Water electrolyte. Pathology of water-electrolyte balance and acid-base imbalance

Water makes up approximately 60% of the body weight of a healthy man (about 42 liters with a body weight of 70 kg). In the female body the total amount of water is about 50%. Normal deviations from average values ​​are approximately within 15%, in both directions. Children have a higher water content in the body than adults; gradually decreases with age.

Intracellular water makes up approximately 30-40% of body weight (about 28 liters in men with a body weight of 70 kg), being the main component of the intracellular space. Extracellular water makes up approximately 20% of body weight (about 14 L). Extracellular fluid consists of interstitial water, which also includes water of ligaments and cartilage (about 15-16% of body weight, or 10.5 l), plasma (about 4-5%, or 2.8 l) and lymph and transcellular water (0.5-1% of body weight), usually not actively participating in metabolic processes (cerebrospinal fluid, intra-articular fluid and the contents of the gastrointestinal tract).

Aqueous media of the body and osmolarity. The osmotic pressure of a solution can be expressed as the hydrostatic pressure that must be applied to a solution to keep it in volumetric equilibrium with a simple solvent when the solution and solvent are separated by a membrane permeable only to the solvent. Osmotic pressure is determined by the number of particles dissolved in water and does not depend on their mass, size and valence.

The osmolarity of a solution, expressed in milliosmoles (mOsm), can be determined by the number of millimoles (but not milliequivalents) of salts dissolved in 1 liter of water, plus the number of undissociated substances (glucose, urea) or weakly dissociated substances (protein). Osmolarity is determined using an osmometer.

The osmolarity of normal plasma is a fairly constant value and is equal to 285-295 mOsm. Of the total osmolarity, only 2 mOsm is due to proteins dissolved in the plasma. Thus, the main component of plasma, ensuring its osmolarity, is sodium and chlorine ions dissolved in it (about 140 and 100 mOsm, respectively).

It is believed that the intracellular and extracellular molar concentrations should be the same, despite qualitative differences in the ionic composition inside the cell and in the extracellular space.

In accordance with the International System (SI), the amount of substances in a solution is usually expressed in millimoles per 1 liter (mmol/l). The concept of “osmolarity”, adopted in foreign and domestic literature, is equivalent to the concept of “molarity”, or “molar concentration”. “Meq” units are used when they want to reflect the electrical relationships in a solution; The unit "mmol" is used to express molar concentration, i.e. the total number of particles in a solution, regardless of whether they carry an electrical charge or are neutral; The units "mOsm" are useful for showing the osmotic strength of a solution. Essentially, the concepts of “mOsm” and “mmol” for biological solutions are identical.

Electrolyte composition of the human body. Sodium is predominantly a cation in extracellular fluid. Chloride and bicarbonate are the anionic electrolyte group of the extracellular space. In the cellular space, the dominant cation is potassium, and the anionic group is represented by phosphates, sulfates, proteins, organic acids and, to a lesser extent, bicarbonates.

Anions located inside the cell are usually polyvalent and do not freely penetrate the cell membrane. The only cellular cation for which the cell membrane is permeable and which is present in the cell in a free state in sufficient quantities is potassium.

The predominant extracellular localization of sodium is due to its relatively low penetrating ability through the cell membrane and a special mechanism for displacing sodium from the cell - the so-called sodium pump. The chlorine anion is also an extracellular component, but its potential penetration through the cell membrane is relatively high; it is not realized mainly because the cell has a fairly constant composition of fixed cellular anions, creating a predominance of negative potential in it, displacing chlorides. Energy for the sodium pump is provided by the hydrolysis of adenosine triphosphate (ATP). The same energy promotes the movement of potassium into the cell.

Elements for monitoring water and electrolyte balance. Normally, a person should consume as much water as is necessary to compensate for its daily loss through the kidneys and extrarenal routes. The optimal daily diuresis is 1400-1600 ml. Under normal temperature conditions and normal air humidity, the body loses from 800 to 1000 ml of water through the skin and respiratory tract - these are the so-called intangible losses. Thus, the total daily excretion of water (urine and perspiration losses) should be 2200-2600 ml. The body is able to partially cover its needs through the use of metabolic water formed in it, the volume of which is about 150-220 ml. A person’s normal balanced daily need for water is from 1000 to 2500 ml and depends on body weight, age, gender and other circumstances. In surgical and intensive care practice, there are three options for determining diuresis: collecting daily urine (in the absence of complications and in mild patients), determining diuresis every 8 hours (in patients receiving infusion therapy of any type during the day) and determining hourly diuresis (in patients with severe water-electrolyte balance disorder, those in shock and suspected renal failure). Satisfactory diuresis for a seriously ill patient, ensuring the electrolyte balance of the body and complete removal of waste, should be 60 ml/h (1500 ± 500 ml/day).

Oliguria is considered to be diuresis less than 25-30 ml/h (less than 500 ml/day). Currently, oliguria is divided into prerenal, renal and postrenal. The first occurs as a result of a block of renal vessels or inadequate blood circulation, the second is associated with parenchymal renal failure and the third with a violation of the outflow of urine from the kidneys.

Clinical signs of water imbalance. If vomiting or diarrhea is frequent, significant fluid and electrolyte imbalance should be suspected. Thirst indicates that the patient has a reduced volume of water in the extracellular space relative to the salt content in it. A patient with true thirst is able to quickly eliminate water deficiency. Loss of clean water is possible in patients who cannot drink on their own (coma, etc.), as well as in patients who are sharply limited in drinking without appropriate intravenous compensation. Loss also occurs with profuse sweating (high temperature), diarrhea and osmotic diuresis (high level glucose in diabetic coma, use of mannitol or urea).

Dryness in the armpits and groin areas is an important symptom of water loss and indicates that its deficiency in the body is at least 1500 ml.

A decrease in tissue and skin turgor is considered as an indicator of a decrease in the volume of interstitial fluid and the body’s need for the introduction of saline solutions (sodium requirement). The tongue under normal conditions has a single, more or less pronounced median longitudinal groove. With dehydration, additional grooves appear parallel to the median.

Body weight, which changes over short periods of time (for example, after 1-2 hours), is an indicator of changes in extracellular fluid. However, the data for determining body weight should be interpreted only in conjunction with other indicators.

Changes in blood pressure and pulse are observed only with a significant loss of water from the body and are most associated with changes in blood volume. Tachycardia is a fairly early sign of decreased blood volume.

Edema always reflects an increase in interstitial fluid volume and indicates that the total amount of sodium in the body is increased. However, edema is not always a highly sensitive indicator of sodium balance, since the distribution of water between the vascular and interstitial spaces is normally due to the high protein gradient between these environments. The appearance of a barely noticeable pressure pit in the area of ​​the anterior surface of the leg with normal protein balance indicates that the body has an excess of at least 400 mmol of sodium, i.e., more than 2.5 liters of interstitial fluid.

Thirst, oliguria and hypernatremia are the main signs of water deficiency in the body.

Hypohydration is accompanied by a decrease in central venous pressure, which in some cases becomes negative. In clinical practice, normal CVP figures are considered to be 60-120 mmH2O. Art. With water overload (overhydration), CVP indicators can significantly exceed these figures. However, excessive use of crystalloid solutions can sometimes be accompanied by water overload of the interstitial space (including interstitial pulmonary edema) without a significant increase in central venous pressure.

Loss of fluid and its pathological movement in the body. External losses of fluid and electrolytes can occur with polyuria, diarrhea, excessive sweating, as well as with profuse vomiting, through various surgical drains and fistulas, or from the surface of wounds and skin burns. Internal movement of fluid is possible with the development of edema in injured and infected areas, but it is mainly due to changes in the osmolarity of fluid media - accumulation of fluid in the pleural and abdominal cavities with pleurisy and peritonitis, blood loss in the tissue with extensive fractures, movement of plasma into injured tissue with crush syndrome , burns or wound area.

A special type of internal movement of fluid is the formation of so-called transcellular pools in the gastrointestinal tract (intestinal obstruction, intestinal infarction, severe postoperative paresis).

The area of ​​the human body where fluid temporarily moves is usually called the “third space” (the first two spaces are the cellular and extracellular water sectors). Such fluid movement, as a rule, does not cause significant changes in body weight. Internal sequestration of fluid develops within 36-48 hours after surgery or after the onset of the disease and coincides with the maximum of metabolic and endocrine changes in the body. Then the process begins to slowly regress.

Disorder of water and electrolyte balance. Dehydration. There are three main types of dehydration: water depletion, acute dehydration and chronic dehydration.

Dehydration due to primary loss of water (water exhaustion) occurs as a result of intense loss by the body of pure water or liquid with a low salt content, i.e. hypotonic, for example with fever and shortness of breath, with prolonged artificial ventilation of the lungs through a tracheostomy without appropriate humidification of the respiratory mixture , with profuse pathological sweating during fever, with elementary limitation of water intake in patients in coma and critical conditions, as well as as a result of the separation of large quantities of weakly concentrated urine in diabetes insipidus. Clinically characterized by a severe general condition, oliguria (in the absence of diabetes insipidus), increasing hyperthermia, azotemia, disorientation, turning into coma, and sometimes convulsions. Thirst appears when water loss reaches 2% of body weight.

Laboratory tests reveal an increase in the concentration of electrolytes in the plasma and an increase in plasma osmolarity. Plasma sodium concentration rises to 160 mmol/l or more. Hematocrit also increases.

Treatment consists of administering water in the form of an isotonic (5%) glucose solution. When treating all types of water and electrolyte balance disorders using various solutions, they are administered only intravenously.

Acute dehydration as a result of loss of extracellular fluid occurs with acute pyloric obstruction, small bowel fistula, ulcerative colitis, as well as with high small bowel obstruction and other conditions. All symptoms of dehydration, prostration and coma are observed, initial oliguria is replaced by anuria, hypotension progresses, and hypovolemic shock develops.

Laboratory tests determine signs of some blood thickening, especially in the later stages. Plasma volume decreases slightly, plasma protein content, hematocrit and, in some cases, plasma potassium content increase; more often, however, hypokalemia quickly develops. If the patient does not receive special infusion treatment, the sodium content in plasma remains normal. With the loss of a large amount of gastric juice (for example, with repeated vomiting), a decrease in plasma chloride levels is observed with a compensatory increase in bicarbonate content and the inevitable development of metabolic alkalosis.

Lost fluid must be replaced quickly. The basis of transfused solutions should be isotonic saline solutions. When there is a compensatory excess of HC0 3 in the plasma (alkalosis), an isotonic glucose solution with the addition of proteins (albumin or protein) is considered the ideal replacement solution. If the cause of dehydration was diarrhea or small intestinal fistula, then, obviously, the content of HCO 3 in the plasma will be low or close to normal and the fluid for replacement should consist of 2/3 of isotonic sodium chloride solution and 1/3 of 4.5% solution sodium bicarbonate. Add to the therapy the introduction of a 1% solution of CO, up to 8 g of potassium (only after restoration of diuresis) and an isotonic glucose solution of 500 ml every 6-8 hours.

Chronic dehydration with loss of electrolytes (chronic electrolyte deficiency) occurs as a result of the transition of acute dehydration with loss of electrolytes into the chronic phase and is characterized by general dilution hypotension of extracellular fluid and plasma. Clinically characterized by oliguria, general weakness, and sometimes increased body temperature. There is almost never thirst. Low sodium content in the blood with a normal or slightly elevated hematocrit is determined in the laboratory. Plasma potassium and chloride levels tend to decrease, especially with prolonged loss of electrolytes and water, for example from the gastrointestinal tract.

Treatment using hypertonic sodium chloride solutions is aimed at eliminating the deficiency of extracellular fluid electrolytes, eliminating extracellular fluid hypotension, and restoring plasma and interstitial fluid osmolarity. Sodium bicarbonate is prescribed only for metabolic acidosis. After restoring plasma osmolarity, a 1% solution of KS1 is administered up to 2-5 g/day.

Extracellular salt hypertension due to salt overload occurs as a result of excessive introduction of salt or protein solutions into the body during water deficiency. It most often develops in patients with tube or tube feeding who are in an inadequate or unconscious state. Hemodynamics remain undisturbed for a long time, diuresis remains normal, in some cases moderate polyuria (hyperosmolarity) is possible. High blood sodium levels with sustained normal diuresis, decreased hematocrit, and increased crystalloid levels are observed. The relative density of urine is normal or slightly increased.

Treatment consists of limiting the amount of salt administered and administering additional water orally (if possible) or parenterally in the form of a 5% glucose solution while reducing the volume of tube or tube feeding.

Primary excess water (water intoxication) becomes possible with the erroneous introduction of excess amounts of water into the body (in the form of an isotonic glucose solution) under conditions of limited diuresis, as well as with excessive administration of water through the mouth or with repeated irrigation of the large intestine. Patients develop drowsiness, general weakness, decreased diuresis, and in later stages coma and convulsions occur. Hyponatremia and hypoosmolarity of plasma are determined in the laboratory, but natriuresis remains normal for a long time. It is generally accepted that when the sodium content decreases to 135 mmol/l in the plasma, there is a moderate excess of water relative to electrolytes. The main danger of water intoxication is swelling and edema of the brain and subsequent hypoosmolar coma.

Treatment begins with complete cessation of water therapy. In case of water intoxication without a deficiency of total sodium in the body, forced diuresis is prescribed with the help of saluretics. In the absence of pulmonary edema and normal central venous pressure, a 3% NaCl solution is administered up to 300 ml.

Pathology of electrolyte metabolism. Hyponatremia (plasma sodium content below 135 mmol/l). 1. Severe diseases that occur with delayed diuresis (cancer processes, chronic infection, decompensated heart defects with ascites and edema, liver disease, chronic starvation).

2. Post-traumatic and postoperative conditions (trauma of the bone skeleton and soft tissues, burns, postoperative sequestration of fluids).

3. Non-renal sodium loss (repeated vomiting, diarrhea, formation of a “third space” in acute intestinal obstruction, small intestinal fistulas, profuse sweating).

4. Uncontrolled use of diuretics.

Since hyponatremia is almost always a condition secondary to the main pathological process, there is no clear treatment for it. Hyponatremia caused by diarrhea, repeated vomiting, enteric fistula, acute intestinal obstruction, postoperative fluid sequestration, as well as forced diuresis, should be treated using sodium-containing solutions and, in particular, isotonic sodium chloride solution; in case of hyponatremia, which has developed in conditions of decompensated heart disease, the introduction of additional sodium into the body is inappropriate.

Hypernatremia (plasma sodium content above 150 mmol/l). 1. Dehydration due to water depletion. An excess of every 3 mmol/L sodium in plasma over 145 mmol/L means a deficiency of 1 L of extracellular water K.

2. Salt overload of the body.

3. Diabetes insipidus.

Hypokalemia (potassium content below 3.5 mmol/l).

1. Loss of gastrointestinal fluid followed by metabolic alkalosis. The concomitant loss of chlorides worsens metabolic alkalosis.

2. Long-term treatment with osmotic diuretics or saluretics (mannitol, urea, furosemide).

3. Stressful conditions with increased adrenal activity.

4. Limitation of potassium intake in the postoperative and post-traumatic periods in combination with sodium retention in the body (iatrogenic hypokalemia).

For hypokalemia, a potassium chloride solution is administered, the concentration of which should not exceed 40 mmol/l. 1 g of potassium chloride, from which a solution for intravenous administration is prepared, contains 13.6 mmol of potassium. Daily therapeutic dose - 60-120 mmol; Large doses are also used according to indications.

Hyperkalemia (potassium content above 5.5 mmol/l).

1. Acute or chronic renal failure.

2. Acute dehydration.

3. Extensive injuries, burns or major operations.

4. Severe metabolic acidosis and shock.

A potassium level of 7 mmol/l poses a serious threat to the patient’s life due to the risk of cardiac arrest due to hyperkalemia.

In case of hyperkalemia, the following sequence of measures is possible and advisable.

1. Lasix IV (from 240 to 1000 mg). A daily diuresis of 1 liter is considered satisfactory (with normal relative density of urine).

2. 10% intravenous glucose solution (about 1 l) with insulin (1 unit per 4 g of glucose).

3. To eliminate acidosis - about 40-50 mmol of sodium bicarbonate (about 3.5 g) in 200 ml of 5% glucose solution; if there is no effect, another 100 mmol is administered.

4. IV calcium gluconate to reduce the effect of hyperkalemia on the heart.

5. If there is no effect from conservative measures, hemodialysis is indicated.

Hypercalcemia (plasma calcium level greater than 11 mg%, or greater than 2.75 mmol/L, on multiple studies) usually occurs with hyperparathyroidism or when cancer has metastasized to bone. Special treatment.

Hypocalcemia (plasma calcium level below 8.5%, or less than 2.1 mmol/l) is observed with hypoparathyroidism, hypoproteinemia, acute and chronic renal failure, with hypoxic acidosis, acute pancreatitis, as well as with magnesium deficiency in the body. Treatment is intravenous administration of calcium supplements.

Hypochloremia (plasma chlorides below 98 mmol/l).

1. Plasmodilution with an increase in the volume of extracellular space, accompanied by hyponatremia in patients with severe diseases, with water retention in the body. In some cases, hemodialysis with ultrafiltration is indicated.

2. Loss of chlorides through the stomach with repeated vomiting, as well as with intense loss of salts at other levels without adequate compensation. Usually combined with hyponatremia and hypokalemia. Treatment is the introduction of chlorine-containing salts, mainly KCl.

3. Uncontrolled diuretic therapy. Combined with hyponatremia. Treatment is cessation of diuretic therapy and salt replacement.

4. Hypokalemic metabolic alkalosis. Treatment is intravenous administration of KCl solutions.

Hyperchloremia (plasma chlorides above 110 mmol/l) is observed with water depletion, diabetes insipidus and brainstem damage (combined with hypernatremia), as well as after ureterosigmostomy due to increased reabsorption of chlorine in the colon. Special treatment.

Basic physical and chemical concepts:

Osmolarity– a unit of concentration of a substance, reflecting its content in one liter of solvent.

Osmolality– a unit of concentration of a substance, reflecting its content in one kilogram of solvent.

Equivalence– an indicator used in clinical practice to reflect the concentration of substances in dissociated form. Equal to the number of millimoles multiplied by the valency.

Osmotic pressure- the pressure that must be applied to stop the movement of water through a semi-permeable membrane along a concentration gradient.

In the adult human body, water makes up 60% of body weight and is distributed in three main sectors: intracellular, extracellular and intercellular (intestinal mucus, serous fluid, cerebrospinal fluid). The extracellular space includes the intravascular and interstitial compartments. The capacity of the extracellular space is 20% of body weight.

Regulation of the volumes of water sectors is carried out according to the laws of osmosis, where the main role is played by the sodium ion, and the concentration of urea and glucose is also important. Normal blood plasma osmolarity is 282 –295 mOsm/ l. It is calculated according to the formula:

P osm = 2  Na +  +2  TO +  +  Glucose +  urea

The above formula reflects the so-called calculated osmolarity, regulated through the content of the listed components and the amount of water as a solvent.

The term measured osmolarity reflects the actual value determined by the osmometer device. Thus, if the measured osmolarity exceeds the calculated one, then unaccounted for osmotically active substances, such as dextran, ethyl alcohol, methanol, etc., circulate in the blood plasma.

The main ion in extracellular fluid is sodium. Normal concentration in plasma 135-145 mmol/l. 70% of the body's total sodium is intensively involved in metabolic processes and 30% is bound in bone tissue. Most cell membranes are impermeable to sodium. Its gradient is maintained by active removal from cells via Na/K ATPase

In the kidneys, 70% of total sodium is reabsorbed in the proximal tubule and another 5% can be reabsorbed in the distal tubule under the influence of aldosterone.

Normally, the volume of fluid entering the body is equal to the volume of fluid released from it. Daily fluid exchange is 2 - 2.5 liters (Table 1).

Table 1. Approximate daily fluid balance

Admission		Selection
path	Quantity (ml)	path	Quantity (ml)
Taking liquids
		Perspiration
Metabolism
Total	2000 - 2500	Total	2000 - 2500

Water losses increase significantly during hyperthermia (10 ml/kg for each degree above 37 0 C), tachypnea (10 ml/kg at RR  20), and mechanical breathing without humidification.

DISHYDRIA

Pathophysiology of water metabolism disorders.

Violations can be associated with a lack of fluid (dehydration) or with its excess (overhydration). In turn, each of the above disorders can be isotonic (with normal plasma osmolarity), hypotonic (when plasma osmolarity is reduced) and hypertonic (plasma osmolarity significantly exceeds the permissible normal limits).

Isotonic dehydration - there is both a water deficiency and a salt deficiency. Plasma osmolarity is normal (270-295 mOsm/L). The extracellular space suffers, it is reduced by hypovolemia. It is observed in patients with losses from the gastrointestinal tract (vomiting, diarrhea, fistulas), blood loss, peritonitis and burn disease, polyuria, in case of uncontrolled use of diuretics.

Hypertensive dehydration is a condition characterized by absolute or predominant fluid deficiency with increased plasma osmolarity. Na > 150 mmol/l, plasma osmolarity > 290 mOsm/l. It is observed with insufficient water intake (inadequate tube feeding - 100 ml of water should be administered for every 100 kcal), gastrointestinal diseases, loss of hypotonic fluid - pneumonia, tracheobronchitis, fever, tracheostomy, polyuria, osmodiuresis in diabetes insipidus.

Hypotonic dehydration - there is a water deficiency with a predominant loss of electrolytes. The extracellular space is reduced, and the cells are oversaturated with water. Na<13О ммоль/л, осмолярность плазмы < 275мосм/л. Наблюдается при состояниях, связанных с потерей солей (болезнь Аддисона, применение диуретиков, слабительных, осмодиурез, диета, бедная натрием), при введении избыточного количества инфузионных растворов, не содержащих электролиты (глюкоза, коллоиды).

Water shortage. Water shortages can be caused by either insufficient supply or excessive losses. Lack of intake is quite rare in clinical practice.

Reasons for increasing water losses:

1. Diabetes insipidus

Central

Nephrogenic

2. Excessive sweating

3. Profuse diarrhea

4. Hyperventilation

In this case, it is not pure water that is lost, but hypotonic fluid. An increase in the osmolarity of the extracellular fluid causes intracellular water to move into the vessels, however, this does not completely compensate for the hyperosmolarity, which increases the content of antidiuretic hormone (ADH). Since such dehydration is partially compensated from the intracellular sector, clinical signs will be mild. If the cause is not renal loss, the urine becomes concentrated.

Central diabetes insipidus often occurs after neurosurgery and TBI. The reason is damage to the pituitary gland or hypothalamus, which is expressed in a decrease in the synthesis of ADH. The disease is characterized by polydipsia and polyuria without glugosuria. Urine osmolarity is lower than plasma osmolarity.

Nephrogenic diabetes insipidus develops, most often, secondary to chronic kidney disease and sometimes as a side effect of nephrotoxic drugs (amphotericin B, lithium, demeclocycline, mannitol). The reason lies in a decrease in the sensitivity of renal tubular receptors to vasopressin. The clinical manifestations of the disease are the same, and the diagnosis is verified by the absence of a decrease in the rate of diuresis when ADH is administered.

Sodium deficiency.

The causes of sodium deficiency can be either excessive excretion or insufficient intake. Excretion, in turn, can occur through the kidneys, intestines and skin.

Causes of sodium deficiency:

1. Loss through the kidneys

Polyuric phase of acute renal failure;

Use of diuretics

Mineralocorticoid deficiency

Osmodiuresis (for example, in diabetes mellitus)

2. Loss through the skin

Dermatitis;

Cystic fibrosis.

3. Loss through the intestines

Intestinal obstruction, peritonitis.

4. Loss of fluid rich in salts, compensated by salt-free solutions (profuse diarrhea compensated by 5% glucose solution).

Sodium can be lost in hypo- or isotonic fluids. In both cases, there is a decrease in the volume of extracellular space, which leads to irritation of volume receptors and the release of aldosterone. Increased sodium retention causes an increase in the secretion of protons into the lumen of the nephron tubule and the reabsorption of bicarbonate ions (see renal mechanisms of acid-base regulation), i.e. causes metabolic alkalosis.

When sodium is lost, its concentration in plasma does not reflect the total content in the body, since it depends on the accompanying loss of water. So, if it is lost in the hypotonic fluid, the plasma concentration will be higher than normal; if it is lost in combination with water retention, it will be lower. Loss of equal amounts of sodium and water will not affect its plasma levels. Diagnosis of the predominance of water and sodium losses is presented in Table 2.

Table 2. Diagnosis of predominant water or sodium losses

If water loss predominates, the osmolarity of the extracellular fluid increases, which causes the transition of water from cells to the interstitium and vessels. Therefore, clinical signs will be less clearly expressed.

The most typical case is the loss of sodium in isotonic fluid (isotonic dehydration). Depending on the degree of dehydration of the extracellular sector, three degrees of dehydration are distinguished in the clinical picture (Table 3).

Table 3: Clinical diagnosis of the degree of dehydration.

Excess water.

Excess water is associated with impaired excretion, i.e. renal failure. The ability of healthy kidneys to excrete water is 20 ml/hour, therefore, if their function is not impaired, excess water due to excess intake is practically excluded. Clinical signs of water intoxication are caused primarily by cerebral edema. The danger of its occurrence arises when the sodium concentration approaches 120 mmol/l.

Biological chemistry Lelevich Vladimir Valeryanovich

Chapter 29. Water-electrolyte metabolism

Distribution of fluid in the body

To perform specific functions, cells require a stable living environment, including a stable supply of nutrients and the constant elimination of waste products. The basis of the internal environment of the body is made up of liquids. They account for 60–65% of body weight. All body fluids are distributed between two main fluid compartments: intracellular and extracellular.

Intracellular fluid is the fluid contained inside cells. In adults, intracellular fluid accounts for 2/3 of all fluid, or 30–40% of body weight. Extracellular fluid is fluid found outside of cells. In adults, extracellular fluid accounts for 1/3 of the total fluid, or 20–25% of body weight.

Extracellular fluid is divided into several types:

1. Interstitial fluid is the fluid surrounding cells. Lymph is an interstitial fluid.

2. Intravascular fluid – fluid located inside the vascular bed.

3. Transcellular fluid contained in specialized body cavities. Transcellular fluid includes cerebrospinal fluid, pericardial fluid, pleural fluid, synovial fluid, intraocular fluid, and digestive juices.

Composition of liquids

All liquids consist of water and substances dissolved in it.

Water is the main component of the human body. In adult men, water makes up 60% and in women – 55% of body weight.

Factors influencing the amount of water in the body include:

1. Age. As a rule, the amount of water in the body decreases with age. In a newborn, the amount of water is 70% of body weight, at the age of 6 - 12 months - 60%, in an elderly person - 45 - 55%. A decrease in the amount of water with age occurs due to a decrease in muscle mass.

2. Fat cells. They contain little water, so the amount of water in the body decreases with increasing fat content.

3. Gender The female body has relatively less water because it contains relatively more fat.

Solutes

Body fluids contain two types of solutes—nonelectrolytes and electrolytes.

1. Non-electrolytes. Substances that do not dissociate in solution and are measured by mass (for example, mg per 100 ml). Clinically important non-electrolytes include glucose, urea, creatinine, and bilirubin.

2. Electrolytes. Substances that dissociate in solution into cations and anions and their content is measured in milliequivalents per liter [meq/l]. The electrolyte composition of liquids is presented in the table.

Table 29.1. Main electrolytes of body fluid compartments (average values ​​shown)

Electrolyte content, meq/l	Extracellular fluid		Intracellular fluid
	plasma	interstitial
Na+	140	140	10
K+	4	4	150
Ca2+	5	2,5	0
Cl-	105	115	2
PO 4 3-	2	2	35
HCO 3 -	27	30	10

The main extracellular cations are Na +, Ca 2+, and intracellular K +, Mg 2+. Outside the cell, the predominant anions are Cl - and HCO 3 -, and the main anion of the cell is PO 4 3-. Intravascular and interstitial fluids have the same composition, since the endothelium of the capillaries is freely permeable to ions and water.

The difference in the composition of extracellular and intracellular fluids is due to:

1. Impermeability of the cell membrane to ions;

2. The functioning of transport systems and ion channels.

Characteristics of liquids

In addition to composition, the general characteristics (parameters) of liquids are important. These include: volume, osmolality and pH.

Volume of liquids.

The volume of liquid depends on the amount of water that is currently present in a particular space. However, water passes passively, mainly due to Na +.

The volume of adult body fluids is:

1. Intracellular fluid – 27 l

2. Extracellular fluid – 15 l

Interstitial fluid – 11 l

Plasma – 3 l

Transcellular fluid – 1 l.

Water, biological role, water exchange

Water in the body exists in three states:

1. Constitutional (strongly bound) water, part of the structure of proteins, fats, carbohydrates.

2. Loosely bound water diffusion layers and outer hydration shells of biomolecules.

3. Free, mobile water is the medium in which electrolytes and nielectrolytes dissolve.

There is a state of dynamic equilibrium between bound and free water. So the synthesis of 1 g of glycogen or protein requires 3 g of H 2 O, which passes from the free state to the bound state.

Water in the body performs the following biological functions:

1. Solvent of biological molecules.

2. Metabolic – participation in biochemical reactions (hydrolysis, hydration, dehydration, etc.).

3. Structural – providing a structural layer between polar groups in biological membranes.

4. Mechanical – helps maintain intracellular pressure and cell shape (turgor).

5. Heat balance regulator (storage, distribution, heat release).

6. Transport – ensuring the transfer of dissolved substances.

Water exchange

The daily water requirement for an adult is about 40 ml per 1 kg of body weight or about 2500 ml. The residence time of a water molecule in the body of an adult is about 15 days, in the body of an infant – up to 5 days. Normally, there is a constant balance between water intake and loss (Fig. 29.1).

Rice. 29.1 Water balance (external water exchange) of the body.

Note. Water loss through the skin consists of:

1. insensible water loss - evaporation from the skin surface at a rate of 6 ml/kg body weight/hour. Newborns have a higher evaporation rate. This water loss does not contain electrolytes.

2. noticeable water loss - sweating, which loses water and electrolytes.

Regulation of extracellular fluid volume

Significant fluctuations in the volume of the interstitial part of the extracellular fluid can be observed without a pronounced effect on body functions. The vascular portion of the extracellular fluid is less resistant to change and must be carefully monitored to ensure that the tissue is adequately supplied with nutrients while continuously removing waste products. The volume of extracellular fluid depends on the amount of sodium in the body, therefore the regulation of the volume of extracellular fluid is associated with the regulation of sodium metabolism. Aldosterone plays a central role in this regulation.

Aldosterone acts on the main cells of the collecting ducts, i.e., the distal part of the renal tubules - the area in which about 90% of filtered sodium is reabsorbed. Aldosterone binds to intracellular receptors, stimulates gene transcription and protein synthesis that open sodium channels in the apical membrane. As a result, an increased amount of sodium enters the chief cells and activates the Na + , K + - ATPase of the basolateral membrane. Increased transport of K + into the cell in exchange for Na + leads to increased secretion of K + through potassium channels into the lumen of the tubule.

The role of the renin-angiotensin system

The renin-angiotensin system plays an important role in the regulation of osmolality and extracellular fluid volume.

System activation

With a decrease in blood pressure in the afferent arterioles of the kidneys, if the sodium content in the distal tubules decreases, the granular cells of the juxtaglomerular apparatus of the kidneys synthesize and secrete into the blood the proteolytic enzyme renin. Further activation of the system is shown in Fig. 29.2.

Rice. 29.2. Activation of the renin-angiotensin system.

Atrial natriuretic factor

Atrial natriuretic factor (ANF) is synthesized by the atria (mainly the right one). PNP is a peptide and is released in response to any events that lead to an increase in cardiac volume or pressure accumulation. PNF, unlike angiotensin II and aldosterone, reduces vascular volume and blood pressure.

The hormone has the following biological effects:

1. Increases kidney excretion of sodium and water (due to increased filtration).

2. Reduces renin synthesis and aldosterone release.

3. Reduces ADH release.

4. Causes direct vasodilation.

Disturbances of water-electrolyte metabolism and acid-base balance

Dehydration.

Dehydration (dehydration, water deficiency) leads to a decrease in the volume of extracellular fluid—hypovolemia.

Develops due to:

1. Abnormal loss of fluid through the skin, kidneys, and gastrointestinal tract.

2. Reduced water flow.

3. Movement of liquid into the third space.

A marked decrease in extracellular fluid volume can lead to hypovolemic shock. Prolonged hypovemia can cause the development of renal failure.

There are 3 types of dehydration:

1. Isotonic – uniform loss of Na + and H 2 O.

2. Hypertonic – lack of water.

3. Hypotonic – lack of fluid with a predominance of Na+ deficiency.

Depending on the type of fluid loss, dehydration is accompanied by a decrease or increase in osmolality, COR, Na + and K + levels.

Edema is one of the most severe disorders of water and electrolyte metabolism. Edema is the excess accumulation of fluid in interstitial spaces, such as the legs or pulmonary interstitium. In this case, swelling of the underlying substance of the connective tissue occurs. Edema fluid is always formed from blood plasma, which under pathological conditions is not able to retain water.

Edema develops due to the action of factors:

1. Decrease in the concentration of albumin in the blood plasma.

2. Increased levels of ADH and aldosterone causing water and sodium retention.

3. Increased capillary permeability.

4. Increase in capillary hydrostatic blood pressure.

5. Excess or redistribution of sodium in the body.

6. Impaired blood circulation (for example, heart failure).

Acid-base imbalance

Disturbances occur when the mechanisms for maintaining the cortical index are unable to prevent changes. Two extreme conditions can be observed. Acidosis is an increase in the concentration of hydrogen ions or loss of bases leading to a decrease in pH. Alkalosis is an increase in the concentration of bases or a decrease in the concentration of hydrogen ions causing an increase in pH.

Changes in blood pH below 7.0 or above 8.8 cause the death of the body.

Three forms of pathological conditions lead to disruption of the cortical index:

1. Impaired removal of carbon dioxide by the lungs.

2. Excessive production of acidic foods by tissues.

3. Impaired excretion of bases in urine and feces.

From the point of view of developmental mechanisms, there are several types of CBF disorders.

Respiratory acidosis – caused by an increase in pCO 2 above 40 mm. Hg st due to hypoventilation in diseases of the lungs, central nervous system, and heart.

Respiratory alkalosis – characterized by a decrease in pCO 2 less than 40 mm. Hg Art., is the result of increased alveolar ventilation and is observed with mental agitation, lung diseases (pneumonia).

Metabolic acidosis is a consequence of a primary decrease in bicarbonate in the blood plasma, which is observed with the accumulation of non-volatile acids (ketoacidosis, lactic acidosis), loss of bases (diarrhea), and decreased excretion of acids by the kidneys.

Metabolic alkalosis - occurs when the level of bicarbonate in the blood plasma increases and is observed with the loss of acidic stomach contents through vomiting, the use of diuretics, and Cushing's syndrome.

Mineral components of tissues, biological functions

Most of the elements found in nature are found in the human body.

From the point of view of quantitative content in the body, they can be divided into 3 groups:

1. Microelements - content in the body is more than 10–2%. These include sodium, potassium, calcium, chloride, magnesium, phosphorus.

2. Microelements – content in the body from 10–2% to 10–5%. These include zinc, molybdenum, iodine, copper, etc.

3. Ultramicroelements – content in the body is less than 10–5%, for example silver, aluminum, etc.

In cells, minerals are found in the form of ions.

Basic biological functions

1. Structural – participate in the formation of the spatial structure of biopolymers and other substances.

2. Cofactor – participation in the formation of active centers of enzymes.

3. Osmotic – maintaining osmolarity and volume of fluids.

4. Bioelectric – generation of membrane potential.

5. Regulatory – inhibition or activation of enzymes.

6. Transport – participation in the transfer of oxygen and electrons.

Sodium, biological role, metabolism, regulation

Biological role:

1. Maintaining water balance and osmolality of extracellular fluid;

2. Maintaining osmotic pressure, extracellular fluid volume;

3. Regulation of acid-base balance;

4. Maintaining neuromuscular excitability;

5. Transmission of nerve impulses;

6. Secondary active transport of substances through biological membranes.

The human body contains about 100 g of sodium, which is distributed mainly in the extracellular fluid. Sodium comes from food in an amount of 4–5 g per day and is absorbed in the proximal small intestine. T? (half-exchange time) for adults 11–13 days. Sodium is excreted from the body in urine (3.3 g/day), then (0.9 g/day), and feces (0.1 g/day).

Regulation of exchange

The main regulation of metabolism is carried out at the level of the kidneys. They are responsible for the excretion of excess sodium and contribute to its preservation in case of deficiency.

Renal excretion:

1. enhance: angiotensin-II, aldosterone;

2. reduces PNF.

Potassium, biological role, metabolism, regulation

Biological role:

1. participation in maintaining osmotic pressure;

2. participation in maintaining acid-base balance;

3. conduction of nerve impulses;

4. maintaining neuromuscular excitation;

5. contraction of muscles, cells;

6. activation of enzymes.

Potassium is the main intracellular cation. The human body contains 140 g of potassium. About 3–4 g of potassium is supplied daily with food, which is absorbed in the proximal small intestine. T? potassium – about 30 days. Excreted in urine (3 g/day), feces (0.4 g/day), then (0.1 g/day).

Regulation of exchange

Despite the low content of K + in plasma, its concentration is very strictly regulated. The entry of K+ into cells is enhanced by adrenaline, aldosterone, insulin, and acidosis. The overall K+ balance is regulated at the kidney level. Aldosterone enhances the release of K + by stimulating secretion through potassium channels. With hypokalemia, the regulatory capabilities of the kidneys are limited.

Calcium, biological role, metabolism, regulation

Biological role:

1. structure of bone tissue, teeth;

2. muscle contraction;

3. excitability of the nervous system;

4. intracellular hormone mediator;

5. blood clotting;

6. activation of enzymes (trypsin, succinate dehydrogenase);

7. secretory activity of glandular cells.

The body contains about 1 kg of calcium: in the bones - about 1 kg, in soft tissues, mainly extracellularly - about 14 g. 1 g per day is supplied with food, and 0.3 g / day is absorbed. T? for calcium contained in the body is about 6 years, for calcium in skeletal bones - 20 years.

Blood plasma contains calcium in two forms:

1. non-diffusible, bound to proteins (albumin), biologically inactive – 40%.

2. diffusible, consisting of 2 fractions:

Ionized (free) – 50%;

Complex, associated with anions: phosphate, citrate, carbonate – 10%.

All forms of calcium are in dynamic, reversible equilibrium. Only ionized calcium has physiological activity. Calcium is excreted from the body: with feces – 0.7 g/day; with urine 0.2 g/day; with sweat 0.03 g/day.

Regulation of exchange

In the regulation of Ca 2+ metabolism, 3 factors are important:

1. Parathyroid hormone - increases the release of calcium from bone tissue, stimulates reabsorption in the kidneys, and by activating the conversion of vitamin D into its form D 3 increases the absorption of calcium in the intestines.

2. Calcitonin – reduces the release of Ca 2+ from bone tissue.

3. The active form of vitamin D - vitamin D 3 stimulates the absorption of calcium in the intestines. Ultimately, the action of parathyroid hormone and vitamin D is aimed at increasing the concentration of Ca2+ in the extracellular fluid, including in plasma, and the action of calcitonin is aimed at decreasing this concentration.

Phosphorus, biological role, metabolism, regulation

Biological role:

1. formation (together with calcium) of bone tissue structure;

2. structure of DNA, RNA, phospholipids, coenzymes;

3. formation of macroergs;

4. phosphorylation (activation) of substrates;

5. maintaining acid-base balance;

6. regulation of metabolism (phosphorylation, dephosphorylation of proteins, enzymes).

The body contains 650 g of phosphorus, of which 8.5% is in the skeleton, 14% in soft tissue cells, and 1% in extracellular fluid. Approximately 2 g per day is supplied, of which up to 70% is absorbed. T? calcium of soft tissues – 20 days, skeleton – 4 years. Phosphorus is excreted: in urine - 1.5 g/day, in feces - 0.5 g/day, in sweat - about 1 mg/day.

Regulation of exchange

Parathyroid hormone enhances the release of phosphorus from bone tissue and its excretion in the urine, and also increases absorption in the intestine. Typically, the concentrations of calcium and phosphorus in the blood plasma change in the opposite way. However, not always. In hyperparathyroidism, the levels of both increase, and in childhood rickets, the concentrations of both decrease.

Essential microelements

Essential microelements are microelements without which the body cannot grow, develop and complete its natural life cycle. Essential elements include: iron, copper, zinc, manganese, chromium, selenium, molybdenum, iodine, cobalt. The basic biochemical processes in which they participate have been established. Characteristics of vital microelements are given in Table 29.2.

Table 29.2. Essential microelements, brief description.

Micro element	Content in the body (on average)	Main functions
Copper	100 mg	Component of oxidases (cytochrome oxidase), participation in the synthesis of hemoglobin, collagen, immune processes.
Iron	4.5 g	Component of heme-containing enzymes and proteins (Hb, Mb, etc.).
Iodine	15 mg	Necessary for the synthesis of thyroid hormones.
Cobalt	1.5 mg	Component of vitamin B 12.
Chromium	15 mg	Participates in the binding of insulin to cell membrane receptors, forms a complex with insulin and stimulates the manifestation of its activity.
Manganese	15 mg	Cofactor and activator of many enzymes (pyruvate kinase, decarboxylase, superoxide dismutase), participation in the synthesis of glycoproteins and proteoglycans, antioxidant effect.
Molybdenum	10 mg	Cofactor and activator of oxidases (xanthine oxidase, serine oxidase).
Selenium	15 mg	Part of selenoproteins, glutathione peroxidase.
Zinc	1.5 g	Cofactor for enzymes (LDH, carbonic anhydrase, RNA and DNA polymerases).

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Regulation of water-salt metabolism , like most physiological regulations, it includes afferent, central and efferent components. The afferent link is represented by a mass of receptor apparatus of the vascular bed, tissues and organs that perceive shifts in osmotic pressure, volume of liquids and their ionic composition. As a result, an integrated picture of the state of water-salt balance in the body is created in the central nervous system. Thus, with an increase in the concentration of electrolytes and a decrease in the volume of circulating fluid (hypovolemia), a feeling of thirst appears, and with an increase in the volume of circulating fluid (hypervolemia), it decreases. The consequence of the central analysis is a change in drinking and eating behavior, a restructuring of the gastrointestinal tract and excretory system (primarily kidney function), implemented through efferent links of regulation. The latter are represented by nervous and, to a greater extent, hormonal influences. An increase in the volume of circulating fluid due to increased water content in the blood (hydremia) can be compensatory, occurring, for example, after massive blood loss. Hydremia with autohemodilution is one of the mechanisms for restoring the correspondence of the volume of circulating fluid to the capacity of the vascular bed. Pathological hydremia is a consequence of impaired water-salt metabolism, for example, in renal failure, etc. A healthy person may develop short-term physiological hydremia after taking large amounts of liquid.

In addition to the permanent exchange of water between the body and the environment, the exchange of water between the intracellular, extracellular sectors and blood plasma is important. It should be noted that the mechanisms of water-electrolyte exchange between sectors cannot be reduced only to physicochemical processes, since the distribution of water and electrolytes is also related to the functioning of cell membranes. The most dynamic is the interstitial sector, which primarily affects the loss, accumulation and redistribution of water and shifts in electrolyte balance. Important factors influencing the distribution of water between the vascular and interstitial sectors are the degree of permeability of the vascular wall, as well as the ratio and interaction of hydrodynamic pressures of the sectors. In plasma, the protein content is 65-80 g/l, and in the interstitial sector only 4 g/l. This creates a constant difference in colloid-osmotic pressure between the sectors, ensuring the retention of water in the vascular bed. The role of hydrodynamic and oncotic factors in the exchange of water between sectors was shown back in 1896. American physiologist E. Starling: the transition of the liquid part of the blood into the interstitial space and back is due to the fact that in the arterial capillary bed the effective hydrostatic pressure is higher than the effective oncotic pressure, and in the venous capillary - vice versa.

Humoral regulation of water and electrolyte balance in the body is carried out by the following hormones:

Antidiuretic hormone (ADH, vasopressin) acts on the collecting ducts and distal tubules of the kidneys, increasing water reabsorption;
- natriuretic hormone (atrial natriuretic factor, ANF, atriopeptin), dilates afferent arterioles in the kidneys, which increases renal blood flow, filtration rate and Na+ excretion; inhibits the release of renin, aldosterone and ADH;
- the renin-angiotensin-aldosterone system stimulates the reabsorption of Na+ in the kidneys, which causes NaCl retention in the body and increases the osmotic pressure of the plasma, which determines the delay in fluid excretion.

- parathyroid hormone increases the absorption of potassium by the kidneys and intestines and the excretion of phosphate and increases the reabsorption of calcium.

The sodium content in the body is regulated mainly by the kidneys under the control of the central nervous system through specific natrioreceptors. responding to changes in sodium content in body fluids, as well as volume receptors and osmoreceptors, responding to changes in the volume of circulating fluid and osmotic pressure of extracellular fluid, respectively. The sodium content in the body is controlled by the renin-angiotensin system, aldosterone, and natriuretic factors. With a decrease in water content in the body and an increase in the osmotic pressure of the blood, the secretion of vasopressin (antidiuretic hormone) increases, which causes an increase in the reabsorption of water in the renal tubules. An increase in sodium retention by the kidneys is caused by aldosterone, and an increase in sodium excretion is caused by natriuretic hormones, or natriuretic factors (atriopeptides, prostaglandins, ouabain-like substance).

The state of water-salt metabolism largely determines the content of Cl- ions in the extracellular fluid. Chlorine ions are excreted from the body mainly through urine, gastric juice, and sweat. The amount of excreted sodium chloride depends on the diet, active sodium reabsorption, the state of the renal tubular apparatus, and the acid-base state. The exchange of chlorine in the body is passively associated with the exchange of sodium and is regulated by the same neurohumoral factors. The exchange of chlorides is closely related to the exchange of water: a decrease in edema, resorption of transudate, repeated vomiting, increased sweating, etc. are accompanied by an increase in the excretion of chlorine ions from the body.

The balance of potassium in the body is maintained in two ways:
changes in the distribution of potassium between intra- and extracellular compartments, regulation of renal and extrarenal excretion of potassium ions.
The distribution of intracellular potassium in relation to extracellular potassium is maintained primarily by Na-K-ATPase, which is a structural component of the membranes of all cells of the body. Potassium absorption by cells against the concentration gradient is initiated by insulin, catecholamines, and aldosterone. It is known that acidosis promotes the release of potassium from cells, while alkalosis promotes the movement of potassium into cells.

The fraction of potassium excreted by the kidneys usually accounts for approximately 10-15% of the total filterable plasma potassium. The retention in the body or the excretion of potassium by the kidney is determined by the direction of potassium transport in the connecting tubule and collecting duct of the renal cortex. When the content of potassium in food is high, these structures secrete it, but when it is low, there is no secretion of potassium. In addition to the kidneys, potassium is excreted through the gastrointestinal tract and through sweating. At the usual level of daily potassium intake (50-100 mmol/day), approximately 10% is excreted in the stool.

The main regulators of calcium and phosphorus metabolism in the body are vitamin D, parathyroid hormone and calcitonin. Vitamin D (as a result of transformations in the liver, vitamin D3 is formed, in the kidneys - calcitriol) increases the absorption of calcium in the digestive tract and the transport of calcium and phosphorus to the bones. Parathyroid hormone is released when the level of calcium in the blood serum decreases, but a high level of calcium inhibits the formation of parathyroid hormone. Parathyroid hormone helps increase calcium levels and decrease phosphorus concentrations in the blood serum. Calcium is resorbed from the bones, its absorption in the digestive tract also increases, and phosphorus is removed from the body in the urine. Parathyroid hormone is also necessary for the formation of the active form of vitamin D in the kidneys. An increase in serum calcium levels promotes the production of calcitonin. In contrast to parathyroid hormone, it causes the accumulation of calcium in the bones and reduces its level in the blood serum, reducing the formation of the active form of vitamin D in the kidneys. Increases the excretion of phosphorus in the urine and reduces its level in the blood serum.

Water-salt metabolism is the totality of processes of water and electrolytes entering the body, their distribution in the internal environment and excretion from the body.

Water-salt metabolism in the human body

Water-salt metabolism is called a set of processes of water and electrolytes entering the body, their distribution in the internal environment and excretion from the body.

A healthy person maintains equal volumes of water released from the body and entered into it per day, which is called water balance body. You can also consider the balance of electrolytes - sodium, potassium, calcium, etc. The average water balance of a healthy person at rest is shown in table. 12.1, and the balance of electrolytes in table. 12.2.

Average values ​​of water balance parameters of the human body

Table 12.1. Average values ​​of water balance parameters of the human body (ml/day)
Water consumption and production		Water release
Drinking and liquid food	1200	With urine	1500
Solid food	1100	With then	500
Endogenous "water of oxidation"	300	With exhaled air	400
		With feces	100
Total Receipt	2500	Total Allocation	2500
Internal cycle of gastrointestinal fluids (ml/day)
Secretion		Reabsorption
Saliva	1500
Gastric juice	2500
Bile	500
Pancreas juice	700
Intestinal juice	3000
Total	8200		8100
Total 8200 - 8100 = water in stool 100 ml

Average daily metabolic balance of certain substances in humans

Table 12.2 Average daily metabolic balance of certain substances in humans
Substances	Admission		Selection
	food	metabolism	urine	feces	sweat and air
Sodium (mmol)	155		150	2,5	2,5
Potassium (mmol)				5,0
Chloride (mmol)	155		150	2,5	2,5
Nitrogen (g)
Acids (meq)
non-volatile
volatile	14000				14000

Under various disturbing influences(changes in environmental temperature, different levels of physical activity, changes in nutritional patterns) individual balance indicators may change, but the balance itself remains unchanged.

Under pathological conditions, imbalances occur with a predominance of either retention or loss of water.

Body water

Water is the most important inorganic component of the body, ensuring the connection between the external and internal environments and the transport of substances between cells and organs.

Being a solvent of organic and inorganic substances, water represents the main environment for the development of metabolic processes. It is part of various systems of organic substances.

Each gram of glycogen, for example, contains 1.5 ml of water, each gram of protein contains 3 ml of water.

With its participation, such structures as cell membranes, transport particles of blood, macromolecular and supramolecular formations are formed. In the process of metabolism and hydrogen oxidation , separated from the substrate, is formed, endogenous "water of oxidation"

Moreover, its amount depends on the type of decaying substrates and the level of metabolism.

• So, at rest during oxidation:
• 100 g of fat produces more than 100 ml of water,
• 100 g protein - about 40 ml water,

100 g carbohydrates - 55 ml water.

An increase in catabolism and energy metabolism leads to a sharp increase in the endogenous water produced.

In particular, an increase in protein consumption and, accordingly, their final conversion into urea, which is removed from the body in the urine, leads to the absolute need for an increase in water loss in the kidneys, which requires an increased intake into the body.

When eating predominantly carbohydrate, fatty foods and a small intake of NaCl into the body, the body's need for water intake is less.

For a healthy adult, the daily water requirement ranges from 1 to 3 liters.

The total amount of water in a person's body ranges from 44 to 70% of body weight or approximately 38-42 liters.

Its content in different tissues varies from 10% in adipose tissue to 83-90% in the kidneys and blood; with age, the amount of water in the body decreases, as well as with obesity.

Women have lower water content than men.

Body water forms two water spaces:

1. Intracellular (2/3 of total water).

2. Extracellular (1/3 of total water).

3. Under pathological conditions, a third water space appears - body cavity water: abdominal, pleural, etc.

The extracellular water space includes two sectors:

1. Intravascular water sector, i.e. blood plasma, the volume of which is about 4-5% of body weight.

2. Interstitial water sector, containing 1/4 of all body water (15% of body weight) and being the most mobile, changing volume with excess or lack of water in the body.

All body water is renewed in about a month, and the extracellular water space is renewed in a week.

Overhydration of the body

Excessive intake and formation of water with inadequately small excretion from the body leads to the accumulation of water and this shift in water balance is called overhydration.

With overhydration, water accumulates mainly in the interstitial water sector.

Water intoxication

A significant degree of overhydration manifests itself water intoxication .

At the same time, in the interstitial water sector the osmotic pressure becomes lower than inside the cells, they absorb water, swell and the osmotic pressure in them also becomes reduced.

As a result of the increased sensitivity of nerve cells to a decrease in osmolarity, water intoxication can be accompanied by excitation of nerve centers and muscle cramps.

Dehydration of the body

Insufficient supply and formation of water or excessively large release of it lead to a decrease in water spaces, mainly in the interstitial sector, which is called dehydration.

This is accompanied by thickening of the blood, deterioration of its rheological properties and impaired hemodynamics.

A lack of water in the body of 20% of body weight leads to death.

Regulation of the body's water balance

The water balance regulation system provides two main homeostatic processes:

firstly, maintaining a constant total volume of fluid in the body and,

secondly, the optimal distribution of water between water spaces and sectors of the body.

Factors maintaining water homeostasis include osmotic and oncotic pressure of fluids in aqueous spaces, hydrostatic and hydrodynamic blood pressure, permeability of histohematic barriers and other membranes, active transport of electrolytes and non-electrolytes, neuro-endocrine mechanisms regulating the activity of the kidneys and other excretory organs, as well as drinking behavior and thirst.

Water-salt metabolism

The body's water balance is closely related to electrolyte metabolism. The total concentration of mineral and other ions creates a certain amount of osmotic pressure.

The concentration of individual mineral ions determines the functional state of excitable and non-excitable tissues, as well as the state of permeability of biological membranes, which is why it is customary to say O water-electrolyte(or saline)exchange.

Water-electrolyte metabolism

Since mineral ions are not synthesized in the body, they must be supplied to the body through food and drink. To maintain electrolyte balance and, accordingly, vital activity, the body should receive per day approximately 130 mmol of sodium and chlorine, 75 mmol of potassium, 26 mmol of phosphorus, 20 mmol of calcium and other elements.

The role of electrolytes in the functioning of the body

For homeostasis electrolytes require the interaction of several processes: entry into the body, redistribution and deposition in cells and their microenvironment, excretion from the body.

Entry into the body depends on the composition and properties of food and water, the characteristics of their absorption in the gastrointestinal tract and the state of the enteric barrier. However, despite wide fluctuations in the quantity and composition of nutrients and water, the water-salt balance in a healthy body is steadily maintained due to changes in excretion through the excretory organs. The kidneys play a major role in this homeostatic regulation.

Regulation of water-salt metabolism

Regulation of water-salt metabolism, like most physiological regulations, includes afferent, central and efferent links.

The afferent link is represented by a mass of receptor apparatus of the vascular bed, tissues and organs that perceive shifts in osmotic pressure, volume of liquids and their ionic composition. As a result, an integrated picture of the state of water-salt balance in the body is created in the central nervous system. The consequence of the central analysis is a change in drinking and eating behavior, a restructuring of the gastrointestinal tract and excretory system (primarily kidney function), implemented through efferent regulatory links. The latter are represented by nervous and, to a greater extent, hormonal influences.