Homeostasis is one of the main properties of living things to maintain relative dynamic
constancy of the internal environment i.e. chemical composition, osmotic
pressure, stability of basic physiological functions.
This is the body’s ability to maintain a relative constancy of the internal environment (blood, lymph, intercellular fluid).
The human body adapts to constantly changing environmental conditions, but the internal environment remains constant and its indicators fluctuate within very narrow limits. Therefore, a person can live in different environmental conditions. Some physiological parameters are regulated especially carefully and subtly, for example, body temperature, blood pressure, glucose, gases, salts, calcium ions in the blood, acid-base balance, blood volume, its osmotic pressure, appetite, and many others. Regulation is carried out on the principle of negative feedback between receptors that detect changes in these indicators and control systems. Thus, a decrease in one of the parameters is captured by the corresponding receptor, from which impulses are sent to one or another structure of the brain, at the command of which the autonomic nervous system turns on complex mechanisms for equalizing the changes that have occurred. The brain uses two main systems to maintain homeostasis: autonomic and endocrine.
One of the most important physicochemical parameters of the internal environment is acid-base balance .
The quantitative reaction of the blood characterizes the hydrogen index (pH) - the negative decimal logarithm of the concentration of hydrogen and ions.
Most solutions in the body are buffer solutions, in which the pH does not change when small amounts of a strong acid or alkali are added to them.
Tissue fluid, blood, urine and other liquids are buffer solutions.
The pH indicator of body fluids clearly demonstrates how much Na, Mg, Ca, K is absorbed. These 4 components regulate the acidity of the body. If the acidity is high, substances begin to be borrowed from other organs and cavities. To carry out all the functions of living structures at all levels from molecular systems to organs, a slightly alkaline environment (pH 7.4) is required.
Even the slightest deviation from the normal value can cause pathology.
pH changes: to acidic – acidosis
to alkaline – alkalosis
A shift of 0.1 can lead to disruption of the environment, and a shift of 0.3 can be life-threatening.
pH levels of blood and other internal fluids. Metabolism and metabolites.
Standards for internal fluids:
Arterial blood 7.35 – 7.45
Venous blood 7.26 – 7.36
Lymph 7.35 – 7.40
Intercellular fluid 7.26 – 7.38
Urine pH 5-7 (acidity changes depending on food intake and physical activity. Alkalinity of urine - plant foods; acidity of urine - meat, physical activity).
Deviations and norms:
- Acidic liquid reaction
Fasting, increased body temperature, diabetes, impaired renal function, heavy physical work.
- Alkaline reaction
Inflammation of the bladder, diet poor in meat products, excess mineral water, blood in the urine.
Any organism is characterized by a set of indicators by which the physicochemical properties of the internal environment are assessed, except for pH, which is estimated by the inverse decimal logarithm p and p, as well as stroke volume of the heart, heart rate, blood pressure, blood flow speed, peripheral vascular resistance, minute volume of respiration etc. The totality of these indicators characterizes the functional level of the body.
Metabolism is a set of chemical reactions occurring in living cells and
providing the body with substances and energy for basic metabolism.
Metabolites are products of intracellular metabolism that are subject to final elimination from the body.
The acid-base state is one of the most important physical and chemical parameters of the internal environment of the body. In the body of a healthy person, acids are constantly formed daily during the metabolic process - about 20,000 mmol of carbonic acid (H 2 C0 3) and 80 mmol of strong acids, but the concentration of H + fluctuates in a relatively narrow range. Normally, the pH of the extracellular fluid is 7.35-7.45 (45-35 nmol/l), and the pH of the intracellular fluid is on average 6.9. At the same time, it should be noted that the H+ concentration inside the cell is heterogeneous: it is different in the organelles of the same cell.
H+ are reactive to such an extent that even a short-term change in their concentration in the cell can significantly affect the activity of enzyme systems and physiological processes; however, normally, buffer systems instantly turn on, protecting the cell from unfavorable pH fluctuations. The buffer system can bind, or, conversely, release H+ immediately in response to changes in the acidity of the intracellular fluid. Buffer systems also operate at the level of the body as a whole, but ultimately the regulation of the body’s pH is determined by the functioning of the lungs and kidneys.
So, what is the acid-base state (syn.: acid-base balance; acid-base state; acid-base balance; acid-base homeostasis)? This is the relative constancy of the pH value of the internal environment of the body, due to the combined action of buffer and some physiological systems of the body.
Acid-base balance is the relative constancy of the hydrogen index (pH) of the internal country of the body, due to the combined action of buffer and some physiological systems, which determines the usefulness of metabolic transformations in the cells of the body (Big Medical Encyclopedia, vol. 10, p. 336).
The ratio of hydrogen and hydroxyl ions in the internal environment of the body depends on:
1) enzyme activity and intensity of redox reactions;
2) processes of hydrolysis and protein synthesis, glycolysis and oxidation of carbohydrates and fats;
3) sensitivity of receptors to mediators;
4) membrane permeability;
5) the ability of hemoglobin to bind oxygen and release it to tissues;
6) physicochemical characteristics of colloids and intercellular structures: the degree of their dispersity, hydrophilia, adsorption ability;
7) functions of various organs and systems.
The ratio of H+ and OH- in biological media depends on the content of acids (proton donors) and buffer bases (proton acceptors) in body fluids. The active reaction of the medium is assessed by one of the ions (H+ or OH-), most often by H+. The H+ content in the body depends on their formation during the metabolism of proteins, fats and carbohydrates, as well as their entry into the body or removal from it in the form of non-volatile acids or carbon dioxide.
The pH value, which characterizes the state of the CBS, is one of the most “hard” blood parameters and varies in humans within very narrow limits: from 7.35 to 7.45. A pH shift of 0.1 beyond the specified limits causes pronounced disturbances in the respiratory, cardiovascular system, etc., a pH decrease of 0.3 causes acidotic coma, and a pH shift of 0.4 is often incompatible with life.
The exchange of acids and bases in the body is closely related to the exchange of water and electrolytes. All these types of metabolism are united by the law of electrical neutrality, isosmolarity and homeosgatic physiological mechanisms.
The total amount of plasma cations is 155 mmol/l (Na+ -142 mmol/l; K+ - 5 mmol/l; Ca2+ - 2.5 mmol/l; Mg2+ - 0.5 mmol/l; other elements - 1.5 mmol/l ) and the same amount of anions is contained (103 mmol/l - weak base Cl-; 27 mmol/l - strong base HC03-; 7.5-9 mmol/l - protein anions; 1.5 mmol/l - phosphate anions; 0. 5 mmol/l - sulfatanions; 5 mmol/l - organic acids). Since the H+ content in plasma does not exceed 40x106 mmol/l, and the main buffer bases of plasma HCO3- and protein anions are about 42 mmol/l, the blood is considered a well-buffered medium and has a slightly alkaline reaction.
Protein and HCO3- anions are closely related to the metabolism of electrolytes and CBS. In this regard, the correct interpretation of changes in their concentration is of decisive importance for assessing the processes occurring in the exchange of electrolytes, water and H+. CBS is supported by blood and tissue buffer systems and physiological regulatory mechanisms, which involve the lungs, kidneys, liver, and gastrointestinal tract.
Physicochemical homeostatic mechanisms
Physicochemical homeostatic mechanisms include buffer systems of blood and tissues and, in particular, the carbonate buffer system. When the body is exposed to disturbing factors (acids, alkalis), the maintenance of acid-base homeostasis is ensured, first of all, by a carbonate buffer system consisting of weak carbonic acid (H 2 CO3) and the sodium salt of its anion (NaHCO3) in a ratio of 1:20. When this buffer comes into contact with acids, the latter are neutralized by the alkaline component of the buffer with the formation of weak carbonic acid: NaHC03 + HCl > NaCl + H2C03
Carbonic acid dissociates into CO2 and H20. The resulting CO2 excites the respiratory center, and excess carbon dioxide is removed from the blood with exhaled air. The carbonate buffer is also able to neutralize excess bases by binding with carbonic acid to form NaHCO3 and its subsequent excretion by the kidneys:
NaOH + H2C03 > NaHCO + H20.
The specific gravity of the carbonate buffer is small and amounts to 7-9% of the total buffer capacity of the blood, however, this buffer occupies a central place in its importance in the blood buffer system, since it is the first to come into contact with disturbing factors and is closely connected with other buffer systems and physiological regulatory mechanisms. Therefore, the carbonate buffer system is a sensitive indicator of CBS, so the determination of its components is widely used to diagnose CBS disorders.
The second buffer system of the blood plasma is a phosphate buffer formed by monobasic (weak acids) and dibasic (strong bases) phosphate salts: NaH2P04 and Na2HP04 in a ratio of 1:4. Phosphate buffer acts similarly to carbonate buffer. The stabilizing role of phosphate buffer in the blood is insignificant; it plays a much greater role in the renal regulation of acid-base homeostasis, as well as in the regulation of the active reaction of some tissues. The phosphate buffer in the blood plays an important role in maintaining the ACR and the reproduction of the bicarbonate buffer:
H2CO3 + Na2HPO4 > NaHC03 + NaH2PO 4 i.e. excess H2C03 is eliminated, and the concentration of NaHC03 increases, and the ratio of H2C03/NaHC03 remains constant at 1:20.
The third blood buffer system is proteins, the buffering properties of which are determined by their amphotericity. They can dissociate to form both H+ and OH-. However, the buffering capacity of plasma proteins compared to bicarbonates is small. The largest buffering capacity of blood (up to 75%) is hemoglobin. Histidine, which is part of hemoglobin, contains both acidic (COOH) and basic (NH2) groups.
The buffering properties of hemoglobin are due to the possibility of interaction of acids with the potassium salt of hemoglobin to form an equivalent amount of the corresponding potassium salt and free hemoglobin, which has the properties of a very weak organic acid. Large amounts of H+ can be bound in this way. The ability to bind H+ in Hb salts is more pronounced than in oxyhemoglobin salts (HbO2). In other words, hemoglobin is a weaker organic acid than oxyhemoglobin. In this regard, during the dissociation of HbO, an additional amount of bases (Hb salts) appear in the tissue capillaries on O2 and Hb, capable of binding carbon dioxide, counteracting the decrease in pH, and vice versa, the oxygenation of Hb leads to the displacement of H2CO3 from bicarbonate. These mechanisms operate during the conversion of arterial blood into venous blood and vice versa, as well as when pCO2 changes.
Hemoglobin is able to bind carbon dioxide using free amino groups, forming carbohemoglobin
R-NH2 + CO2 - R-NHCOOH
Thus, NHC03 in the carbonate buffer system during the “aggression” of acids is compensated by alkaline proteins, phosphates and hemoglobin salts.
The exchange of Cl and HCO3 between erythrocytes and plasma is extremely important in maintaining CBS. With an increase in the concentration of carbon dioxide in the plasma, the concentration of Cl in it decreases, since chlorine ions pass into red blood cells. The main source of Cl in plasma is NaCl. As the concentration of H2CO3 increases, the bond between Na+ and Cl- breaks and their separation occurs, with chlorine ions entering the erythrocytes, and sodium ions remaining in the plasma, since the erythrocyte membrane is practically impermeable to them. At the same time, the resulting excess Na+ combines with excess HCO3-, forming sodium bicarbonate and replenishing its loss during blood acidification and thus maintaining a constant blood pH.
A decrease in pCO2 in the blood causes the opposite process: chlorine ions leave the red blood cells and combine with excess sodium ions released from NaHC03, which prevents alkalization of the blood.
An important role in maintaining CBS belongs to tissue buffer systems - they contain carbonate and phosphate buffer systems. However, a special role is played by tissue proteins, which have the ability to bind very large quantities of acids and alkalis.
An equally important role in the regulation of CBS is played by homeostatic metabolic processes occurring in tissues, especially in the liver, kidneys and muscles. Organic acids, for example, can be oxidized to form volatile acids that are easily released from the body (mainly in the form of carbon dioxide), or combine with products of protein metabolism, completely or partially losing their acidic properties.
Lactic acid, formed in large quantities during intense muscular work, can be resynthesized into glycogen, and ketone bodies into higher fatty acids, and then into fats, etc. Inorganic acids can be neutralized by potassium and sodium salts, released when amino acids are deaminated with ammonia to form ammonium salts.
Alkalies can be neutralized by lactate, which is intensively formed from glycogen when the pH of tissues shifts. CBS is maintained due to the dissolution of strong acids and alkalis in lipids, their binding by various organic substances into non-dissociable and insoluble salts, and the exchange of ions between the cells of various tissues and the blood.
Ultimately, the determining link in maintaining acid-base homeostasis is cellular metabolism, since the transmembrane flow of anions and cations and their distribution between extra- and intracellular sectors is the result of cell activity and is subject to the needs of this activity.
Physiological homeostatic mechanisms
An equally important role in maintaining acid-base homeostasis is played by physiological homeostatic mechanisms, among which the leading role belongs to the lungs and kidney.” Organic acids formed during the metabolic process, or acids that enter the body from the outside, thanks to the buffer systems of the blood, displace carbon dioxide from its compounds with bases, and the resulting excess CO2 is excreted by the lungs.
Carbon dioxide diffuses approximately 20 times more intensely than oxygen. This process is facilitated by two mechanisms:
the transition of hemoglobin to oxyhemoglobin (oxyhemoglobin, as a stronger acid, displaces CO2 from the blood);
The action of pulmonary carbonic anhydrase carbonic anhydrase
n2co3 - co2+ n2o.
The amount of carbon dioxide removed from the body by the lungs depends on the frequency and amplitude of breathing and is determined by the carbon dioxide content in the body.
The participation of the kidneys in maintaining CBS is determined mainly by their acid-excreting function. Under normal conditions, the kidneys produce urine whose pH ranges from 5.0 to 7.0. The pH value of urine can reach 4.5, which indicates an 800-fold excess of H+ in it compared to blood plasma. Acidification of urine in the proximal and distal renal tubules is a consequence of H+ secretion (acidogenesis). An important role in this process is played by carbonic anhydrase of the epithelium of the renal tubules. This enzyme accelerates the achievement of equilibrium between the slow reaction of hydration and dehydration of carbonic acid:
carbonic anhydrase
n2co3 - n2o + co2
As pH decreases, the rate of uncatalyzed H2CO3 > H2 + HCO3- increases. Thanks to acidogenesis, acidic components of the phosphate buffer (H + + HP04 2- > H2PO4-) and weak organic acids (lactic, citric, β-hydroxybutyric, etc.) are removed from the body. The release of H+ by the epithelium of the renal tubules occurs against an electrochemical gradient with energy costs, and at the same time reabsorption of an equivalent amount of Na+ occurs (a decrease in Na+ reabsorption is accompanied by a decrease in acidogenesis). Na+ reabsorbed due to acidogenesis forms sodium bicarbonate in the blood together with HCO3- secreted by the epithelium of the renal tubules
Na + + HC03 - > NaHC03
H+ ions secreted by the epithelium of the renal tubules interact with the anions of buffer compounds. Acidogenesis ensures the release of predominantly anions of carbonate and phosphate buffers and anions of weak organic acids.
Anions of strong organic and inorganic acids (CI-, S0 4 2-) are removed from the body by the kidneys due to ammoniogenesis, which ensures the excretion of acids and protects the urine pH from decreasing below the critical level of the distal tubules and collecting ducts. NH3, formed in the epithelium of the renal tubules during the deamination of glutamine (60%) and other amino acids (40%), entering the lumen of the tubules, combines with H+ formed during acidogenesis. Thus, ammonia binds hydrogen ions and removes the anions of strong acids in the form of ammonium salts.
Ammoniogenesis is closely related to acidogenesis, therefore the concentration of ammonium in the urine is directly dependent on the concentration of H+ in it: acidification of the blood, accompanied by a decrease in the pH of the tubular fluid, promotes the diffusion of ammonia from the cells. Ammonium excretion is also determined by the rate of its production and the rate of urine flow.
Chlorides play an important role in the regulation of acid excretion by the kidneys - an increase in HCO3- reabsorption is accompanied by an increase in chloride reabsorption. The chlorine ion passively follows the sodium cation. The change in chloride transport is a consequence of the primary change in the secretion of H+ ions and the reabsorption of HCO3 and is due to the need to maintain the electrical neutrality of tubular urine.
In addition to acidosis and ammoniogenesis, a significant role in the preservation of Na+ during blood acidification belongs to the secretion of potassium. Potassium, released from cells when the blood pH decreases, is intensively excreted by the epithelium of the renal tubules while simultaneously increasing the reabsorption of Na+ - this affects the regulatory effect of mineralocorticoids: aldosterone and deoxycorticosterone. Normally, the kidneys secrete predominantly acidic metabolic products, but with an increased intake of bases into the body, the urine reaction becomes more alkaline due to the increased secretion of bicarbonate and basic phosphate.
The gastrointestinal tract plays an important role in the excretory regulation of CBS. Hydrochloric acid is formed in the stomach: H+ is secreted by the gastric epithelium, and CI- comes from the blood. In exchange for chlorides, bicarbonate enters the blood during gastric secretion, but alkalization of the blood does not occur, since the CI- gastric juice is reabsorbed into the blood. In the intestine, the epithelium of the intestinal mucosa secretes alkaline juice rich in bicarbonates. In this case, H+ passes into the blood in the form of HCl. A short-term shift in the reaction is immediately balanced by the reabsorption of NaHC03 in the intestine. The intestinal tract, in contrast to the kidneys, which concentrate and release mainly K+ and monovalent cations from the body, concentrates and removes divalent alkaline ions from the body. With an acidic diet, the release of mainly Ca2+ and Mg2+ increases, and with an alkaline diet, the release of all cations increases.
2.Blood buffer systems. The role of buffer systems in maintaining pH homeostasis. Acid-base state. The concept of acidosis and alkalosis.
In the body, acid formation predominates over the formation of basic compounds.
Sources of H+ in the body:
1. volatile acid H2CO3, 10-20 thousand mmol of CO2 per day during the oxidation of proteins, F, U.
2.non-volatile acids per day. 70 mmol:
Phosphoric when breaking down organic phosphates (nucleotides, PL, phosphoproteins)
Sulfuric, hydrochloric during oxidation B
3.org.k-you: milk, ketone bodies, PVC, etc.
The pH is maintained at a slightly alkaline level due to the participation of buffer cells and physiological control (excretory function of the kidneys and respiratory function of the lungs)
Henderson-Hesselbach equation: pH = pKa + log [proton accumulator]/[proton donor].
(Salt) (acid)
Any buffer consists of a conjugate acid-base pair: proton donor + acceptor.
Buffer capacity: depends on the absolute concentrations of the buffer components.
Bicarbonate.
10% buffer blood capacity.
At normal blood pH (7.4), the concentration of bicarbonate ions HCO 3 in the blood plasma exceeds the concentration of CO 2 by approximately 20 times. The bicarbonate buffer system functions as an effective regulator in the pH range of 7.4.
The mechanism of action of this system is that when relatively large quantities of acidic products are released into the blood, hydrogen ions H + interact with bicarbonate ions HCO 3 –, which leads to the formation of weakly dissociating carbonic acid H 2 CO 3. A subsequent decrease in the concentration of H 2 CO 3 is achieved as a result of the accelerated release of CO 2 through the lungs as a result of their hyperventilation (recall that the concentration of H 2 CO 3 in the blood plasma is determined by the pressure of CO 2 in the alveolar gas mixture).
If the amount of bases in the blood increases, then they interact with weak carbonic acid to form bicarbonate ions and water. In this case, no noticeable shifts in the pH value occur. In addition, to maintain a normal ratio between the components of the buffer system, in this case, physiological mechanisms for regulating acid-base balance are activated: a certain amount of CO 2 is retained in the blood plasma as a result of hypoventilation of the lungs.
NaHCO3 + H+ → Na+ + H2CO3
Reabs. in the kidneys ↓carbonic anhydrase
↓increased ventilation of the lungs
Phosphate is a conjugated acid-base pair consisting of an H 2 PO 4 – ion (proton donor) and an HPO 4 2 – ion (proton acceptor):
The phosphate buffer system makes up only 1% of the buffer capacity of the blood. In extracellular fluid, including blood, the ratio [HPO 4 2– ]: [H 2 PO 4 – ] is 4:1. The buffering effect of the phosphate system is based on the possibility of binding hydrogen ions with HPO 4 2– ions to form H 2 PO 4 – (H + + + HPO 4 2– -> H 2 PO 4 –), as well as OH – ions with H 2 PO ions 4 – (OH – + + H 2 R O 4 – -> HPO 4 2– + H 2 O). The buffer pair (H 2 PO 4 – –HPO 4 2–) is capable of influencing changes in pH in the range from 6.1 to 7.7 and can provide a certain buffer capacity of the intracellular fluid, the pH value of which is in the range of 6.9–7, 4. In the blood, the maximum capacity of the phosphate buffer appears around the pH value of 7.2.
1 and 2 – output.
Protein is less important for maintaining COR in the blood plasma than other buffer systems. Proteins form a buffer system due to the presence of acid-base groups in the protein molecule: protein–H + (acid, proton donor) and protein (conjugate base, proton acceptor). The protein buffer system of blood plasma is effective in the pH range of 7.2–7.4.
The hemoglobin buffer system is the most powerful buffer system in the blood. It is 9 times more powerful than a bicarbonate buffer; it accounts for 75% of the total buffer capacity of the blood. consists of non-ionized hemoglobin HHb (weak organic acid, proton donor) and potassium salt of hemoglobin KHb (conjugate base, proton acceptor). The oxyhemoglobin buffer system can be considered in the same way. The hemoglobin system and the oxyhemoglobin system are interconvertible systems and exist as a single whole.
Mechanism of action:
In tissues: H2O + CO2 (carbonic anhydrase) -> H2CO3 -> H + + HCO3 - (diffuses into blood plasma)
KNvO2 ->KNv + 4O2
KHb + 2H+ -> HHb + 2K+ (K-hemoglobin neutralizes H+ ions)
In the lungs: HHb + 4O2 -> 2H+ + HbO2
2H+ + HBO2 + 2K+ + 2HCO3- ->KHBO2 + 2H2CO3 (carbonic anhydrase) ->H2O + 2CO2
pH and CO2 concentration affect the release and binding of O2 by nemoglobin - Boron effect.
Increasing the concentration of protons, CO2, promotes the release of O2, and increasing the concentration of O2 stimulates the release of CO2 and protons.
5167 0
The acid-base state (ABS) is one of the very important components of the body’s homeostasis, an indispensable condition for the optimal activity of enzyme catalysts for metabolic processes. During the metabolic process, various acids and bases are formed, and they are also introduced from the outside. Disorders of various organs can lead to disruption of CBS, which in turn causes various pathological changes in the body. In some cases, KOS indicators are a fairly accurate criterion of IT efficiency. Therefore, it is necessary to know the mechanisms of physiological regulation and disorders of CBS, be able to assess their condition and correctly carry out the prevention and correction of disorders.
Diagnostics
The values of the CBS indicators are maintained within narrow limits by physico-chemical reactions and neurohumoral mechanisms of powerful systems:
- buffer (hemoglobin, protein, bicarbonate, etc.)
- functional (lungs, kidneys, liver, gastrointestinal tract).
When the pH changes, the body's buffer systems immediately react, then the functional ones. The maximum compensation of the latter is slower (lungs - about 12-24 hours, kidneys - about a week). Therefore, to assess the CBS, you need to know the qualitative and quantitative changes primarily in buffer systems (especially hemoglobin, which accounts for 73-76% of the total buffer capacity of the blood, and bicarbonate, which is very mobile and reflects the state of other buffer systems). The main indicators of KOS: pHa - current pH, BEa - excess bases, PaCO2 - CO2 tension in arterial blood at a temperature of 38 ° C without air access.
Normal pH values in humans are 7.36-7.44. The limits of pathological deviations compatible with life are 6.8-8.0. A decrease in pH indicates acidemia, and an increase indicates alkalemia. The conditions that lead to them are called acidosis or alkalosis. pH reflects the degree of compensation, but not the essence of CBS shifts.
Normal values are BEa±2.3 mmol/l. In pathology, the value of BEa can vary within ±15 mmol/l. BEA is a metabolic component of CBS; a decrease or increase in it indicates metabolic acidosis or alkalosis, respectively. BE can also change compensatory for respiratory disorders.
The concept of acid-base homeostasis, its main parameters. The role of stabilizing the pH of the internal environment for the body. Functional system for maintaining the constancy of acid-base homeostasis parameters. The importance of maintaining a constant pH in life. The role of external respiration, kidneys and blood buffer systems in pH stabilization.
The concept of pH, the role of constancy of the pH of the internal environment for the implementation of intracellular metabolism.
Acid-base homeostasis
Acid-base balance is one of the most important physical and chemical parameters of the internal environment of the body. The ratio of hydrogen and hydroxyl ions in the internal environment of the body largely determines the activity of enzymes, the direction and intensity of redox reactions, the processes of breakdown and synthesis of protein, glycolysis and oxidation of carbohydrates and fats, the functions of a number of organs, the sensitivity of receptors to mediators, the permeability of membranes and etc. The activity of the reaction of the environment determines the ability of hemoglobin to bind oxygen and release it to tissues. When the reaction of the environment changes, the physicochemical characteristics of cell colloids and intercellular structures change - the degree of their dispersity, hydrophilia, adsorption ability and other important properties.
The ratio of active masses of hydrogen and hydroxyl ions in biological media depends on the content of acids (proton donors) and buffer bases (proton acceptors) in body fluids. It is customary to evaluate the active reaction of the environment by one of the ions (H +) or (OH -), more often by the H + ion. The H+ content in the body is determined, on the one hand, by their direct or indirect formation through carbon dioxide during the metabolism of proteins, fats and carbohydrates, and on the other hand, by their entry into the body or removal from it in the form of non-volatile acids or carbon dioxide. Even relatively small changes in CH + inevitably lead to disruption of physiological processes, and with shifts beyond certain limits, to the death of the organism. In this regard, the pH value, which characterizes the state of acid-base balance, is one of the most “hard” blood parameters and varies within a narrow range in humans - from 7.32 to 7.45. A pH shift of 0.1 beyond the specified limits causes pronounced disturbances in the respiratory, cardiovascular system, etc.; a decrease in pH by 0.3 causes an acidotic coma, and a shift in pH by 0.4 is often incompatible with life.
The exchange of acids and bases in the body is closely related to the exchange of water and electrolytes. All these types of exchange are united by the laws of electroneutrality, isosmolarity and homestatic physiological mechanisms. For plasma, the law of electrical neutrality can be illustrated by the data in Table. 20.
The total amount of plasma cations is 155 mmol/l, of which 142 mmol/l is sodium. The total amount of anions is also 155 mmol/l, of which 103 mmol/l is the weak base C1 - and 27 mmol/l is the share of HCO - 3 (strong base). G. Ruth (1978) believes that HCO - 3 and protein anions (approximately 42 mmol/l) constitute the main buffer bases of plasma. Due to the fact that the concentration of hydrogen ions in plasma is only 40·10 -6 mmol/l, blood is a well-buffered solution and has a slightly alkaline reaction. Protein anions, especially the HCO - 3 ion, are closely related, on the one hand, to the exchange of electrolytes, and on the other, to the acid-base balance, therefore the correct interpretation of changes in their concentration is important for understanding the processes occurring in the exchange of electrolytes, water and H + .
