CELL BIOLOGY

Inorganic substances

Among inorganic compounds living organisms play a special role in water. Water is the main medium in which the processes of metabolism and energy conversion take place. The water content in most living organisms is 60-70%. Water forms the basis of the internal environment of living organisms (blood, lymph, intercellular fluid). The unique properties of water are determined by the structure of its molecules. In a water molecule, one Oxygen atom is covalently bonded to two Hydrogen atoms. The water molecule is polar (dipole). The positive charge is concentrated on the Hydrogen atoms, since Oxygen is more electrically negative than Hydrogen. A negatively charged Oxygen atom of one water molecule is attracted to a positively charged Hydrogen atom of another molecule, thus forming a hydrogen bond, which is 15-20 times weaker than a covalent one. Therefore, hydrogen bonds are easily broken, which is observed, for example, during the evaporation of water. Due to the thermal motion of molecules in water, some hydrogen bonds are broken, some are formed. Thus, the molecules are mobile in a liquid state, which is very important for metabolic processes. Water molecules easily penetrate cell membranes. Due to the high polarity of the molecules, water is a solvent for other polar compounds. Depending on the ability to distinguish certain compounds in water, they are conventionally divided into hydrophilic, or polar, and hydrophobic, or non-polar. The hydrophilic compounds, soluble in water, include most salts. Hydrophobic compounds (almost all fats, some proteins) contain non-polar groups that do not form hydrogen bonds, so these compounds do not dissolve in water. It has a high heat capacity and at the same time high thermal conductivity for liquids. These properties make water ideal for maintaining thermal equilibrium in the body.

To maintain the vital processes of individual cells and the body as a whole, mineral salts are of great importance. Living organisms contain dissolved salts (in the form of ions) and salts in a solid state. Ions are divided into positive (cations of metal elements K +,N a +, Ca 2+, M 2+, etc.) and negative (hydrochloric acid anions - Cl -, sulfate - Н SO 4 -, S O 4 2-, carbonate - НСО 3 -, phosphate - Н 2 РО 4 -, НРО 4 2-, etc.). Different concentrations of K + andN a + in the cell and intercellular fluid causes a potential difference on the cell membrane; change in membrane permeability by K + andN a + under the influence of irritation provides the emergence of nervous and muscular excitement. Anions of phosphate acid maintain a neutral reaction of the intracellular environment (pH \u003d 6.9), anions carboxylic acid - slightly alkaline reaction of blood plasma (pH \u003d 7.4). Calcium compounds (CaCO 3 ) are part of the shells of mollusks and protozoa, crayfish shells. Chloric acid creates an acidic environment in the stomachvertebrates and humans, this provides the activity of enzymes in gastric juice. The remains of sulfuric acid, attaching to water-insoluble compounds, ensuring their solubility, which contributes to the removal of these compounds from cells and the body.

Environment is a set of living conditions for living beings. Allocate the external environment, i.e. a complex of factors outside the body, but necessary for its life, and the internal environment.

The internal environment of the body is called the totality of biological fluids (blood, lymph, tissue fluid) that wash cells and tissue structures and take part in metabolic processes. Claude Bernard proposed the concept of "internal environment" in the 19th century, thereby emphasizing that, in contrast to the changeable external environment in which a living organism exists, the constancy of the vital processes of cells requires a corresponding constancy of their environment, i.e. internal environment.

A living organism is an open system. An open system is called a system, for the existence of which a constant exchange of matter, energy and information with the external environment is required. The interrelationships between the body and the external environment ensure the supply of oxygen, water and nutrients to the internal environment, the removal of carbon dioxide and unnecessary, and sometimes harmful, metabolites from it. The external environment supplies the body with a huge amount of information perceived by numerous sensitive formations of the nervous system.

The external environment has not only beneficial, but also harmful influences for the vital activity of the organism. However, a healthy organism functions normally if the environmental influences do not exceed the limits of admissibility. This dependence of the body's vital activity on the external environment, on the one hand, and the relative stability and independence of life processes from changes in the environment, on the other hand, is ensured by a property of the organism called homeostasis (homeostasis). The body is an ultra-stable system that itself searches for the most stable and optimal state, keeping various parameters of functions within the boundaries of physiological ("normal") fluctuations.

Homeostasis is the relative dynamic constancy of the internal environment and the stability of physiological functions. This is precisely dynamic, not static constancy, since it implies not only the possibility, but the need for fluctuations in the composition of the internal environment and parameters of functions within physiological boundaries in order to achieve an optimal level of vital activity of the organism.

The activity of cells requires an adequate function of supplying them with oxygen and effective flushing of carbon dioxide and other waste substances or metabolites from them. To restore decaying protein structures and extract energy, cells must receive plastic and energetic material that enters the body with food. All this cells receive from the microenvironment surrounding them through tissue fluid. The constancy of the latter is maintained due to the exchange of gases, ions and molecules with the blood. Consequently, the constancy of the blood composition and the state of the barriers between blood and tissue fluid, the so-called histohematological barriers, are the conditions for homeostasis of the cell microenvironment. The selective permeability of these barriers provides a certain specificity of the composition of the microenvironment of cells, which is necessary for their functions.

On the other hand, interstitial fluid is involved in the formation of lymph, exchanges with lymphatic capillaries draining tissue spaces, which makes it possible to effectively remove large molecules from the cellular microenvironment that are unable to diffuse through the histohematogenous barriers into the blood. In turn, the lymph flowing from the tissues through the thoracic lymphatic duct enters the blood, ensuring the maintenance of the constancy of its composition. Consequently, in the body between the fluids of the internal environment, there is a continuous exchange, which is a prerequisite for homeostasis.

The interconnections of the components of the internal environment with each other, with the external environment and the role of the main physiological systems in the implementation of the interaction of the internal and external environment are shown in Figure 2.1. The external environment affects the body through the perception of its characteristics by sensitive devices of the nervous system (receptors, sensory organs), through the lungs, where gas exchange takes place, and through the gastrointestinal tract, where water and food ingredients are absorbed. The nervous system exerts its regulatory effect on cells due to the release of special mediators at the endings of the nerve conductors - mediators, entering through the microenvironment of cells to special structural formations of cell membranes - receptors. The influence of the external environment perceived by the nervous system can also be mediated through the endocrine system, which secretes special humoral regulators - hormones - into the blood. In turn, the substances contained in the blood and tissue fluid, to a greater or lesser extent, irritate the receptors of the interstitial space and the bloodstream, thereby providing the nervous system with information about the composition of the internal environment. Removal of metabolites and foreign substances from the internal environment is carried out through the excretory organs, mainly the kidneys, as well as the lungs and the digestive tract.



The constancy of the internal environment is the most important condition for the vital activity of the organism. Therefore, deviations in the composition of fluids in the internal environment are perceived by numerous receptor Fig.2.1. Diagram of the interconnections of the internal environment of the body.

structures and cellular elements with the subsequent inclusion of biochemical, biophysical and physiological regulatory reactions aimed at eliminating the deviation. At the same time, the regulatory reactions themselves cause changes in the internal environment in order to bring it into conformity with the new conditions of the organism's existence. Therefore, the regulation of the internal environment is always aimed at optimizing its composition and physiological processes in the body.

The boundaries of homeostatic regulation of the constancy of the internal environment can be rigid for some parameters and plastic for others. Accordingly, the parameters of the internal environment are called rigid constants if the range of their deviations is very small (pH, ion concentration in the blood), or plastic constants (glucose, lipids, residual nitrogen, interstitial fluid pressure, etc.), i.e. subject to relatively large fluctuations. Constants vary with age, social and occupational conditions, time of year and day, geographic and natural conditions, and also have gender and individual characteristics. Environmental conditions are often the same for more or fewer people living in a certain region and belonging to the same social and age group, but the constants of the internal environment may differ for different healthy people. Thus, homeostatic regulation of the constancy of the internal environment does not mean the complete identity of its composition in different individuals. However, in spite of individual and group characteristics, homeostasis ensures the maintenance of normal parameters of the internal environment of the body.

Usually, the norm is called the average values \u200b\u200bof the parameters and characteristics of the vital activity of healthy individuals, as well as the intervals within which the fluctuations of these values \u200b\u200bcorrespond to homeostasis, i.e. are able to keep the body at the level of optimal functioning.

Accordingly, for general characteristics of the internal environment of the body, normally the intervals of fluctuations of its various indicators are usually given, for example, the quantitative content of various substances in the blood of healthy people. At the same time, the characteristics of the internal environment are interrelated and interdependent quantities. Therefore, shifts in one of them are often compensated by others, which is not necessarily reflected in the level of optimal functioning and human health.

The internal environment is a reflection of the most complex integration of the vital activity of different cells, tissues, organs and systems with the influences of the external environment.

This determines the particular importance of the individual characteristics of the internal environment that distinguish each person. The individuality of the internal environment is based on genetic individuality, as well as long-term exposure to certain conditions of the external environment. Accordingly, the physiological norm is the individual optimum of life, i.e. the most consistent and effective combination of all life processes in the real conditions of the external environment.

2.1. Blood as the internal environment of the body.

Figure 2.2. The main constituents of blood.

Blood consists of plasma and cells (shaped elements) - erythrocytes, leukocytes and platelets, which are in suspension (Fig. 2.2.). Since plasma and cellular elements have separate sources of regeneration, blood is often secreted into an independent type of tissue.

The functions of the blood are diverse. These are, first of all, in a generalized form, the functions of transport or transfer of gases and substances necessary for the vital activity of cells or to be removed from the body. These include respiratory, nutritional, integrative-regulatory, and excretory functions (see Chapter 6).

Blood also performs a protective function in the body, due to the binding and neutralization of toxic substances entering the body, binding and destruction of foreign protein molecules and foreign cells, including those of infectious origin. Blood is one of the main environments where the mechanisms of specific protection of the body from foreign molecules and cells are carried out, i.e. immunity.

Blood is involved in the regulation of all types of metabolism and temperature homeostasis, is the source of all fluids, secretions and excretions of the body. The composition and properties of blood reflect shifts in other fluids of the internal environment and cells, and therefore blood tests are the most important diagnostic method.

The amount or volume of blood in a healthy person is within 68% of body weight (4 - 6 liters). This condition is called normovolemia. After excessive intake of water, the blood volume may increase (hypervolemia), and with hard physical work in hot workshops and excessive sweating, it may fall (hypovolemia).

Figure 2.3. Determination of hematocrit.

Since blood is composed of cells and plasma, the total blood volume also consists of the plasma volume and the cell volume. The part of the blood volume falling on the cellular part of the blood is called hematocrit (Fig. 2.3.). In healthy men, the hematocrit is within 4448%, and in women - 4145%. Due to the presence of numerous mechanisms for the regulation of blood volume and plasma volume (volumoreceptor reflexes, thirst, nervous and humoral mechanisms of changes in the absorption and excretion of water and salts, regulation of the protein composition of blood, regulation of erythropoiesis, etc.), hematocrit is a relatively rigid homeostatic constant and its long and persistent change is possible only in high altitude conditions, when adaptation to low partial pressure of oxygen enhances erythropoiesis and, accordingly, increases the proportion of blood volume accounted for by cellular elements. Normal values \u200b\u200bof hematocrit and, accordingly, the volume of cellular elements are called normocythemia. An increase in the volume occupied by blood cells is called polycythemia, and a decrease is called oligocythemia.

Physics chemical properties blood and plasma. The functions of blood are largely determined by its physicochemical properties, among which the most important are osmotic pressure, oncotic pressure and colloidal stability, suspension stability, specific gravity and viscosity.

The osmotic pressure of blood depends on the concentration in the blood plasma of molecules of substances dissolved in it (electrolytes and non-electrolytes) and is the sum of the osmotic pressures of the ingredients contained in it. In this case, over 60% of the osmotic pressure is created by sodium chloride, and in total, inorganic electrolytes account for up to 96% of the total osmotic pressure. Osmotic pressure is one of the rigid homeostatic constants and in a healthy person averages 7.6 atm with a possible fluctuation range of 7.38.0 atm. If the liquid of the internal environment or an artificially prepared solution has the same osmotic pressure as normal blood plasma, such a liquid medium or solution is called isotonic. Accordingly, a fluid with a higher osmotic pressure is called hypertonic, and a fluid with a lower osmotic pressure is called hypotonic.

Osmotic pressure ensures the transition of the solvent through a semi-permeable membrane from a less concentrated solution to a more concentrated solution, therefore it plays an important role in the distribution of water between the internal environment and the cells of the body. So, if the interstitial fluid is hypertonic, then water will enter it from both sides - from the blood and from the cells, on the contrary, when the extracellular medium is hypotonic, water passes into the cells and blood.

Basic literature

1. Human physiology.Edited by V.M. Pokrovsky, G.F. Korotko. - Medicine, 2003 (2007) - S. 229-237.

2. Human physiology In two volumes. Volume I.Edited by V.M. Pokrovsky, G.F. Korotko. - Medicine, 1997 (1998, 2000, 2001). S. 276-284.

For a long time, blood was recognized as a powerful and exceptional force: sacred oaths were fastened with blood; the priests made their wooden idols “cry blood”; the ancient Greeks sacrificed blood to their gods [Matthew 1]. Some philosophers of ancient Greece considered blood to be the bearer of the soul. The ancient Greek physician Hippocrates prescribed the blood of healthy people to the mentally ill. He thought that there was a healthy soul in the blood of healthy people [Mt. 2].

Blood mobility is the most important condition for the life of an organism [Mf3].

We continue to study circulatory system ... Remember what constitutes the circulatory system? Correctly! Cardiovascular system + blood .

If the cardiovascular system can be called a transport system, then blood is a transported medium.

Just as it is impossible to imagine a state without transport communication lines, so it is impossible to understand the existence of a person or an animal without the movement of blood through the vessels, when oxygen, water, proteins and other substances are carried to all organs and tissues. [Mf4]

Blood is the most important component of the internal environment of the human body, therefore, before proceeding to the characteristics of blood, it is necessary to get acquainted with the basic issues of the physiology of the internal environment.

1. The concept of "internal environment of the body [Mf5]"

Primary organisms developed in the oceans. Water brought them nutrients and accepted metabolic products [B6]. In multicellular organisms, most of the cells have lost contact with the environment, and this environment for the creatures that emerged from the water has changed significantly (!). There was water, it became dry and not always comfortable. But a piece of that ocean splashes in us now, being the basis of the internal environment of the organism.

Internal environment of the body[Mt7] - the totality liquids directly involved in metabolic processes and maintaining the homeostasis of the body [Mf8]. [a]

Concept internal environment of the body introduced into physiology K. Bernard in 1854-1857. [b]

The internal environment is characterized by dynamic constancy [Mt9].

To describe this state in 1929 W. Cannon introduced the term homeostasis [Mt10] [c].

In connection with the identification of the role of biorhythms in the activity of a living organism, chronobiology began to operate with the term not “ homeostasis ", and " homeokinesis "or " homeoresis ", Which is understood not only the value of the parameters, but also the process of their change in time.

However, in the literature, the term "homeostasis" is more often used, while they mean that the constancy of the internal environment is relative [Mf11].

The boundaries of homeostasis can be rigid and flexible. Their performance depends on species, individual, sexual and other conditions. Rigid constants are the parameters of the internal environment which determine the optimal enzyme activity, i.e. the possibility of carrying out metabolic processes [Mf12] .-- 162- C.13]

Total water, body fluids and internal fluids

The human body is mostly water.

Its relative content changes with age from 75% in a newborn to 55% in the elderly [B14]].

In women, the relative water content is less than that of men by 5%.

The balance of water (intake, education, circulation, participation in metabolism, excretion) is the topic of other lectures on water-salt metabolism.

Water is the basis of all liquid media [Mf15].

The body fluids are divided into the following compartments [d]:

Intracellular (intracellular [B16]) fluid

Extracellular (extracellular) fluid

Intravasal fluid

Blood plasma

Extravasal fluid

Intercellular fluid (syn: tissue, interstitial)

Crystallization (structured) water of bone and cartilage (15% of all body water [B17])

Transcellular [B18] (specialized) fluids

Fluids of closed cavities (i.e., not having direct communication with the external environment). [Mt 19]

CSF (synonyms - cerebrospinal or cerebrospinal fluid)

Synovial (intra-articular [B20]) fluid

Lubrication of serous membranes (peritoneum, pleura, pericardium [B21])

Eyeball fluids

Inner ear fluids

Open cavity fluids [B22]

Secrets of the digestive glands (saliva, gastric juice, bile, pancreatic juice, intestinal juice)

Moisturizing fluids (respiratory tract, middle and outer ear).

Body fluids [Mf23] (urine, sweat, tears, milk)

Note! The fluid of the formed elements of blood is intracellular water, therefore blood plasma, and not all blood, belongs to the extracellular fluid.

The body fluids include:

tissue (intercellular) fluid.

However [B24], specialized fluids should also be included in this set.

For more information on CSF see [++ 601 ++] C.129-130.

In the brain, there is a distinction between cerebrospinal fluid and intercellular fluid (extracellular spaces of the brain [B25]). Do not equate these concepts!

Specialized fluids are often understood to mean the fluids of closed body cavities. Do not forget about the fluids of the open cavities of the body. All of these fluids are involved in maintaining the homeostasis of the body. How will you feel when answering if your mouth is dry?

As a rule, emphasize a special role tissue fluid , since only it contacts the cells of the body [B26]. They call her true [B27] the internal environment of the body. It is believed that basis internal environment is blood , and the immediate nutrient medium - tissue fluid [B28]

Sometimes a cage directly (without the mediation of interstitial fluid) contacts and exchanges with other fluids of the internal environment. For example, blood, in direct contact with the endocardium and vascular endothelium, ensures their vital activity [Mf29].

The interstitium (interstitial space) (lat. Interstitium gap, gap) is an integral part of the connective tissue [Mf30] and has a rather complex structure [Mf31].

It is helpful to remember the following relationships:

[B32]

Distribution of water in the body depending on age in% of body weight [B33]

Distribution of water in the body depending on gender with an average body weight of 70 kg [B34]

Distribution of water in a woman's body at 38-40 weeks of gestation in% of body weight [B35]

3. Histohematogenous barriers [Mf36]

On fluid compartments separated by external and internal barriers [Mt37].

External barriers - skin, kidneys, respiratory organs, digestive tract, liver (!).

Internal barriers - histohematological.

Insulating (specialized):

Hematoencephalic

Hematoneuronal

Hemato-testicular

Hematoophthalmic

Partially insulating:

Hematocholic

Hematocorticosupprarenal

Hematothyroid

Hematopancreatic

Non-insulating:

Myohematous

Hematoparathyroid

Hematomedullosuprarenal

The structural basis of histohematogenous barriers is the capillary endothelium [B38]. The biological membrane is the barrier between the intracellular and extracellular fluid compartments. Biological membranes of cell organelles (intracellular barriers divide fluids into intracellular compartments [B39]. [B40]

Water not separated by biological barriers is also compartmentalized. Water associated with proteins, other organic compounds, ions (forms hydration shells) is called hydration.

Bound water, which is hardly involved in the general water cycle in the body, is called immobile (motionless) .Water not bound, easily involved in the general water cycle in the body is called mobile .

Extracellular liquids have quite similar [B42]composition , which is associated with a constant exchange between blood plasma, lymph, interstitial fluid. Intracellular liquid media are very different among themselves [B43].

The difference in the composition of the liquid compartments determines the intensity of metabolism between them.


Similar information.


Having become acquainted with the elements present in living organisms, let us now turn to the compounds, which these elements are part of (Fig.). It also reveals a fundamental similarity between all living organisms. Most of all they contain water. In all organisms, we also find simple organic compounds that play the role of “building blocks” from which larger molecules are built. These are, above all, amino acids, monosaccharides, organic acids, alcohols, nucleotides and some other substances.

Water.Among the inorganic compounds of living organisms, a special role belongs to water. It is the main medium in which the processes of metabolism and energy take place. The water content in living organisms is 60 - 75% of their mass, and in some (for example, jellyfish) - up to 98%. Water forms the basis of the internal environment of organisms (blood, lymph, tissue fluid). The highest water content in the body is observed during the embryonic period (95%) and gradually decreases with age. The amount of water is not the same in different tissues. So, in the gray matter of the brain its content is 85%, in the bones - 20%, in the enamel of the teeth - 10%. The more water in the cells of the body, the more intensive the metabolism is. If the body loses 20% of water, death can occur. Without water consumption, a person can live no more than five to seven days.

Water properties. As you know, life originated in water and still remains closely associated with it. For this reason, the physical and chemical properties of water are of fundamental importance for life processes. Compared to other liquids, water has a relatively high boiling and evaporation point.

An HO molecule consists of two hydrogen atoms covalently bonded to an oxygen atom (Fig.).

The H - O - H bonds are located at an angle to each other. The oxygen atom, as a more electronegative element, attracts common electron pairs from hydrogen atoms. The hydrogen atoms acquire a partially positive charge, and the oxygen atom partially negative, ᴛ.ᴇ. the molecule is polar and is electric dipoleAs a result, an electrostatic interaction occurs between water molecules, and, since opposite charges are attracted, water molecules tend to "stick together" (Fig.). These interactions, weaker than conventional ionic bonds, are called hydrogen bonds.The energy of a hydrogen bond is 10-40 times less than the energy of a covalent bond. Each water molecule, like a small magnet, attracts four more molecules due to the formation of hydrogen bonds. Due to the formation of hydrogen bonds, the molecules are bound to one another, which causes the initial liquid state of water at temperatures from 0º to 100 ºС and forms solid ice crystals at temperatures below 0ºС.

Functions of water. Water determines volume and intracellular pressure (turgor) cells. It is able to form a water membrane around some compounds (for example, proteins), which prevents their interaction. This water is called related (structured). It makes up 4 - 5% of the total amount of water in the body. The other part of water (95 - 96%), not associated with compounds, is called free.It is she who is a universal solvent, better than most of the known fluids.

Taking into account the dependence on solubility in water, the compounds are conventionally divided into polar, or hydrophilic (from the Greek. hydor- water, branch- to love) and non-polar, or hydrophobic (from the Greek. phobos- fear). Hydrophilic substances are many mineral salts, sugars, alcohols, acids, etc. Hydrophobic substances are characterized by non-polar covalent bonds and, therefore, they are insoluble in water. Paraffin, gasoline, kerosene, etc. are hydrophobic. Hydrophobic solids are not wetted with water.

Water like universal solvent plays an extremely important role. Most of the chemical reactions in the body only take place in aqueous solutions. Substances penetrate into the cell, and waste products are removed from it mainly in a dissolved form. Water is directly involved in reactions hydrolysis - splitting of organic compounds with attachment to the place of rupture of ions of the water molecule (H + and OH).

Water is also electron source in the reactions of photosynthesis. The splitting off of electrons from water molecules leads to the appearance of a by-product for plant cells - oxygen, which, however, is a substance of planetary importance.

The regulation of the thermal regime of organisms is also associated with water. She is characterized by high heat capacity, ᴛ.ᴇ. the ability to absorb heat with slight changes in its own temperature. Thanks to this, water prevents sudden changes in temperature in cells and in the body as a whole, even when it fluctuates significantly in the environment. Evaporation of water from transpiration and perspiration?

When water evaporates by organisms (transpiration and perspiration), a lot of heat is wasted, which protects them from overheating. Due to the high thermal conductivity water ensures an even distribution of heat between the tissues of the body (for example, through the circulatory system, circulation of fluid in the body cavities).

Substances dissolved in water can change its properties, in particular the freezing and boiling point, which is of great biological importance. Thus, in the cells of frost-resistant plants and cold-blooded animals, with the onset of winter, the concentration of soluble proteins, carbohydrates and other compounds increases, which lower the temperature of the transition of water to the crystalline state, which prevents their death.

Mineral salts and acids. In addition to water, mineral salts are important for the maintenance of the vital activity of the organism as a whole and of its cells. In living organisms, they are either dissolved (dissociated into ions) or in a solid state. The most important among the ions are the cations K +, Na +, Ca2 +, Mg2 + and the anions НСО, НРО, HPO, Cl–, НSO, SO.

The general content is not organic matter in different cells varies from one to several percent. Their role in the cell is varied. Thus, different concentrations of K + inside and Na + outside cells lead to the appearance of a difference in electrical potentials on the cytoplasmic membrane, which is very important for the transmission of nerve impulses, as well as for the transport of substances through membranes. With a decrease in this difference, the excitability of the cells decreases.

The regulatory function and activation of many enzymes are performed by Ca 2+ and Mg 2+. Ca2 + ions are necessary for the implementation of muscle contraction, blood clotting, they are part of the bones. Mg2 + ions are part of bones and teeth, activate energy exchange and ATP synthesis.

Some ions are required for the synthesis of important organic substances. For example, phosphoric acid residues are part of nucleotides, ATP; ion Fe 2+ - in the composition of hemoglobin, Mg 2+ - in the composition of chlorophyll, etc. Ions NO, NH are a source of nitrogen atoms ͵ ion SO- sulfur atoms, which are necessary for the synthesis of amino acid molecules.

Calcium compounds (CaCO) are found in shells of molluscs, crustaceans and other animals. In some protists (radiolarians), the intracellular skeleton is built of silicon dioxide (SiO) or strontium sulfate (SrSO 4).

Inorganic acids also perform important functions in the body. So, hydrochloric acid creates an acidic environment in the stomach of vertebrates and humans, thereby ensuring the activity of enzymes in gastric juice.

Acidity of the environment.The course of biochemical reactions in living organisms is significantly influenced by the concentration of hydrogen ions (H) - acidity of the environment. In neutral solutions, this concentration is 10 mol / l, in acidic solutions it is greater than this value, in alkaline solutions it is less. In chemistry, the so-called hydrogen index (pH). The length of the pH scale is from 0 to 14. It should be said that for neutral solutions pH \u003d 7, for acidic pH< 7, для щелочных рН > 7. Inside the cells, the medium is neutral or slightly alkaline (pH \u003d 7.0-7.3); in blood, the pH value usually varies within the range of 7.35 - 7.45, which is somewhat higher than in cells.

The pH varies in the digestive tract and in the body's secretions. Extreme pH values \u200b\u200bare observed in the stomach (about 2) and in the small intestine (over 8). Due to the fact that the kidneys can excrete both cations and anions, significant variations in pH (4.8 - 7.5) are observed in urine.

The concept of buffer solutions.The organism as a whole and its individual cells maintain the acidity of the environment at a constant level due to the buffering properties of their contents. Buffer it is customary to call a solution containing a mixture of a weak acid and its soluble salt... When the concentration of hydrogen ions increases, the free anions, the source of which is the salt, easily combine with the free Ni ions and remove them from the solution. When the acidity decreases, additional hydrogen ions are released. Thus, a relatively constant concentration of H ions is maintained in the buffer solution. The ability to maintain a slightly alkaline reaction of the extracellular medium is provided by HCO ions; neutral or slightly alkaline intracellular environment - ions HPO, HPO.

s 1. What is the water content of living organisms? What does it depend on? 2. What are the properties of water as the main component of the internal environment of organisms? What features of the structure of water molecules provide its properties? 3. Does water participate in chemical reactions in organisms? Give examples of such reactions, if you know them. 4. Why is water a good solvent? 5. What are the main functions of water in living organisms? 6. Why are non-polar substances poorly soluble in water? 7. What is the state of the minerals in the cell? 8. What is the role of minerals in the cell? 9. What are buffer properties and how are they determined?

Water in a living organism

Water accounts for the bulk of the mass of any living creature on Earth. In an adult, water makes up more than half of the body weight. Precisely in an adult, because at different periods of life, the water content in the body changes. In the embryo, it reaches 97%; immediately after birth, the total amount of water in the body quickly decreases - in a newborn, it is already only 77%. Further, the water content continues to gradually decrease until it becomes relatively constant in adulthood. On average, the water content in the body of men from 18 to 50 years old is 61%, women - 54% of the body weight. This difference is due to the fact that the body of adult women contains more fat; when fat is deposited, the body weight increases and the proportion of water in it decreases (in obese people, the water content can be reduced to 40% of body weight). After 50 years, the human body begins to "dry out": there is less water in it.

Most of the water - 70% of all body water - is inside the cells, as part of the cellular protoplasm. The rest is extracellular water: part of it (about 7%) is inside the blood vessels and forms blood plasma, and part (about 23%) washes the cells - this is the so-called interstitial fluid.

Back in 1858, the famous French physiologist Claude Bernard formulated the principle of the constancy of the internal environment of an organism - something like the law of conservation of mass - energy for living beings. This principle says: the intake of various substances into the body should be equal to their release. It is clear that the water consumption must be equal to the flow rate. How does a person spend water?

It is rather difficult to take into account water losses of the body, because a considerable part of them falls on the share of so-called imperceptible losses. For example, water in the form of vapor is contained in the exhaled air - this is approximately 400 ml / day. About 600 ml / day of it evaporates from the surface of the skin. A little water is secreted by the lacrimal glands (and not only when we cry: the fluid secreted by them constantly washes the eyeball); water is also lost with droplets of saliva when talking, coughing, etc. Other ways of excretion of water are easier to account for: 800-1300 ml per day, excreted in the urine, and about 200 ml - with feces. If you add up all the above figures, you get about 2-2.5 liters; this figure is average, because water consumption can fluctuate greatly depending on external conditions, individual characteristics of exchange, or as a result of its disturbances.

In accordance with this, the daily requirement of an adult's body for water averages about 2.5 liters. This, however, does not mean at all that a person should drink at least 10 glasses of water every day: the bulk of the water we consume is contained in food. Part of the water is also formed directly in the body in the course of life - during the breakdown of proteins, fats and carbohydrates (endogenous water). For example, oxidation of 100 g of fat produces 107 ml of water, 100 g of carbohydrates - 55 ml. Therefore, the most beneficial (in terms of obtaining endogenous water) is fat. And it is no coincidence that significant fat deposits are observed just in those animals that have adapted for a long time to do without water from the outside, producing it in their bodies. Among them is the camel, a large animal of the desert. The reserve of fat in its hump, with complete oxidation, makes it possible to obtain about 40 liters of endogenous water, which is the daily requirement of the animal for it. Of course, a substantial supply of fat does not completely replace drinking water for a camel. Fatty deposits - a source of endogenous water, in addition to the camel, are found in the desert fat-tailed sheep breeds. Fat accumulates in the tails of some jerboas, under the skin of yellow and small gophers, hedgehogs, etc. Australian mice quench their thirst with exclusively endogenous water.

Not a single life process in a human or animal organism can take place without water, and not a single cell is able to do without an aqueous environment. With the participation of water, almost all functions of the body proceed. So, evaporating from the surface of the skin and respiratory organs, water takes part in the processes of thermoregulation.

The digestion process is the most important function of the body. The digestion process in the gastrointestinal tract takes place only in the aquatic environment. In this process, water plays the role of a good solvent for almost all food products.

The water drunk is first of all absorbed through the walls of the stomach and intestines into the blood and with it is evenly distributed throughout the body, passing from the blood into the interstitial fluid, and then into the cells. This exchange of water is quite intense. Being in a state of connection with water, food products (proteins, carbohydrates, fats, mineral salts) are also easily absorbed into the bloodstream and enter all organs and then body tissues.

The transition of water from blood to interstitial fluid is entirely subject to physical laws. The work of the heart creates hydrostatic pressure inside the vessels, tending to push the fluid through the vessel wall. This is counteracted by the osmotic pressure, which is created by substances dissolved in the blood. More precisely, the main role here is not played by osmotic pressure, but only that small part of it (approximately 1/220), which is formed by blood plasma proteins - this is the so-called oncotic pressure. The fact is that both water and low-molecular-weight solutes, which create the main part of the osmotic pressure, pass freely through the walls of the capillaries, but they are practically impermeable to proteins. And it is the oncotic pressure created by the proteins that keeps the water inside the capillary.

In the initial, arterial part of the capillary, the hydrostatic pressure is high - it is much higher than the oncotic one. Therefore, water, together with low-molecular substances dissolved in it, is squeezed out through the walls of the capillary into the intercellular space. In the final, venous part of the capillary, the hydrostatic pressure is much lower, because here the capillary expands. Oncotic pressure protein, here, on the contrary, increases, since part of the water has already left the capillary and the plasma volume has decreased, and the concentration of proteins in it has increased. Now the oncotic pressure becomes greater than the hydrostatic pressure, and here the water, which carries the waste products of the cells, flows from the intercellular space back into the vascular bed.

This is the general picture of the exchange of water between blood and tissues. True, this mechanism is not applicable in all cases; with its help, for example, it is impossible to explain the exchange of fluid in the liver. The hydrostatic pressure in the hepatic capillaries is not enough to cause the transfer of fluid from them to the interstitial space. It is not so much that they play a role here. physical lawshow many enzymatic processes.

From the interstitial fluid, water enters the cells. This process is also determined not only by the laws of osmosis, but also by the properties of the cell membrane. Such a membrane, in addition to passive permeability, which depends on the concentration of a particular substance on its different sides, also has the property of actively transferring certain substances even against the concentration gradient, that is, from a more dilute solution to a less dilute one. In other words, the membrane acts as a "biological pump". By regulating the osmotic pressure in this way, the cell membrane also controls the processes of water passing through it from the intercellular space into the cell and back.

The main way of removing water from the body is the kidneys; about half of the water leaving the body passes through them. The kidneys are one of the most energetically working organs, with more energy per unit of weight than any other. Of all the oxygen absorbed by humans, at least 8-10% is used in the kidneys, although their weight is only 1/200 of the body weight. All this testifies to the importance of the processes that take place in them.

More than 1000 liters of blood pass through the kidneys per day, which means that every drop of blood will visit here at least two hundred times per day. Here the blood is cleansed of unnecessary metabolic products, which it brings from all organs and tissues dissolved in plasma, i.e., ultimately, again in water.

When blood passes through the initial, arterial part of the renal capillary, about 20% of it due to high hydrostatic pressure (in renal capillaries it is twice as high as in ordinary capillaries) passes through the wall of the capillary into the cavity of the renal glomerulus - this is the so-called primary urine. At the same time, as in all other capillaries of the body, all substances dissolved in the plasma, except for proteins, pass through the wall of the renal capillary. Among them, in addition to the waste that must be removed from the body, there are also the necessary substances, the release of which would be a senseless waste. The body cannot afford this, and therefore in the renal tubule, where the primary urine enters from the renal glomerulus, a careful sorting is performed. Nutrients, various salts, and other compounds are constantly reabsorbed - they pass through the walls of the tubule back into the blood, into the capillary adjacent to the tubule. Complex enzymatic reactions play a leading role in this reabsorption process.

Together with useful substances, primary urine and water leave. In the initial section of the renal tubule, water is passively reabsorbed: it passes into the blood after actively reabsorbed sodium, glucose and other substances, leveling the resulting difference in osmotic pressure.

In the final section of the renal tubule, when the reabsorption of nutrients has been largely completed, the return of water to the blood is regulated by a different mechanism and depends only on how much the body needs this water itself. Nerve receptors are scattered in the walls of blood vessels, which react very subtly to changes in the water content in the blood. As soon as the water becomes less than needed, nerve impulses from these receptors enter the pituitary gland, where the hormone vasopressin begins to be released. Under the influence of it, the enzyme hyaluronidase is produced. The enzyme makes the walls of the renal tubules permeable to water, destroying the waterproof polymer complexes that make up their composition, as if opening a tap for water to exit through the tubule wall. As a result, water, now following the laws of osmosis, passes into the blood. The less water in the body, the more vasopressin is released, the more hyaluronidase is produced, the more water is absorbed back into the blood.

Ultimately, of all primary urine, only less than 1% is excreted by the kidneys in the form of "real" urine, which now contains only waste products and only unnecessary water for the body.

It has been experimentally established that at least 500 ml of urine is required daily to remove waste from the human body. If a person drinks a lot of water, it dilutes the urine, the specific gravity of which decreases. With insufficient intake of water into the body, when, after replenishing its losses through the skin and lungs, less than 500 ml remains in the kidneys, part of the waste products remains in the body and can cause its poisoning. This is precisely what water starvation is dangerous for.

Dehydration is especially difficult for a person. If the loss of water is not replenished, then as a result of disturbances in physiological processes, health worsens, performance decreases, and at high air temperature, thermoregulation is disturbed and overheating of the body may occur. With a moisture loss of 6–8% of the body weight, a person's body temperature rises, the skin turns red, the heartbeat accelerates, breathing becomes more rapid, turning into shortness of breath, muscle weakness, dizziness, headaches appear, and a semi-fainting state occurs. With the loss of 10% of water, irreversible changes in the body can occur. The loss of water in the amount of 15–20% at air temperatures above 30 ° is already fatal, and the loss of 25% of water is fatal even at lower temperatures.

Human waste is also released with sweat. On average, the surface of the human body is 1.5 m 2.

A person sweats a lot in extreme heat. For a day, he literally "gives out" a bucket of sweat: the air would be dry.

The main component of the liquid in such a bucket is ordinary, unremarkable water. Non-volatile and volatile components are dissolved in it. It's easy to get acquainted with non-volatile ones - salty sweat: about 1% NaCl, and even phosphates and sulfates. A lot of sweat and creatinine. But even experts are not very familiar with volatile components, but something is still known: cosmobiologists came to the conclusion that even a little sweating person through the skin releases so many substances that a three-cubic closed atmosphere per day will be saturated with harmful compounds above the maximum permissible norms. It doesn't matter on Earth, but you can't open a window in space.

To prevent astronauts from suffocating their own sweat, special absorbers are needed, and different ones - such unpleasant substances as methanol, acetaldehyde, ethanol, acetone, isopropanol, and acetic acid evaporate from a sweaty face or a damp palm. This mixture is dominated by acetic acid.

The role of water in a living organism is great. Water is both a medium and a direct participant in physiological and biochemical reactions. With water, various substances formed as a result of metabolism are excreted from the body.

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