Kidneys. The structure of the kidneys. Nephron. Functions and structure of the nephron. The structure and function of the nephron: renal tubules

Nephron capsule (Bowman-Shunliansky capsule)

proximal convoluted tubule

Proximal straight tubule

Loop of Henle

Descending division (thin)

Kaleno loops

Ascending division (distal rectal tubule)

distal convoluted tubule

In the center:

medulla

There are three types of nephrons

True cortical nephrons (1%) - all departments lie in the cortical substance

Intermediate nephrons (79%) - the fenugreek loop sinks into the medulla, and the rest lie in the cortex

Juxta-medullary (paracerebral) (20%) - in them the loop lies completely in the medulla, the remaining sections are located on the border between the cortical and medulla.

Function of the first two nephrons: participation in urination.

Function of the third nephron: performs the role of a shunt during heavy physical exertion, dumps a larger volume of blood and performs an endocrine function.

Blood supply of nephrons

It is divided into:

1. Kartikalnaya (cortical) - blood supply to 1.2 nephrons

2. Juxto-medullary - blood supply to 3 nephrons

Blood supply to the cardial nephrons:

The renal artery enters the gates of the kidney, then the interlobar, then the arcuate (located on the border between the cortical and medulla), then the interlobular, then the afferent arteriole, which approaches the nephron capsule, then the vascular glomerulus formed by a network of capillaries (the miraculous network), then the efferent arteriole, then the secondary network of capillaries, then the outflow of blood. From the subcapsular part, blood is collected in the stellate vein, from which the interlobular vein departs. From the rest of the cortex, the venules open into the interlobular vein, from which the arcuate vein, interlobar vein, and renal vein. The afferent and efferent arterioles are of different diameters, the efferent arteriole is smaller than the efferent arteriole. The pressure difference in the arterioles causes high pressure in the vascular glomerulus (70-90 mm Hg). the secondary part of the capillaries braids the renal tubules and has low blood pressure (10-12 mm Hg).

Features of the blood supply of the juxta-medullary nephrons:

1. Afferent and efferent arterioles of the same diameter, therefore, there is not high pressure in the vascular glomerulus, the filtration process is not possible.

2. The efferent arteriole forms a secondary network of capillaries and a direct artery, which goes to the medulla and there branches into a capillary network (formed as a result of 3 capillary networks).

3. The outflow of blood is carried out through a direct vein coming from the medulla, then the arcuate, then the interlobar and renal vein.

The structure of the departments of the nephron and the process of urination:

There are three phases in the process of urination:

Filtration (formation of primary urine) - the filtration process occurs in the renal corpuscle, which consists of a nephron capsule and a vascular glomerulus. The vascular glomerulus is formed by capillaries in the amount of 50-100, located in the form of loops. The nephron capsule looks like a double-walled bowl, it contains:

The outer leaflet is formed by a single-layered squamous epithelium, turning into a cubic one.

Inner leaf - formed by podocyte cells. Podocyte cells have a flattened shape, their nuclear-free part forms outgrowths - cytotrabeculae, from which cytopogia extend. Cells are located on a three-layer basement membrane. In the basement membrane, the outer and inner layers are light, they have few collagen fibers, but a lot of amorphous substance. The middle layer of the membrane is dark, consists of bundles of collagen fibers, which are not ordered and form a network. The cell diameter is constant and equal to 7 nm (this basement membrane has selective permeability). Finestrated endothelium is attached to the same basement membrane from the side of the capillary. Podocyte cells, a three-layer basement membrane, and finely endothelium form a filtration barrier through which primary urine enters the capsule cavity. This is blood plasma devoid of high molecular weight proteins.

The filtration process is due to the pressure difference between high pressure in the glomerulus and low pressure in the capsule cavity (due to the pressure difference between the afferent and efferent arterioles).

slit-like cavity between them

Reabsorption

Acidification

Primary urine enters the proximal tubule, this is a tube with a diameter of 50 microns, in the wall there is: a single-layer cubic or low prismatic epithelium, the cells have microvilli forming a border in the apical part, and basal striation (folds of plasmalemma and mitochondria) in the basal part. It has rounded nuclei and pinocytic vesicles. Glucose, amino acids, which are formed after the breakdown of low molecular weight proteins, and some electrolytes enter the blood through the wall of the proximal tubule. The microvilli will have alkaline phosphotase. This is a mandatory process, will depend on the concentration of substances in the blood. The process is called obligate reabsorption. Next comes the process facultative re-absorption.

Normal blood filtration is guaranteed by the correct structure of the nephron. It carries out the processes of reuptake of chemicals from plasma and the production of a number of biologically active compounds. The kidney contains from 800 thousand to 1.3 million nephrons. Aging, an unhealthy lifestyle and an increase in the number of diseases lead to the fact that with age the number of glomeruli gradually decreases. To understand the principles of the nephron, it is worth understanding its structure.

Description of the nephron

The main structural and functional unit of the kidney is the nephron. The anatomy and physiology of the structure is responsible for the formation of urine, the reverse transport of substances and the production of a spectrum of biological substances. The structure of the nephron is an epithelial tube. Further, networks of capillaries of various diameters are formed, which flow into the collecting vessel. The cavities between the structures are filled with connective tissue in the form of interstitial cells and matrix.

The development of the nephron is laid down in the embryonic period. Different types of nephrons are responsible for different functions. The total length of the tubules of both kidneys is up to 100 km. Under normal conditions, not all of the glomeruli are involved, only 35% work. The nephron consists of a body, as well as a system of channels. It has the following structure:

• capillary glomerulus;
• capsule of the renal glomerulus;
• near tubule;
• descending and ascending fragments;
• distant straight and convoluted tubules;
• connecting path;
• collecting ducts.

Functions of the nephron in humans

Up to 170 liters of primary urine are formed per day in 2 million glomeruli.

The concept of nephron was introduced by the Italian physician and biologist Marcello Malpighi. Since the nephron is considered an integral structural unit of the kidney, it is responsible for the following functions in the body:

• blood purification;
• formation of primary urine;
• return capillary transport of water, glucose, amino acids, bioactive substances, ions;
• the formation of secondary urine;
• ensuring salt, water and acid-base balance;
• regulation of blood pressure;
• secretion of hormones.

The nephron begins as a capillary glomerulus. This is the body. The morphofunctional unit is a network of capillary loops, up to 20 in total, which are surrounded by a nephron capsule. The body receives its blood supply from the afferent arteriole. The vessel wall is a layer of endothelial cells, between which there are microscopic gaps up to 100 nm in diameter.

In capsules, internal and external epithelial balls are isolated. Between the two layers there is a slit-like gap - the urinary space, where the primary urine is contained. It envelops each vessel and forms a solid ball, thus separating the blood located in the capillaries from the spaces of the capsule. The basement membrane serves as a support base.

The nephron is arranged according to the type of filter, the pressure in which is not constant, it changes depending on the difference in the width of the gaps of the afferent and efferent vessels. The filtration of blood in the kidneys takes place in the glomerulus. Blood cells, proteins, usually cannot pass through the pores of the capillaries, since their diameter is much larger and they are retained by the basement membrane.

Capsule podocytes

The nephron consists of podocytes, which form the inner layer in the nephron capsule. These are large stellate epithelial cells that surround the renal glomerulus. They have an oval nucleus, which includes scattered chromatin and plasmosome, transparent cytoplasm, elongated mitochondria, a developed Golgi apparatus, shortened cisterns, few lysosomes, microfilaments, and several ribosomes.

Three types of podocyte branches form pedicles (cytotrabeculae). The outgrowths closely grow into each other and lie on the outer layer of the basement membrane. Structures of cytotrabeculae in nephrons form a cribriform diaphragm. This part of the filter has a negative charge. They also require proteins to function properly. In the complex, blood is filtered into the lumen of the nephron capsule.

basement membrane

The structure of the basement membrane of the kidney nephron has 3 balls about 400 nm thick, consists of a collagen-like protein, glyco- and lipoproteins. Between them are layers of dense connective tissue - mesangium and a ball of mesangiocytitis. There are also gaps up to 2 nm in size - the pores of the membrane, they are important in the processes of plasma purification. On both sides, the sections of connective tissue structures are covered with glycocalyx systems of podocytes and endotheliocytes. Plasma filtration involves some of the matter. The basement membrane of the glomeruli of the kidneys functions as a barrier through which large molecules must not penetrate. Also, the negative charge of the membrane prevents the passage of albumins.

Mesangial matrix

In addition, the nephron consists of mesangium. It is represented by systems of connective tissue elements that are located between the capillaries of the Malpighian glomerulus. It is also a section between the vessels, where there are no podocytes. Its main composition includes loose connective tissue containing mesangiocytes and juxtavascular elements, which are located between two arterioles. The main work of the mesangium is supportive, contractile, as well as ensuring the regeneration of the components of the basement membrane and podocytes, as well as the absorption of old constituent components.

proximal tubule

The proximal capillary renal tubules of the nephrons of the kidney are divided into curved and straight. The lumen is small in size, it is formed by a cylindrical or cubic type of epithelium. At the top is placed a brush border, which is represented by long villi. They form an absorbent layer. The extensive surface area of ​​the proximal tubules, the large number of mitochondria, and the close location of the peritubular vessels are designed for selective uptake of substances.

The filtered fluid flows from the capsule to other departments. The membranes of closely spaced cellular elements are separated by gaps through which fluid circulates. In the capillaries of the convoluted glomeruli, 80% of the plasma components are reabsorbed, among them: glucose, vitamins and hormones, amino acids, and in addition, urea. The functions of the nephron tubules include the production of calcitriol and erythropoietin. The segment produces creatinine. Foreign substances that enter the filtrate from the interstitial fluid are excreted in the urine.

The structural and functional unit of the kidney consists of thin sections, also called the loop of Henle. It consists of 2 segments: descending thin and ascending thick. The wall of the descending section with a diameter of 15 μm is formed by a squamous epithelium with multiple pinocytic vesicles, and the ascending section is formed by a cubic one. The functional significance of the nephron tubules of the loop of Henle covers the retrograde movement of water in the descending part of the knee and its passive return in the thin ascending segment, the reuptake of Na, Cl and K ions in the thick segment of the ascending fold. In the capillaries of the glomeruli of this segment, the molarity of urine increases.

The tubular part of the nephron is usually divided into four sections:

1) main (proximal);

2) a thin segment of the loop of Henle;

3) distal;

4) collecting tubes.

Main (proximal) department consists of sinuous and straight parts. Cells of the convoluted part have a more complex structure than the cells of other parts of the nephron. These are tall (up to 8 μm) cells with a brush border, intracellular membranes, a large number of correctly oriented mitochondria, well-developed lamellar complex and endoplasmic reticulum, lysosomes, and other ultrastructures (Fig. 1). Their cytoplasm contains many amino acids, basic and acidic proteins, polysaccharides and active SH-groups, highly active dehydrogenases, diaphorases, hydrolases [Serov VV, Ufimtseva AG, 1977; Jakobsen N., Jorgensen F. 1975].

Rice. 1. Scheme of the ultrastructure of tubular cells of various parts of the nephron. 1 - cell of the convoluted part of the main section; 2 - cell of the direct part of the main section; 3 - cell of the thin segment of the loop of Henle; 4 - cell of the direct (ascending) part of the distal section; 5 - cell of the convoluted part of the distal section; 6 - "dark" cell of the connecting section and the collecting duct; 7 - "light" cell of the connecting section and the collecting duct.

Cells of the direct (descending) part of the main section they basically have the same structure as the cells of the convoluted part, but the finger-like outgrowths of the brush border are coarser and shorter, there are fewer intracellular membranes and mitochondria, they are not so strictly oriented, and they are much smaller than cytoplasmic granules.

The brush border consists of numerous finger-like outgrowths of the cytoplasm covered with a cell membrane and glycocalyx. Their number on the cell surface reaches 6500, which increases the working area of ​​each cell by 40 times. This information gives an idea of ​​the surface on which the exchange takes place in the proximal tubule. The activity of alkaline phosphatase, ATPase, 5-nucleotidase, aminopeptidase and a number of other enzymes has been proven in the brush border. The brush border membrane contains a sodium dependent transport system. It is believed that the glycocalyx covering the microvilli of the brush border is permeable to small molecules. Large molecules enter the tubule by pinocytosis, which is mediated by crater-like depressions in the brush border.

Intracellular membranes are formed not only by the BM bends of the cell, but also by the lateral membranes of neighboring cells, which seem to overlap each other. Intracellular membranes are essentially intercellular, which serves as an active transport of fluid. In this case, the main importance in transport is given to the basal labyrinth formed by protrusions of the BM into the cell; it is regarded as a "single diffusion space".

Numerous mitochondria are located in the basal part between intracellular membranes, which creates the impression of their correct orientation. Each mitochondrion is thus enclosed in a chamber formed by folds of intra- and intercellular membranes. This allows the products of enzymatic processes developing in mitochondria to easily go outside the cell. The energy produced in the mitochondria serves both the transport of matter and secretion, carried out with the help of a granular endoplasmic reticulum and a lamellar complex, which undergoes cyclic changes in various phases of diuresis.

The ultrastructure and enzyme chemistry of the cells of the tubules of the main section explain its complex and differentiated function. The brush border, like the labyrinth of intracellular membranes, is a kind of adaptation for the colossal reabsorption function performed by these cells. Enzymatic transport system of the brush border, dependent on sodium, provides reabsorption of glucose, amino acids, phosphates [Natochin Yu. V., 1974; Kinne R., 1976]. With intracellular membranes, especially with the basal labyrinth, the reabsorption of water, glucose, amino acids, phosphates and a number of other substances is associated, which is performed by the sodium-independent transport system of the labyrinth membranes.

Of particular interest is the question of tubular protein reabsorption. It is considered proven that all protein filtered in the glomeruli is reabsorbed in the proximal tubule, which explains its absence in the urine of a healthy person. This position is based on many studies performed, in particular, using an electron microscope. Thus, protein transport in the cell of the proximal tubule was studied in experiments with microinjection of labeled ¹³¹I albumin directly into the rat tubule followed by electron microscopic radiography of this tubule.

Albumin is found primarily in invaginates of the brush border membrane, then in pinocytic vesicles that merge into vacuoles. The protein from the vacuoles then appears in the lysosomes and the lamellar complex (Fig. 2) and is cleaved by hydrolytic enzymes. Most likely, the “main efforts” of high dehydrogenase, diaphorase and hydrolase activity in the proximal tubule are aimed at protein reabsorption.

Rice. 2. Scheme of protein reabsorption by the cell of the tubules of the main section.

I - micropinocytosis at the base of the brush border; Mvb - vacuoles containing ferritin protein;

II - vacuoles filled with ferritin (a) move to the basal part of the cell; b - lysosome; c - fusion of the lysosome with the vacuole; d - lysosomes with incorporated protein; AG - plate complex with tanks containing CF (painted black);

III - isolation through BM of low molecular weight fragments of reabsorbed protein formed after "digestion" in lysosomes (shown by double arrows).

In connection with these data, the mechanisms of "damage" to the tubules of the main department become clear. In NS of any genesis, proteinuric conditions, changes in the epithelium of the proximal tubules in the form of protein dystrophy (hyaline-droplet, vacuolar) reflect the resorption insufficiency of the tubules in conditions of increased porosity of the glomerular filter for protein [Davydovsky IV, 1958; Serov V.V., 1968]. There is no need to see primary dystrophic processes in tubular changes in NS.

Equally, proteinuria cannot be considered as the result of only an increased porosity of the glomerular filter. Proteinuria in nephrosis reflects both primary damage to the kidney filter and secondary depletion (blockade) of the enzymatic systems of the tubules that reabsorb the protein.

With a number of infections and intoxications, the blockade of the enzyme systems of the cells of the tubules of the main section can occur acutely, since these tubules are the first to be exposed to toxins and poisons when they are eliminated by the kidneys. Activation of hydrolases of the lysosomal apparatus of the cell in some cases completes the dystrophic process by the development of cell necrosis (acute nephrosis). In the light of the above data, the pathology of "falling out" of the enzymes of the tubules of the kidneys of a hereditary order (the so-called hereditary tubular fermentopathy) becomes clear. A certain role in the damage to the tubules (tubulolysis) is assigned to antibodies that react with the antigen of the tubular basement membrane and brush border.

Cells of the thin segment of the loop of Henle are characterized by the feature that intracellular membranes and plates cross the cell body to its entire height, forming gaps up to 7 nm wide in the cytoplasm. It seems that the cytoplasm consists of separate segments, and part of the segments of one cell, as it were, is wedged between the segments of the neighboring cell. The enzymatic chemistry of the thin segment reflects the functional feature of this section of the nephron, which, as an additional device, reduces the filtration charge of water to a minimum and ensures its “passive” resorption [Ufimtseva A. G., 1963].

The subordinate work of the thin segment of the loop of Henle, tubules of the straight part of the distal section, collecting ducts and direct vessels of the pyramids provides osmotic concentration of urine based on a countercurrent multiplier. New ideas about the spatial organization of the countercurrent-multiplier system (Fig. 3) convince us that the concentrating activity of the kidney is ensured not only by the structural and functional specialization of various parts of the nephron, but also by the highly specialized interposition of tubular structures and vessels of the kidney [Perov Yu. L., 1975 ; Kriz W., Lever A., ​​1969].

Rice. 3. Scheme of the location of the structures of the countercurrent-multiplier system in the medulla of the kidney. 1 - arterial direct vessel; 2 - venous direct vessel; 3 - thin segment of the loop of Henle; 4 - direct part of the distal section; ST - collecting ducts; K - capillaries.

Distal tubules consists of straight (ascending) and convoluted parts. The cells of the distal region are ultrastructurally similar to the cells of the proximal region. They are rich in cigar-shaped mitochondria that fill the spaces between intracellular membranes, as well as cytoplasmic vacuoles and granules around the nucleus located apically, but lack a brush border. The epithelium of the distal section is rich in amino acids, basic and acidic proteins, RNA, polysaccharides and reactive SH-groups; it is characterized by high activity of hydrolytic, glycolytic enzymes and enzymes of the Krebs cycle.

The complexity of the distal tubule cells, the abundance of mitochondria, intracellular membranes and plastic material, high enzymatic activity indicate the complexity of their function - facultative reabsorption aimed at maintaining the constancy of the physicochemical conditions of the internal environment. Facultative reabsorption is regulated mainly by the hormones of the posterior pituitary gland, adrenal glands and JGA of the kidney.

The place of action of the pituitary antidiuretic hormone (ADH) in the kidney, the "histochemical springboard" of this regulation, is the hyaluronic acid-hyaluronidase system, which is located in the pyramids, mainly in their papillae. Aldosterone, according to some reports, and cortisone affect the level of distal reabsorption by direct inclusion in the enzyme system of the cell, which ensures the transfer of sodium ions from the lumen of the tubule to the interstitium of the kidney. Of particular importance in this process belongs to the epithelium of the direct part of the distal section, and the distal effect of the action of aldosterone is mediated by the secretion of renin, which is attached to the JGA cells. Angiotensin, formed under the action of renin, not only stimulates the secretion of aldosterone, but also participates in the distal reabsorption of sodium.

In the convoluted part of the distal tubule, where it approaches the pole of the vascular glomerulus, macula densa is distinguished. Epithelial cells in this part become cylindrical, their nuclei become hyperchromic; they are located in a polysade-like manner, and there is no continuous basement membrane here. Macula densa cells have close contacts with granular epithelioid cells and JGA lacis cells, which ensures the influence of the chemical composition of the urine of the distal tubule on glomerular blood flow and, conversely, the hormonal effects of JGA on macula densa.

To some extent, their selective damage in acute hemodynamic kidney damage is associated with the structural and functional feature of the distal tubules, their increased sensitivity to oxygen starvation, in the pathogenesis of which the main role is played by deep violations of the renal circulation with the development of anoxia of the tubular apparatus. In conditions of acute anoxia, the cells of the distal tubules are exposed to acidic urine containing toxic products, which leads to their damage up to necrosis. In chronic anoxia, the cells of the distal tubule more often than the proximal one undergo atrophy.

Collecting tubes, lined with cubic, and in the distal sections with a cylindrical epithelium (light and dark cells) with a well-developed basal labyrinth, highly permeable to water. The secretion of hydrogen ions is associated with dark cells, high activity of carbonic anhydrase was found in them [Zufarov K. A. et al., 1974]. Passive transport of water in the collecting tubes is ensured by the features and functions of the countercurrent multiplying system.

Finishing the description of the histophysiology of the nephron, one should dwell on its structural and functional differences in different parts of the kidney. On this basis, cortical and juxtamedullary nephrons are distinguished, differing in the structure of the glomeruli and tubules, as well as the originality of their function; the blood supply to these nephrons is also different.

Clinical Nephrology

ed. EAT. Tareeva

renal corpuscle

Diagram of the structure of the renal corpuscle

Types of nephrons

There are three types of nephrons - cortical nephrons (~85%) and juxtamedullary nephrons (~15%), subcapsular.

1. The renal corpuscle of the cortical nephron is located in the outer part of the cortex (outer cortex) of the kidney. The loop of Henle in most cortical nephrons is short and lies within the outer medulla of the kidney.
2. The renal corpuscle of the juxtamedullary nephron is located in the juxtamedullary cortex, near the border of the renal cortex with the medulla. Most juxtamedullary nephrons have a long loop of Henle. Their loop of Henle penetrates deep into the medulla and sometimes reaches the tops of the pyramids.
3. Subcapsular are located under the capsule.

glomerulus

The glomerulus is a group of highly fenestrated (fenestrated) capillaries that receive their blood supply from an afferent arteriole. They are also called the magic net (lat. rete mirabilis), since the gas composition of the blood passing through them is slightly changed at the outlet (these capillaries are not directly intended for gas exchange). The hydrostatic pressure of the blood creates a driving force to filter fluid and solutes into the lumen of Bowman-Shumlyansky's capsule. The unfiltered part of the blood from the glomeruli enters the efferent arteriole. The efferent arteriole of the superficially located glomeruli breaks up into a secondary network of capillaries that wrap around the convoluted tubules of the kidneys, the efferent arterioles from the deeply located (juxtamedullary) nephrons continue into the descending direct vessels (lat. vasa recta) descending into the renal medulla. Substances reabsorbed in the tubules then enter these capillary vessels.

Bowman-Shumlyansky capsule

The structure of the proximal tubule

The proximal tubule is built of high columnar epithelium with strongly pronounced microvilli of the apical membrane (the so-called "brush border") and interdigitations of the basolateral membrane. Both microvilli and interdigitations significantly increase the surface of cell membranes, thereby enhancing their resorptive function.

The cytoplasm of the cells of the proximal tubule is saturated with mitochondria, which are located to a greater extent on the basal side of the cells, thereby providing the cells with the energy necessary for the active transport of substances from the proximal tubule.

Transport processes

Loop of Henle

Links

• Life in spite of Chronic Kidney Failure. Website: A. Yu. Denisova

The complex structure of the kidneys ensures the performance of all their functions. The main structural and functional unit of the kidney is a special formation - the nephron. It consists of glomeruli, tubules, tubules. In total, a person has from 800,000 to 1,500,000 nephrons in the kidneys. A little more than a third are constantly involved in the work, the rest provide a reserve for emergencies, and are also included in the blood purification process to replace the dead.

How it works

Due to its structure, this structural and functional unit of the kidney can provide the entire process of blood processing and urine formation. It is at the level of the nephron that the kidney performs its main functions:

• filtering blood and removing decay products from the body;
• maintaining water balance.

This structure is located in the cortical substance of the kidney. From here, it first descends into the medulla, then again returns to the cortical and passes into the collecting ducts. They merge into common ducts that open into the renal pelvis, and give rise to the ureters, which carry urine out of the body.

The nephron begins with the renal (Malpighian) body, which consists of a capsule and a glomerulus located inside it, consisting of capillaries. The capsule is a bowl, it is called by the name of the scientist - the Shumlyansky-Bowman capsule. The capsule of the nephron consists of two layers, the urinary tubule emerges from its cavity. At first, it has a convoluted geometry, and at the border of the cortical and medulla of the kidneys, it straightens. Then it forms the loop of Henle and again returns to the renal cortical layer, where it again acquires a convoluted contour. Its structure includes convoluted tubules of the first and second order. The length of each of them is 2-5 cm, and taking into account the number, the total length of the tubules will be about 100 km. Thanks to this, the huge work that the kidneys do becomes possible. The structure of the nephron allows you to filter the blood and maintain the required level of fluid in the body.

Components of the nephron

• Capsule;
• Glomerulus;
• Convoluted tubules of the first and second order;
• Ascending and descending parts of the loop of Henle;
• collecting ducts.

Why do we need so many nephrons

The nephron of the kidney is very small, but their number is large, which allows the kidneys to cope with their tasks with high quality even in difficult conditions. It is thanks to this feature that a person can live quite normally with the loss of one kidney.

Modern studies show that only 35% of units are directly engaged in “business”, the rest are “resting”. Why does the body need such a reserve?

Firstly, an emergency situation may arise, which will lead to the death of part of the units. Then their functions will be taken over by the remaining structures. This situation is possible with diseases or injuries.

Secondly, their loss occurs with us all the time. With age, some of them die due to aging. Until the age of 40, the death of nephrons in a person with healthy kidneys does not occur. Further, we lose about 1% of these structural units every year. They cannot regenerate, it turns out that by the age of 80, even with a favorable state of health in the human body, only about 60% of them function. These figures are not critical, and allow the kidneys to cope with their functions, in some cases completely, in others there may be slight deviations. The threat of kidney failure lies in wait for us when there is a loss of 75% or more. The remaining amount is not enough to ensure normal blood filtration.

Such severe losses can be caused by alcoholism, acute and chronic infections, injuries to the back or abdomen that cause damage to the kidneys.

Varieties

It is customary to distinguish different types of nephrons depending on their characteristics and the location of the glomeruli. Most of the structural units are cortical, about 85% of them, the remaining 15% are juxtamedullary.

Cortical are subdivided into superficial (superficial) and intracortical. The main feature of surface units is the location of the renal corpuscle in the outer part of the cortical substance, that is, closer to the surface. In intracortical nephrons, the renal corpuscles are located closer to the middle of the cortical layer of the kidney. In juxtamedullary malpighian bodies are deep in the cortical layer, almost at the beginning of the brain tissue of the kidney.

All types of nephrons have their own functions associated with structural features. So, cortical ones have a fairly short loop of Henle, which can penetrate only the outer part of the renal medulla. The function of cortical nephrons is the formation of primary urine. That is why there are so many of them, because the amount of primary urine is about ten times greater than the amount excreted by a person.

Juxtamedullary have a longer loop of Henle and are able to penetrate deep into the medulla. They affect the level of osmotic pressure, which regulates the concentration of the final urine and its quantity.

How nephrons work

Each nephron consists of several structures, the coordinated work of which ensures the performance of their functions. The processes in the kidneys are ongoing, they can be divided into three phases:

1. filtration;
2. reabsorption;
3. secretion.

The result is urine, which is secreted into the bladder and excreted from the body.

The mechanism of operation is based on filtering processes. In the first stage, primary urine is formed. It does this by filtering the blood plasma in the glomerulus. This process is possible due to the difference in pressure in the membrane and in the glomerulus. Blood enters the glomeruli and is filtered there through a special membrane. The filtration product, that is, the primary urine, enters the capsule. Primary urine is similar in composition to blood plasma, and the process can be called pre-treatment. It consists of a large amount of water, it contains glucose, excess salts, creatinine, amino acids and some other low molecular weight compounds. Some of them will remain in the body, some will be removed.

If we take into account the work of all active kidney nephrons, then the filtration rate is 125 ml per minute. They work constantly, without interruptions, so during the day a huge amount of plasma passes through them, resulting in the formation of 150-200 liters of primary urine.

The second phase is reabsorption. Primary urine undergoes further filtration. This is necessary to return the necessary and useful substances contained in it to the body:

• water;
• salts;
• amino acids;
• glucose.

Stories from our readers

“I was able to cure the KIDNEYS with the help of a simple remedy, which I learned about from an article by a UROLOGIST with 24 years of experience Pushkar D.Yu ...”

The main role at this stage is played by the proximal convoluted tubules. There are villi inside them, which significantly increase the suction area, and, accordingly, its speed. Primary urine passes through the tubules, as a result, most of the fluid returns to the blood, about a tenth of the amount of primary urine remains, that is, about 2 liters. The entire process of reabsorption is provided not only by the proximal tubules, but also by the loops of Henle, distal convoluted tubules and collecting ducts. Secondary urine does not contain substances necessary for the body, but urea, uric acid and other toxic components that must be removed remain in it.

Normally, none of the nutrients the body needs should leave with urine. All of them return to the blood in the process of reabsorption, some partially, some completely. For example, glucose and protein in a healthy body should not be contained in the urine at all. If the analysis shows even their minimum content, then something is unfavorable with health.

The final stage of work is tubular secretion. Its essence is that hydrogen, potassium, ammonia and some harmful substances in the blood enter the urine. It can be drugs, toxic compounds. By tubular secretion, harmful substances are removed from the body, and the acid-base balance is maintained.

As a result of passing through all the phases of processing and filtration, urine accumulates in the renal pelvis to be excreted from the body. From there, it passes through the ureters to the bladder and is removed.

Thanks to the work of such small structures as neurons, the body is cleansed of the products of processing of substances that have entered it, of toxins, that is, of everything that it does not need or is harmful. Significant damage to the nephron apparatus leads to disruption of this process and poisoning of the body. The consequences may be renal failure, which requires special measures. Therefore, any manifestations of kidney dysfunction are a reason to consult a doctor.

Tired of dealing with kidney disease?

Swelling of the face and legs, PAIN in the lower back, PERMANENT weakness and fatigue, painful urination? If you have these symptoms, then there is a 95% chance of kidney disease.

If you care about your health, then read the opinion of a urologist with 24 years of experience. In his article, he talks about capsules RENON DUO.

This is a fast-acting German kidney repair remedy that has been used all over the world for many years. The uniqueness of the drug is:

• Eliminates the cause of pain and brings the kidneys to their original state.
• German capsules eliminate pain already in the first course of use, and help to completely cure the disease.
• There are no side effects and no allergic reactions.