What is the composition of primary urine similar to? Urine formation diagram. Influence of the concentration of substances circulating in the blood on the degree of filtration in the kidneys

Their functions include removing unnecessary metabolic products and foreign substances from the body, regulation of the chemical composition of body fluids by removing substances, the amount of which exceeds current needs, regulation of water content in body fluids(and thus their volume) and regulation of the pH of body fluids .

The kidneys are abundantly supplied with blood and homeostatically regulate blood composition... Thanks to this, the optimal composition is maintained tissue fluid, and, consequently, the intracellular fluid of the cells washed by it, which ensures their efficient work.

The kidneys adapt their activity to changes in the body. Moreover, only in the last two departments nephron- v distal convoluted tubule of the kidney and collecting tube of the kidney- functional activity changes in order to regulation of the composition of body fluids... The rest of the nephron up to the distal tubule functions in the same way in all physiological conditions.

The end product of kidney activity is urine, the volume and composition of which varies depending on the physiological state of the organism.

Each kidney contains about one million structural and functional units (nephrons). A schematic of the nephron is shown in Fig. No. 1

Figure № 1. The structure of the renal glomerulus and nephron with blood vessels:

1-bringing artery; 2-outflow artery; 3-glomerular capillary network; 4-capsule Bowman; 5-proximal tubule; 6-distal tubule; 7. collecting ducts; 8-capillary network of the cortex and medulla of the kidneys.

The blood plasma that has entered the kidneys (about 20% of the total cardiac output) is ultrafiltered in the glomeruli. Each glomerulus contains renal capillaries surrounded by Bowman's capsule. The driving force providing ultrafiltration is a gradient between blood pressure and hydrostatic pressure of the glomerular space, which is about 8 kPa. Ultrafiltration is counteracted by an oncotic pressure of about 3.3 kPa, created by dissolved plasma proteins, which themselves practically do not undergo ultrafiltration (Fig. No. 2).

Figure № 2. Forces providing filtration of plasma in the glomeruli of the kidneys

	Figure № 3. Urinary organs
	kidney cortex medulla
	renal cups
	pelvis
	ureter
	bladder
	Urethra

The process of urine formation takes place in two stages. The first one takes place in the capsules of the outer layer of the kidneys (renal glomerulus). All the liquid part of the blood that enters the glomeruli of the kidneys is filtered and enters the capsules. This is how primary urine is formed, which is practically blood plasma.

Along with the products of dissimilation, the primary urine contains both amino acids and glucose, and many other compounds necessary for the body. Only proteins from blood plasma are absent in primary urine. This is understandable: after all, proteins are not filtered.

The second stage of urine formation is that the primary urine passes through a complex system of tubules, where the substances and water necessary for the body are sequentially absorbed. Everything harmful to the life of the body remains in the tubules and in the form of urine is excreted from the kidneys through the ureters into the bladder. This final urine is called secondary urine.

How does this process take place?

Primary urine passes continuously through the convoluted renal tubules. The epithelial cells that make up their walls do a tremendous job. They actively suck up a large amount of water and all the substances necessary for the body from the primary urine. From the epithelial cells, they return to the blood flowing through the capillary network that braids the renal tubules.

How great is the work done by the renal epithelium can be judged, for example, by the fact that its cells absorb about 96% of the water contained in the primary urine. The cells of the renal epithelium spend a huge amount of energy on their work. Therefore, the metabolism occurs in them very intensively. This is confirmed by the fact that the kidneys, which make up only 1/160 of our body weight, consume approximately 1/11 of the oxygen entering it. The resulting urine flows through the tubes of the pyramids to the papillae and seeps through the holes in them into the renal pelvis. From there, it flows down the ureters into the bladder and is removed outside (Fig. No. 3).

The presence of the genitourinary system in a person makes it possible to quickly remove waste products from the body, formed during previously passing processes. The formation of urine is a vital process carried out by the kidneys and is carried out in three main stages: filtration, reabsorption and secretion. Violation in the formation and excretion of urine can lead to certain types of rather serious diseases. In this case, the investigated primary and secondary urine, or rather the result of the analysis, will immediately show any violations that have arisen, which will be a significant reason for further examination and treatment.

Primary urine is called the fluid that is formed in the kidneys after the filtration of substances present in the blood, which have a low molecular weight, from formed elements and proteins. By the name of the elements included in the primary urine, it can be compared with blood plasma, in which amino acids, creatinine, glucose, urea, low molecular weight complexes and free ions are also present in the exact amount. After the formation of primary urine and its passage through the tubules through the cells of their walls, a large amount of water goes back into the blood, as well as those substances that are necessary for the body to function normally. This entire process of passing and returning the contents of the primary urine is called reabsorption.

In the process of reabsorption, some substances are completely absorbed by the body. Such substances are glucose and various amino acids. Mineral salts and water are "taken away" by human blood. All that remains after this whole process is called secondary urine. That is, it is it that is handed over for analysis in the laboratory and its composition and other parameters are examined.

Secondary urine composition

The main components of secondary urine include:

• water,
• urea,
• ammonia,
• various sulfates,
• chlorine,
• sodium.

The total volume of secondary urine, which includes all of the above components, exceeds one liter per day. It can be large if a person consumes much more water than his body needs, and less if the ambient temperature is high enough. The usual color of urine is yellow, due to the presence of bile pigments in the composition, some of which, being absorbed in the intestine, go into the bloodstream, are filtered by the kidneys, but are not reabsorbed. The frequency of urine excretion from the body is determined by the volume.

The need to analyze the composition of secondary urine

The composition of the secondary urine is examined to determine the presence of certain diseases in the human body. In this case, you can quickly diagnose a violation in the work of organs such as the bladder, kidneys and prostate. In addition, urine is analyzed when there is suspicion of urolithiasis and nephrosclerosis.

Collecting material for research

In order to achieve reliable results, the correct collection of urine is very important. In order to pass the analysis correctly, you must first perform hygienic procedures for the genitals. Secondary urine should be collected in a sterile dry container and closed tightly with a lid. All this is explained by the fact that the concentration of substances in the material for research can change under the influence of external factors on it, as well as the presence of water and detergents in the container. In order to avoid this, there are currently special containers, the use of which will help to minimize the likelihood of obtaining unreliable results.

Features of collecting material for research in children

Children, especially those under the age of one and a half years, cannot control the urge to urinate, which causes certain problems with the collection of material. But in most cases, this analysis is mandatory and is given quite often. That is why secondary urine from children is collected in a special way using special urine bags. These elements are attached to the previously thoroughly washed genitals and detached from them after the urine is inside it. The resulting liquid is poured into a sterile container.

Thus, the formation of secondary urine is a rather important process that allows not only to remove excess water and unnecessary substances and elements from the body, but also to diagnose this or that disease during the time. This analysis is one of the simplest for both the patient and the laboratory assistants, so there are no restrictions on its delivery. But in order to get a reliable result, it is necessary to fulfill a number of requirements when passing this analysis. Compliance with all the rules will be able to make it clear about the presence of violations and make a decision about the need for treatment.

The formation of the final urine, its composition and properties. The importance of various parts of the nephron in the formation of the final urine.

The kidneys consume 9% of the total oxygen used by the body. The high intensity of metabolism in the kidneys is due to the high energy intensity of the processes of urine formation.

The process of formation and excretion of urine is called diuresis; it proceeds in three phases: filtration, reabsorption and secretion.

Blood enters the vascular glomerulus of the renal corpuscle from the bringing arteriole. The hydrostatic pressure of blood in the vascular glomerulus is quite high - up to 70 mm Hg. Art. In the lumen of the Shumlyansky-Bowman capsule, it reaches only 30 mm Hg. Art. The inner wall of the Shumlyansky-Bowman capsule grows tightly with the capillaries of the vascular glomerulus, thereby forming a kind of membrane between the lumen of the capillary and the capsule. At the same time, small spaces remain between the cells that form it. A semblance of the smallest lattice (sieve) appears. In this case, arterial blood flows through the capillaries of the glomerulus rather slowly, which maximally facilitates the transition of its components into the lumen of the capsule.

The combination of increased hydrostatic pressure in the capillaries and reduced pressure in the lumen of the Shumlyansky-Bowman capsule, the slow blood flow and the peculiarity of the structure of the walls of the capsule and glomerulus create favorable conditions for filtering blood plasma - the transition of the liquid part of the blood into the lumen of the capsule due to the pressure difference. The resulting filtrate is collected in the lumen of the Shumlyansky-Bowman capsule and is called primary urine. It should be noted that the decrease in blood pressure below 50 mm Hg. Art. (for example, with blood loss) leads to the cessation of the formation of primary urine.

Primary urine differs from blood plasma only by the absence of protein molecules in it, which, due to their size, cannot pass through the wall of the capillaries into the capsule. It also contains metabolic products (urea, uric acid, etc.) and other constituents of plasma, including substances necessary for the body (amino acids, glucose, vitamins, salts, etc.).

The main quantitative characteristic of the filtration process is the glomerular filtration rate (GFR) - the amount of primary urine generated per unit of time. Normally, the glomerular filtration rate is 90-140 ml per minute. During the day, 130-200 liters of primary urine are formed (this is about 4 times more than the total amount of fluid in the body). In clinical practice, the Reberg test is used to calculate GFR. Its essence lies in the calculation of creatinine clearance. Clearance - the volume of blood plasma, which, passing through the kidneys for a certain time (1 min), is completely cleared of this or that substance. Creatinine is an endogenous substance, the concentration of which in the blood plasma is not subject to sharp fluctuations. This substance is excreted only by the kidneys by filtration. It practically does not undergo secretion and reabsorption.

Primary urine from the capsule enters the tubules of the nephron, where reabsorption takes place. Tubular reabsorption is the process of transporting substances from primary urine into the blood. It occurs due to the work of the cells lining the walls of the convoluted and straight tubules of the nephron. The latter actively suck back glucose, amino acids, vitamins, Na +, K +, C1-, HCO3- ions from the nephron lumen into the secondary capillary network of the kidney. For most of these substances, there are special carrier proteins on the membrane of the epithelial cells of the tubules. These proteins, using the energy of ATP, transfer the corresponding molecules from the lumen of the tubules into the cytoplasm of the cells. From here they enter the capillaries, entwining the tubules. Water absorption occurs passively, along the osmotic pressure gradient. It depends primarily on the reabsorption of sodium and chlorine ions. A small amount of protein that gets into the primary urine during filtration is reabsorbed by pinocytosis.

Thus, reabsorption can occur passively, according to the principle of diffusion and osmosis, and actively - due to the activity of the epithelium of the renal tubules with the participation of enzyme systems with the expenditure of energy. Normally, about 99% of the primary urine volume is reabsorbed.

Many substances with an increase in their concentration in the blood cease to fully undergo reabsorption. These include, for example, glucose. If its concentration in the blood exceeds 10 mmol / L (for example, in diabetes mellitus), glucose begins to appear in the urine. This is due to the fact that carrier proteins cannot cope with the increased amount of glucose coming from the blood into the primary urine.

In addition to reabsorption in the tubules, a secretion process takes place. It involves the active transport of certain substances by epithelial cells from the blood into the lumen of the tubule. As a rule, the secretion goes against the concentration gradient of the substance and requires the expenditure of ATP energy. Thus, many xenobiotics (dyes, antibiotics and other drugs), organic acids and bases, ammonia, ions (K +, H +) can be removed from the body. It should be emphasized that each substance has its own strictly defined mechanisms of excretion by the kidneys. Some of them are excreted only by filtration, and practically do not undergo secretion (creatinine); others, on the contrary, are removed mainly by secretion; for some, both mechanisms of excretion from the body are characteristic.

As a result of the processes of reabsorption and secretion from the primary urine, secondary, or final urine is formed, which is excreted from the body. The formation of final urine occurs as the filtrate passes through the tubules of the nephron. Thus, from 130-200 liters of primary urine within 1 day, only about 1.0-1.5 liters of secondary urine is formed and excreted from the body.

Composition and properties of secondary urine. Secondary urine is a clear, light yellow liquid containing 95% water and 5% dry residue. The latter is represented by products of nitrogen metabolism (urea, uric acid, creatinine), potassium and sodium salts, etc.

The urine response is inconsistent. During muscular work, acids accumulate in the blood. They are excreted by the kidneys and, therefore, the urine reaction becomes acidic. The same is observed when eating protein foods. When eating plant foods, the urine reaction is neutral or even alkaline. At the same time, most often urine is a weakly acidic environment (pH 5.0-7.0). Normally, there are pigments in the urine, such as urobilin. They give it a characteristic yellowish color. Urine pigments are formed in the intestines and kidneys from bilirubin. The appearance of unchanged bilirubin in the urine is characteristic of diseases of the liver and biliary tract.

The relative density of urine is proportional to the concentration of substances dissolved in it (organic compounds and electrolytes) and reflects the concentration ability of the kidneys. On average, its specific gravity is 1.012-1.025 g / cm3. It decreases with the consumption of large amounts of liquid. The relative density of urine is determined using a urometer.

Normally, there is no protein in urine. Its appearance there is called proteinuria. This condition is indicative of kidney disease. It should be noted that protein can be found in urine and in healthy people after intense exercise.

Glucose in a healthy person is usually not found in urine. Its appearance is associated with an excessive concentration of a substance in the blood (for example, in diabetes mellitus). The appearance of glucose in the urine is called glucosuria. Physiological glucosuria is observed during stress, eating increased amounts of carbohydrates.

After centrifugation of the urine, a supernatant is obtained, which is used for examination under a microscope. In this case, a number of cellular and non-cellular elements can be identified. The first include epithelial cells, leukocytes and erythrocytes. Normally, the content of epithelial cells of the tubules of the kidneys and urinary tract should not exceed 0-3 in the field of view. This is the normal content of leukocytes. With an increase in the content of leukocytes above 5 - 6 in the field of view, they speak of leukocyturia; above 60 - pyuria. Leukocyturia and pyuria are signs of inflammatory diseases of the kidneys or urinary tract. Normally, red blood cells in urine are found in a single amount. If their content increases, they speak of hematuria. Non-cellular elements include cylinders and unorganized sediment. Cylinders are protein formations that are not found in the urine of a healthy person. They are formed in the tubules of the nephron and have a cylindrical shape, repeating the shape of the tubules. Fugitive sediments are salts and crystalline formations found in normal and abnormal urine. Bacteria can also be found in urine (the normal value is no more than 50,000 in 1 ml; with large numbers, they speak of bacteriuria).

As a result of glomerular filtration, primary urine . In its composition, it is similar to blood plasma, but does not contain high molecular weight proteins and lipids. In 4-5 minutes, all the blood passes through the kidneys. They receive more blood than any organ of the body, even 4-5 times more than the heart and brain. However, a greater amount of it is used not to feed the kidney, but to cleanse the blood from toxic products. In a minute, as a result of glomerular filtration, 70-120 ml of filtrate is formed, and in a day - 100-150 liters. The external arteriole, leaving the capsule, branches again and forms a network of capillaries that braid the convoluted canals of the nephron almost along their entire length.

During the passage of primary urine through the tubules through the epithelial cells of their walls, a significant amount of water and substances necessary for the body are returned to the blood. This process is called reabsorption (reverse absorption). It is carried out at the expense of significant energy expenditure of the body. Some substances (glucose, amino acids) are completely reabsorbed, and mineral salts and water are absorbed from the tubules into the blood in the amounts required by the body. After reabsorption, urine is called secondary, or final.Material from the site

Secondary urine - this is mainly excess water, sodium chloride and urea. Its yellow color is predetermined by bile pigments, part of which is absorbed in the small intestine, enters the bloodstream, is filtered by the kidneys, but is not reabsorbed. For a day, 1.5-2.5 liters of secondary urine are formed in the human body. The amount of urine per day changes with a change in the drinking regime, ambient temperature, excessive salt intake.

The secondary urine should not contain glucose, proteins and blood cells.

On this page material on topics:

• Explain where and how primary urine is generated in a nutshell

• How primary and secondary urine are formed a short description

• Flat round annelids primary and secondary urine

• Explain the mechanisms of formation of primary and secondary urine

• Secondary urine forms minutes after water absorption

Questions about this material:

History

Primary urine was first described by Karl Ludwig (1816-1895) in 1842 in his doctoral dissertation "Contribution to the theory of the mechanism of urine excretion" (German: "Beiträge zur Lehre vom Mechanismus der Harnabsonderung").

Composition

Primary urine by its composition is plasma, practically devoid of proteins. Namely, the amount of creatinine, amino acids, glucose, urea, low molecular weight complexes and free ions in the ultrafiltrate coincides with their amount in the blood plasma. Due to the fact that the glomerular filter does not pass proteins-anions, in order to maintain Donnan's membrane equilibrium (the product of ion concentrations on one side of the membrane is equal to the product of their concentrations on the other side) in the primary urine, the concentration of chlorine and bicarbonate anions becomes about 5% higher and, accordingly, the concentration of sodium and potassium cations is proportionally lower than in blood plasma. The ultrafiltrate contains a small amount of one of the smallest protein molecules - almost 3% of hemoglobin and about 0.01% of albumin.

Properties

Primary urine has the following properties:

1. Low osmotic pressure. It arises from membrane equilibrium.
2. Large daily volume, which is measured in tens of liters. The entire volume of blood passes through the kidneys about 300 times. Because on average, a person has 5 liters of blood, then the kidneys filter about 1500 liters of blood per day and form about 150-180 liters of primary urine.

Glomerular filtration rate (GFR)

GFR is regulated by nervous and humoral mechanisms and affects:

• the tone of the glomerular arterioles and, consequently, the volume of blood flow (plasma flow) and the magnitude of the filtration pressure;
• the tone of the mesangial cells (connective tissue between the capillaries of the nephron glomerulus) and the filtration surface;
• activity of visceral epithelial cells (or podocytes) and their functions.

Humoral factors such as prostaglandins, atriopeptides, norepinephrine and epinephrine, adenosine, and the like. can both increase and decrease glomerular filtration. The most important role in the constancy of GFR is played by the autoregulation of cortical blood flow.

Meaning

Primary urine undergoes further concentration and removal of useful substances from it. The resulting concentrated residue is secondary urine.

Links

1. Primary urine (glomerular ultrafiltrate). Regulation of the glomerular filtration rate (GFR).
2. E.V. Trifonov Human pneumopsychosomatology. Rus.-eng.-rus. encyclopedia, 15th ed., 2012 = Tryphonov E.B. Human Pneumapsychosomatology. The Rus.-Engl.-Rus. Encyclopedia, 15th ed., 2012.

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See what "Primary urine" is in other dictionaries:

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