with inflammatory processes are recommended to administer calcium chloride intravenously, as it reduces exudation processes.

Water exchange is characterized water balance- the ratio of water taken in and released from the body. At water equilibrium, the amount of water entering

body water is equal to the amount excreted. Positive water balance is typical for growing animals, water balance is typical for adult animals, negative water balance is typical for aging organisms, as well as for animals that do not receive the required amount of drinking water, especially during transportation and migration.

Final water exchange. Water is excreted from the body with urine (up to 50%), then and exhaled air (up to 35%), with feces (up to 15%). The share of excretory organs in water metabolism varies depending on environmental conditions, the type and age of the animal, and its functional state. For example, if a horse’s body receives 14-18 liters of water per day, then 4-8 liters are excreted through the urine, 6-12 liters through the lungs and skin, 4-5 liters through feces, and the volume of water circulating through the intestines is - 80-90 l.

Regulation of water metabolism. Regulation of water metabolism is carried out neurohumorally, in particular by various parts of the central nervous system: the cerebral cortex, the diencephalon and medulla oblongata, the sympathetic and parasympathetic ganglia.

Many endocrine glands are involved in the regulation of water metabolism. Some hormones have an antidiuretic effect: for example, the hormones vasopressin, aldosterone, deoxycorticosterone. Other hormones stimulate the excretion of water by the kidneys: thyroxine, parathyroid hormone, androgens and estrogens.

Pathology of water metabolism. Water metabolism is disrupted in many diseases. These disorders are based on morphofunctional changes in organs involved in general water metabolism and disorders of neurohumoral regulation.

Often the cause of pathology of water metabolism can be general and water starvation of the body. At the same time, hunger edema develops. Some diseases (tetanus, botulism, rabies, Aueszky's disease) make it difficult to take in water and a negative water balance occurs. Certain diseases (cholera, plague,

diabetes, gastritis and enteritis) lead to diabetes and excessive tissue loss of water. In some pathological conditions, water circulation in tissues and organs is difficult and a positive water balance occurs, especially in diseases of the kidneys, heart, etc.

Often the causes of water metabolism disorders are damage to the centers of the nervous system and endocrine glands.

Security questions

1. What is the importance of water for the animal body?

2. What are the main stages of water exchange in the body of animals?

3. How is water metabolism regulated?

4. What do you know about the pathology of water metabolism?

In fact, the role of water is multifaceted and difficult to list. Among its most obvious functions are:

1. Participation in enzymatic hydrolysis reactions. That's why

• catabolism in the cell of any polymer molecules (triacylglycerols, glycogen) and obtaining energy from them cannot occur without water,
• Digestion of nutrients is impaired in a state of water deficiency.

2. Formation cell membranes based on the amphiphilicity of phospholipids, i.e. on the ability of phospholipids to automatically form a polar membrane surface and a hydrophobic internal phase. As a consequence, with a decrease in the volume of intra- and extracellular water, some phospholipids turn out to be “extra” and deformation of cell membranes occurs.

3. Water shapes hydration shell around molecules. This provides

• the solubility of substances, in particular enzyme proteins, and the proper interaction of their surface hydrophilic amino acids with the surrounding aquatic environment. When the proportion of water in the medium decreases, the interaction worsens, the conformation of the enzyme changes and, therefore, the rate of enzymatic reactions varies,
• transport of substances in the blood and in the cell.

4. Water creates the active volume of the cell and intercellular space. The binding of water with the organic structures of the intercellular matrix - collagen, hyaluronic acid, chondroitin sulfates and other compounds provides turgor and tissue elasticity. This is clearly manifested in extreme dehydration of the body, when there is a collapse of the eyeballs and inelasticity of the skin.

As an example of the manifestation of hidden water deficiency, we can point out joint degeneration due to arthrosis. In the preclinical stage, dryness and roughness of the cartilage surfaces lead to increased friction and adhesion in the joint, which manifests itself as creaking and crunching sounds heard during movement. Subsequently, thinning and abrasion of the articular cartilage, a decrease in its shock-absorbing properties, the appearance of pain and the onset of the clinical stages of osteoarthritis develop.

5. Condition of liquid media body (blood, lymph, sweat, urine, bile) directly depends on the amount of water in them. Thickening and concentration of these liquids leads to a decrease in the solubility of their components - salts, organic substances, and increased crystal formation in urine and bile.

Thus, if other factors are present, such as excess oxalates or uric acid (for urolithiasis) or deficiency of lipotropic substances (for cholelithiasis) water deficiency potentiates the development of these diseases.

6. Sufficient amount of water maintains blood pressure stability. With a lack of water, the secretion of vasopressin and angiotensin is activated, part of the effects of which are aimed at

• constriction of blood vessels to bring blood volume into line with the capacity of the vascular bed,
• increasing blood pressure to ensure blood supply to the brain, kidneys and other organs.

Regular lack of water leads to constant contraction of vascular smooth muscles, their “training,” thickening of the muscle layer and, as a result, more pronounced vascular tone in response to normal stimuli and natural hormonal levels. Developing essentialarterial hypertension.

Sources of water in the cell

There are two sources of water for cellular metabolism:

1. Water, coming from food– per day the adult body should enter in the form of pure (!) water at least 1.5 liters or based on 25-30 ml/kg masses. Additionally, up to 1.5 liters can be supplied with drinks, liquid and solid food. For a child of the first year of life, the daily water requirement is 100-165 ml/kg weight, which is associated with b O a larger amount of extracellular fluid and the ease of its loss during exposure to the body.

2. Water formed during catabolism and oxidative phosphorylation - metabolic water, on average 400 ml.

Often this source of water is overestimated and considered sufficient to cover water deficits, citing the example of camels and the fat in their humps. However, an elementary calculation shows that at rest, even with complete fasting, to provide the human body with daily energy (2100-3500 kcal), 225-380 g of fat is needed (the value of triacylglycerol oxidation is 9.3 kcal/g). It is known that when complete oxidation of 1 g of fat produces 1.09 ml of water, i.e. There will be only 245-414 ml of such water per day.

Camels are capable of losing up to 25% of their weight due to water loss without complications for their well-being. Their ability to survive in hot desert conditions is not due to fat reserves, but to completely different reasons:

• oval red blood cells are less sensitive to blood thickening,
• water vapor of exhaled air completely condenses on the walls of the nasal passages (nostrils) and returns to the body,
• breathing rate is lower,
• body temperature varies from 35°C to 41°C depending on the environment, which prevents excess sweating,
• there is a high reabsorption of water from the large intestine, their droppings contain 6-7 times less water than that of cattle and consist of almost dry plant waste,
• There is no urea in the urine, an osmotically active substance that retains water, which reduces the volume of urine.

Removing water from the body

Water is removed by several systems:

1. Lungs. Water is excreted unnoticed by a person through exhaled air; these are imperceptible losses (on average 400 ml/day). The proportion of excreted water may increase with deep breathing, breathing dry air, hyperventilation, artificial ventilation without taking into account air humidity.

2. Leather. Loss through the skin may be

• imperceptible - in this case almost pure water is removed (500 ml/day),
• tangible – sweating when body or environmental temperature rises, during physical work (up to 2.0 liters per hour).

3. Intestines – 100-200 ml/day is lost, the amount increases with vomiting and diarrhea.

4. The kidneys excrete up to 1000-1500 ml/day. The rate of urine excretion in an adult is 40-80 ml/h, in children – 0.5 ml/kg h.

Under normal conditions, thanks to the kidneys, water is released from the body in an amount corresponding to the volume of fluid taken.

Some water is always removed regardless of the water diet, even during dry fasting. It's called obligate water loss(about 1400 ml per day). Obligate water loss refers to the removal of water from Then, exhaled air, feces And urine. At the same time, the proportion of water lost through the kidneys, even with the most concentrated urine, is up to 50% all losses.

Regulation of water balance

In the body for conservation water, two antidiuretic systems are responsible:

1. Antidiuretic hormone(vasopressin) – its secretion and synthesis increases with:

• activation baroreceptors heart as a result of a decrease in blood pressure, with a decrease in intravascular blood volume by 7-10%,
• excitement osmoreceptors hypothalamus and portal vein - with an increase in the osmolality of the extracellular fluid by even less than 1% (with dehydration, renal or liver failure),

In adulthood and old age, the number of osmoreceptors decreases and, consequently, the sensitivity of the hypothalamus to changes in osmolality decreases, which increases the risk dehydration, usually subclinical.

In the epithelial cells of the distal tubules of the kidneys and collecting ducts, the hormone stimulates the synthesis and incorporation of aquaporins into the apical cell membrane and the reabsorption of water.

2. Renin-angiotensin-aldosterone system(RAAS system) - activated by a decrease in pressure in the renal afferent arterioles or a decrease in the concentration of Na + ions in the urine of the distal tubules. The ultimate goal of this system is to enhance sodium reabsorption in the terminal sections of the nephron. This entails increasing the flow of water into the cells of the same sections and preventing its loss.

Water loss is caused by low activity of antidiuretic systems.

3. For purposeful deletion sodium and, accordingly, water are responsible for the third hormone. Natriuretic peptide(atriopeptin) is a vasodilating and natriuretic hormone produced in the secretory myocytes of the atria and ventricles in response to their stretching. Atriopeptin levels increase, for example, as a result of congestive heart failure, chronic renal failure, etc.

Natriuretic hormone enhances the excretion of Na + ions and water and reduces blood pressure due to:

• increasing glomerular filtration rate,
• inhibiting the reabsorption of Na + and Cl – ions in the proximal tubules and increasing their excretion, which reduces water reabsorption,
• decreased cardiac output and increased coronary tone,
• inhibition of renin secretion, effects of angiotensin II and aldosterone,
• increasing the permeability of histohematic barriers and increasing the transport of water from the blood into tissue fluid,
• dilatation of arterioles and decreased tone of veins.