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The functional abilities of the kidneys affect the condition of the entire human body. Blood purification is carried out in the kidneys by nephrons. Glomerular filtration of the kidneys is important diagnostic value and its rate must be maintained at a constant level. Deviations in the indicator indicate the presence of pathological processes in the body.

The kidneys serve as the main organ excretory system person. Depends on their functional abilities general state health. Through them, the blood is cleansed of toxins.

The purification process is carried out in the glomerular apparatus. It consists of huge amount nephrons, consisting of vascular glomeruli and passing tubules. As a result of passing through the nephrons, the blood is cleared of toxins and passes on.

Important! IN healthy condition human speed glomerular filtration kidney has a certain value, which depends on age and gender and is maintained at a constant level.

The glomerular filtration rate shows how much blood the kidneys can clear in 1 minute. Deviations from the indicator indicate the development of pathology of the urinary system.

The speed of filtration capacity is influenced by the following factors:

The number of nephrons that participate in the process of blood purification. With kidney pathologies, nephrons die and are no longer restored. With a reduced number of nephrons, the kidneys cannot cope with their functions, which leads to the death of even more nephrons.
The volume of blood that flows through the kidneys. The normal value is 600 ml/min. When the volume is exceeded, the load increases.
Vascular pressure level. When it changes, difficulties arise in filtration and its speed decreases.

How to calculate

Glomerular velocity can be calculated in several ways. For this purpose, special formulas are used, with which you can carry out calculations both manually on a calculator and on a computer.

Creatinine clearance serves important indicator kidney functions. According to the Cockcroft-Gold method, a person needs to urinate and drink a glass of water in the morning. After this, the collection of urine samples begins hourly, noting the start and end times of urination. At the same time, a blood test is taken to compare the level of creatinine in urine and serum.

The calculation is carried out using the formula: F1=(u1/p)v1, where:

F1 – glomerular filtration rate;
u1 – amount of creatinine in urine;
p – amount of creatinine in the blood;
v1 - duration of the first urination in minutes.

The second formula is also used:

GFR = ((140 – age, years)*(weight, kg))/(72*blood creatinine)

Interesting to know! For women, the figure is lower and multiplied by 0.85.

The rate of glomerular kidney function is calculated using the Schwartz formula: GFR = k*growth/Scr, where:

K – age coefficient,
SCr is the amount of creatinine in the blood.

Important! The state of kidney health can be assessed correctly using calculation methods only experienced specialist. Independent use calculations may give incorrect results and aggravate the condition.

Norm

GFR depends on several factors. The most important are the age and gender of the person.

Table of norms by gender:

As a person ages, the filtration capacity of the kidneys decreases. After 50 years, the rate drops by about 7 ml/min every 10 years.

In children, norms vary depending on age factor:

Deviations from accepted standards indicate the presence of pathological processes in the urinary system and require additional examination body.

Exceeding the indicator is considered to be a value higher than normal by 40-50 ml/min. This means that the kidneys allow more blood flow due to the increase in the size of the nephron tubules. As a result of this, part useful substances, which must be retained in the blood, are excreted in the urine.

Symptoms of this condition may include feeling thirsty and frequent urge to urination, the appearance of edema. Due to a lack of nutrients, a person feels tired and weak.

The kidney's filtration rate may increase due to an increase in blood volume or flow rate, or due to increased tone vessels. Increasing the filtration rate refers to pathological abnormalities and requires identification exact reason speed violations.

Among the main reasons for the increase in GFR are:

hypertension;
pregnancy;
burns;
protein diet;
diabetes.

Treatment depends on the underlying cause of the decrease in speed and is prescribed by the attending physician.

Demotion

Low renal filtration rate is much more common. A reading below 50 ml/min is considered pathological symptom kidney failure. This means that the kidneys do not fully perform their functions and toxins accumulate in the patient’s body.

In this case, the person experiences pain in the lower back, nausea, weakness, the color of the urine becomes saturated and problems with urination appear. Factors such as a decrease in blood volume due to dehydration, bleeding or blockage of blood vessels, and an increase in pressure can lead to a drop in GFR.

Important! Low filtration rate is dangerous sign and may cause serious consequences. At the first signs of deterioration in kidney function, you should consult a specialist.

In such a situation, treatment is necessary, which depends directly on the cause of the decrease in the indicator. How to increase the filtration rate in a particular case is decided by the attending physician based on general health patient and severity of symptoms.

Diagnostics

The speed of renal glomeruli is the main indicator of renal function. This indicator allows you to identify many pathologies internal organs on early stages. To determine the filtration capacity, blood and urine tests are used.

Based on determining the amount of substances in these samples, calculation formulas are used. The main criteria are the content of creatinine and inulin.

Important role Collecting urine samples plays a role in diagnosis. Failure to follow all rules for collecting samples and preparing for research can lead to distorted results and incorrect diagnosis. To clarify the diagnosis, additional urine and blood tests, as well as hardware examination of the body, can be used.

GFR helps identify the following diseases:

diabetes;
lupus erythematosus;
inflammatory processes;
nephropathy;
ameloidosis of the kidneys;
kidney nephropathy;
renal failure.

The urinary system is responsible for cleansing the body of toxins and harmful substances. The glomerular filtration rate is an important indicator of kidney function and allows us to identify many diseases.

If you have problems with your kidneys, you should consult a specialist and have your body examined. After diagnosis, the doctor will prescribe the necessary treatment.

The structural unit of the kidney is the nephron, which is responsible for the process of filtering blood. The two urinary organs contain about two million nephrons, which are intertwined in groups into small balls. This is the glomerular apparatus (glomerular), in which glomerular filtration of the kidneys occurs.

Important: during the day, from 120 to 200 liters of blood passes through the nephron glomeruli. At the same time, it is in the nephrons that all toxins and breakdown products of proteins, carbohydrates and fats are separated.

The principle of the filtration process

The kidney filtration process is quite simple and straightforward. First, blood enriched with oxygen and other nutrients, enters the kidneys, namely the glomerular apparatus. In the nephrons, which have a kind of “sieve”, toxic substances and other breakdown products are separated from water. After this division, water and useful microelements(glucose, sodium, potassium) are absorbed back. That is, the process of reabsorption occurs. And all toxins continue their movement through the nephron tubules to the renal pyramids and further into pyelocalyceal system. Secondary urine is already formed here, which exits through the ureters, bladder and urethra.

Important: it is worth knowing that if a person’s kidneys are sick, then the nephrons in them slowly die one by one. Thus, the filtering function of the urinary organs gradually decreases. It must be remembered that nephrons, like nerve cells, cannot be restored. And those nephrons that take on double and triple loads, over time, cease to cope with their function and soon fail.

Factors that may influence changes in GFR

The rate of filtration in the glomerular apparatus depends on the following factors:

The rate of plasma transport through the renal glomerular apparatus. That is, it refers to the volume of blood passing through the lumbar arteriole in a certain unit of time. Normally, this figure is 600 ml/min for a person with an average weight of 70 kg.
Pressure indicator in vascular system body. For normal and healthy body more typical high pressure in the vessel bringing in than in the vessel taking out. Otherwise, the filtration process will be difficult and its speed will be reduced.
Number of healthy nephrons. The more the kidney is affected by the pathological condition, the smaller the filtering area becomes. That is, the number of healthy nephrons decreases.

GFR Estimation

To assess the filtration function of the urinary organs, it is necessary to find out the GFR (rate of the filtration process), which is calculated in ml/min. And the work of the urinary organs itself is assessed by the amount of creatinine in the urine collected from the patient. In order to correctly determine the level of creatinine, a daily volume of urine should be collected from the patient.

As for deducing the glomerular filtration rate (GFR), for this it is necessary to collect urine from the patient using a similar method. Normal glomerular apparatus healthy organs pumps up to 120 ml/min. At the same time, it is worth knowing that patients in age group 55+ speed metabolic processes the rate of blood filtration in the kidneys also decreases, which means it decreases. The GFR indicator is the rate of formation of primary urine from the filtrate over a certain unit of time.

Important: normally, kidney filtration in healthy organs occurs at a constant rate and remains unchanged until pathological processes develop in the urinary organs.

Pathologies that determine GFR

Pathological processes that change the glomerular filtration rate of the kidneys downward can be very diverse. In particular, the following pathologies and diseases affect GFR:

Chronic renal failure. In this case, increased concentrations of creatinine and urea will be noted in the urine. That is, the kidneys cannot cope with their filtration function.
Pyelonephritis. This inflammatory-infectious disease primarily affects the nephron tubules. And only then does the GFR decline.
Diabetes. And also with hypertension (high blood pressure), lupus erythematosus, an increased rate of the kidney filtration process is observed.
Hypotension (low blood pressure). And state of shock and heart failure can provoke a decrease in GFR to significant limits.

Help in diagnosing diseases

Measuring GFR makes it possible to identify various diseases And pathological conditions on early stages. At the same time, in order to track the filtration process in the kidneys, the method of introducing inulin into the blood is often used - a special control substance that is excreted through the glomerular apparatus. Inulin is administered continuously during the study to maintain a constant concentration in the blood.

Urine collection for analysis while maintaining inulin levels is carried out four times with an interval of half an hour. But it is worth knowing that this method of analyzing the condition of the kidneys is quite complex and is applicable exclusively for scientific purposes.

GFR can also be assessed by the level of creatinine clearance, which directly depends on the patient’s lean body mass. It is worth knowing here that active men have significantly higher creatinine clearance than women and children. Note that creatinine leaves the body exclusively through the glomerular apparatus. Therefore, if the filtration process in the kidneys is impaired, the concentration of creatinine in the urine increases and is 70% compared to GFR.

Important: when conducting a urine test for creatinine, you need to know that medications can greatly distort the results. Normally, the creatinine level for men is 18-21 mg/kg, and for women 15-18 mg/kg. If the levels are reduced, this may indicate a malfunction of the kidneys.

This method of studying the functioning of the urinary organs is carried out as follows:

In the morning, the patient is asked to drink half a liter of water on an empty stomach. After this, he must urinate every hour to collect portions of the biomaterial into separate containers.
When urinating, the patient must note the time of the beginning and end of the act.
And in the interval between collecting portions of urine, blood is taken from a vein from the patient to determine creatinine clearance. It is calculated using a special formula. The calculation formula looks like this: F1=(u1/p)v1.

Here the following interpretations have meaning:

Fi is glomerular filtration (its rate);
U1 is the content of the control substance in the blood;
Vi – time of the very first urination after drinking water (in minutes)
p is the concentration of creatinine in blood plasma.

Creatinine clearance is calculated using the given formula every hour. In this case, calculations are carried out throughout the day.

This is interesting: normally in men the GFR is 125 liters/min, and in women it is 110 ml/min.

Calculation of GFR in children

To calculate the glomerular filtration rate in children, the Schwartz formula is used. In the first case, little patient On an empty stomach, blood is drawn from a vein. It is necessary to determine the level of creatinine in blood plasma. Against the background of the biomaterial taken, two portions of urine are collected from the baby at an hourly interval. And they also record the duration of the act of urination in minutes or seconds. Calculations using the Schwartz formula make it possible to obtain two GFR values.

For the second method of calculation, the daily volume of urine is collected from a small patient at hourly intervals. Here the volume should be at least 1.5 liters. If, when performing calculations, the result of the glomerular filtration rate is 15 ml/min (that is, greatly reduced), then this indicates renal failure or chronic kidney disease.

Important: GFR may not always fall due to the death of nephrons. Often, the filtration rate may decrease due to kidney disease. inflammatory process. That is why, at the first suspicious symptoms (lower back pain, dark urine, swelling), it is necessary to urgently contact a nephrologist or urologist.

Treatment of kidneys and restoration of filtration rate

If violations of the filtration function of the kidneys are detected, treatment should be prescribed only by a specialist, depending on the root cause that led to the pathology. In most cases, the drugs “Theobromine” and “Eufillin” help improve the situation. They increase diuresis, which leads to normalization of GFR.

Also, during treatment it is necessary to follow a diet and drinking regime. You should drink up to 1.2 liters of liquid per day. And you should exclude everything fried, fatty, salty, spicy, and smoked from your diet. It will be better if the patient switches to steamed and boiled dishes during treatment.

If your attending physician allows, you can adjust the glomerular filtration rate folk remedies. Thus, ordinary parsley, whose diuresis-improving properties have been known for a long time, increases GFR well. Its dry seeds and roots (in a volume of 1 tbsp) are steamed with boiling water (500 ml) and kept for 2-3 hours. Then strain the infusion and drink 0.5 cups twice a day.

You can also use rosehip root to increase GFR. It is in the amount of 2 tbsp. pour boiling water and cook over low heat for 15 minutes. Then strain the broth and drink 70 ml three times during the day. This drug also increases diuresis, which will certainly increase GFR.

It is important to know that the entire treatment process should be supervised only by a specialist. Self-medication is strictly prohibited.

A healthy kidney consists of 1-1.2 million units renal tissue- nephrons, functionally connected to blood vessels. Each nephron is about 3 cm long, in turn, consists of a vascular glomerulus and a system of tubules, the length of which in a nephron is 50 - 55 mm, and all nephrons are about 100 km. In the process of urine formation, nephrons remove metabolic products from the blood and regulate its composition. 100–120 liters of so-called primary urine are filtered per day. Most of the liquid is absorbed back into the blood - with the exception of “harmful” and Not needed by the body substances. Only 1–2 liters of secondary concentrated urine enters the bladder.

Because of various diseases nephrons fail one after another, mostly irreversibly. The functions of the dead “brothers” are taken over by other nephrons; at first there are so many of them. However, over time, the load on efficient nephrons becomes more and more - and, having become overworked, they die faster and faster.

How to evaluate kidney function? If it were possible to accurately count the number of healthy nephrons, it would probably be one of the most accurate indicators. However, there are other methods. You can, for example, collect all the patient’s urine for a day and simultaneously analyze his blood - calculate creatinine clearance, that is, the rate of purification of this substance from the blood.

Creatinine is the end product of protein metabolism. The normal level of creatinine in the blood is 50-100 µmol/l in women and 60-115 µmol/l in men; in children these figures are 2-3 times lower. There are other normal indicators (not higher than 88 µmol/l); such discrepancies partly depend on the reagents used in the laboratory and on the development of the patient’s muscle mass. With well-developed muscles, creatinine can reach 133 µmol/l, with small muscle mass- 44 µmol/l. Creatinine is formed in muscles, so its slight increase is possible in severe muscle work and extensive muscle injuries. All creatinine is excreted by the kidneys, approximately 1-2 g per day.

However, even more often, to assess the degree of chronic renal failure, an indicator such as GFR is used - glomerular filtration rate (ml/min).

NORMAL GFR ranges from 80 to 120 ml/min, lower in older people. GFR below 60 ml/min is considered the onset of chronic renal failure.

Here are several formulas that allow you to evaluate kidney function. They are quite well known among specialists, I quote them from a book written by specialists from the dialysis department of the St. Petersburg city Mariinsky hospital (Zemchenkov A.Yu., Gerasimchuk R.P., Kostyleva T.G., Vinogradova L.Yu., Zemchenkova I .G. “Life with chronic kidney disease”, 2011).

This, for example, is the formula for calculating creatinine clearance (Cockcroft-Gault formula, after the names of the authors of the formula: Cockcroft and Gault):

Ccr = (140 – age, years) x weight kg/ (creatinine in mmol/l) x 814,

For women, the resulting value is multiplied by 0.85

Meanwhile, in fairness, it must be said that European doctors do not recommend using this formula to assess GFR. For more precise definition For residual kidney function, nephrologists use the so-called MDRD formula:

GFR = 11.33 x Crk –1.154 x (age) – 0.203 x 0.742 (for women),

where Crк is blood serum creatinine (in mmol/l). If the test results give creatinine in micromoles (μmol/L), this value should be divided by 1000.

The MDRD formula has a significant drawback: it does not work well at high GFR values. Therefore, in 2009, nephrologists developed a new formula for estimating GFR, CKD-EPI formula. The results of estimating GFR using the new formula are consistent with the results of MDRD at low values, but provide a more accurate estimate at high values of GFR. Sometimes it happens that a person has lost significant amount kidney function and his creatinine is still normal. This formula is too complex to present here, but it is worth knowing that it exists.

And now about the stages chronic illness kidney:

1 (GFR greater than 90). Normal or increased GFR in the presence of a disease affecting the kidneys. Observation by a nephrologist is required: diagnosis and treatment of the underlying disease, reducing the risk of developing cardiovascular complications

2 GFR=89-60). Kidney damage with moderate reduction in GFR. Assessment of the rate of progression of CKD, diagnosis and treatment is required.

3 (GFR=59-30). Average degree decrease in GFR. Prevention, detection and treatment of complications are necessary

4 (GFR=29-15). Pronounced degree of reduction in GFR. It's time to prepare for replacement therapy(method selection required).

5 (GFR less than 15). Kidney failure. Initiation of renal replacement therapy.

Estimation of glomerular filtration rate according to the level of creatinine in the blood (abbreviated MDRD formula):

Read more about kidney function on our website:

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Glomerular filtration of the kidneys is a process as a result of which water and some substances dissolved in it are passively released from the blood into the lumen of the nephron capsule through the renal membrane. This process, along with others (secretion, reabsorption), is part of the mechanism of urine formation.

Measuring glomerular filtration rate has a large clinical significance. Although indirectly, it quite accurately reflects the structural and functional characteristics kidneys, namely, the number of functioning nephrons and the condition of the renal membrane.

Nephron structure

Urine is a concentrate of substances, the removal of which from the body is necessary to maintain constancy internal environment. This is a kind of “waste” from life, including toxic ones, the further transformation of which is impossible, and the accumulation is harmful. The function of removing these substances is performed by the urinary system, the main part of which is the kidneys - biological filters. Blood passes through them, freeing itself from excess fluid and toxins.

Nephron is component kidneys, thanks to which it performs its function. Normally, the kidney has about 1 million nephrons, and each produces a certain amount of urine. All nephrons are connected by tubules through which urine is collected in the pyelocaliceal system and removed from the body through the urinary tract.

In Fig. Figure 1 schematically shows the structure of the nephron. A – renal corpuscle: 1 – afferent artery; 2– efferent artery; 3 – epithelial layers of the capsule (external and internal); 4 – beginning of the nephron tubule; 5 – vascular glomerulus. B – nephron itself: 1 – glomerular capsule; 2 – nephron tubule; 3 – collecting duct. Blood vessels nephron: a – afferent artery; b – efferent artery; c – tubular capillaries; d – nephron vein.

Rice. 1

At different pathological processes Reversible or irreversible damage to the nephrons occurs, as a result of which some of them may cease to perform their functions. The result is a change in urine production (retention of toxins and water, loss of nutrients through the kidneys and other syndromes).

The concept of glomerular filtration

Consists of several stages. At each stage, a failure may occur, leading to dysfunction of the entire organ. The first stage of urine formation is called glomerular filtration.

It is carried out by the renal corpuscle. It consists of a network of small arteries formed in the form of a glomerulus surrounded by a two-layer capsule. The inner layer of the capsule fits tightly to the walls of the arteries, forming a renal membrane (glomerular filter, from the Latin glomerulus - glomerulus).

It consists of the following elements:

endothelial cells (the inner “lining” of arteries);
epithelial capsule cells forming its inner layer;
layer of connective tissue(basal membrane).

It is through the renal membrane that water is released and various substances, and how fully the kidneys perform their function depends on its condition.

Through the renal membrane, water is passively filtered from the blood along a pressure gradient, and along with it, substances with small molecular sizes are released along an osmotic gradient. This process is glomerular filtration.

Large (protein) molecules and cellular elements of the blood do not pass through the kidney membrane. In some diseases, they can still pass through it due to its increased permeability and end up in the urine.

The solution of ions and small molecules in the filtered liquid is called primary urine. The content of substances in its composition is very low. It is similar to plasma from which the protein has been removed. The kidneys filter from 150 to 190 liters of primary urine in one day. During the further transformation that primary urine undergoes in the nephron tubules, its final volume decreases by approximately 100 times, to 1.5 liters (secondary urine).

Tubular secretion and reabsorption - the processes of formation of secondary urine

Due to the fact that during passive tubular filtration it enters the primary urine a large number of water and substances needed by the body, removing it from the body unchanged would be biologically impractical. In addition, some toxic substances are formed in quite large quantities, and their elimination should be more intense. Therefore, primary urine, passing through the tubular system, undergoes transformation through secretion and reabsorption.

In Fig. Figure 2 shows diagrams of tubular reabsorption and secretion.

Rice. 2

Tubular reabsorption (1). This is the process by which water, as well as necessary substances through the work of enzyme systems, mechanisms of ion exchange and endocytosis, it is “taken” from primary urine and returned to the bloodstream. This is possible due to the fact that the nephron tubules are densely entwined with capillaries.

Tubular secretion (2) is the reverse process of reabsorption. This is the elimination of various substances using special mechanisms. Epithelial cells actively, contrary to the osmotic gradient, they “remove” some substances from the vascular bed and secrete them into the lumen of the tubules.

As a result of these processes, there is an increase in the concentration of harmful substances in the urine, the elimination of which is necessary, compared to their concentration in the plasma (for example, ammonia, metabolites medicinal substances). It also prevents the loss of water and nutrients (for example, glucose).

This ratio of filtration mechanisms, as well as secretion and reabsorption, determines the volume of excretion (release) of certain substances along with urine.

Some substances are indifferent to the processes of secretion and reabsorption; their content in the urine is proportional to that in the blood (one example is insulin). Correlating the concentration of such a substance in urine and blood allows us to draw a conclusion about how well or poorly glomerular filtration occurs.

Glomerular filtration rate: clinical significance, principle of determination

Glomerular filtration rate (GFR) is an indicator that is the main quantitative reflection of the process of formation of primary urine. In order to understand what changes reflect fluctuations in this indicator, it is important to know what GFR depends on.

It is influenced by the following factors:

The volume of blood passing through the vessels of the kidneys in a certain time period.
Filtration pressure is the difference between the pressure in the arteries of the kidney and the pressure of filtered primary urine in the capsule and tubules of the nephron.
Filtration surface is the total area of capillaries that participate in filtration.
Number of functioning nephrons.

You can calculate the glomerular filtration rate using the formulas

The first 3 factors are relatively variable and are regulated through local and general neurohumoral mechanisms. The last factor - the number of functioning nephrons - is quite constant, and it is this factor that most strongly influences the change (decrease) in glomerular filtration rate. Therefore in clinical practice GFR is most often studied to determine the stage of chronic renal failure (it develops precisely due to the loss of nephrons due to various pathological processes).

GFR is most often determined by a calculation method based on the ratio of the content in the blood and urine of a substance that is always present in the body - creatinine.

This test is also called endogenous creatinine clearance (). There are special formulas for calculating GFR; they can be used in calculators and computer programs. The calculation is not particularly difficult. IN normal GFR is:

75–115 ml/min in women;
95–145 ml/min in men.

Determination of glomerular filtration rate is the method most commonly used to assess kidney function and the stage of renal failure. Based on the results of this analysis (including), a prognosis of the course of the disease is made, treatment regimens are developed, and the issue of transferring the patient to dialysis is decided.