The complex structure of the kidneys ensures that all their functions are performed. The main structural and functional unit of the kidney is a special formation - the nephron. It consists of glomeruli, tubules, and tubes. 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 work, the rest provide a reserve for emergencies, and are also included in the blood purification process to replace the dead.
Due to its structure, this structural and functional unit of the kidney can ensure 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 waste products from the body;
- maintaining water balance.
This structure is located in the renal cortex. From here it first descends into the medulla, then returns to the cortex and passes into the collecting ducts. They merge into common ducts that exit into the renal pelvis, and give rise to the ureters, through which urine is removed from the body.
The nephron begins with the renal (Malpighian) corpuscle, 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 nephron capsule consists of two layers, and the urinary tubule emerges from its cavity. At first it has a convoluted geometry, but at the border of the cortex and medulla of the kidneys it straightens. It then forms a loop of Henle and returns to the renal cortex, 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 enormous 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 in size, but their number is large, this allows the kidneys to efficiently cope with their tasks even in difficult conditions. It is thanks to this feature that a person can live completely normally with the loss of one kidney.
Modern research shows that only 35% of units are directly involved in “business”, the rest are “resting”. Why does the body need such a reserve?
Firstly, an emergency situation may arise that will lead to the death of some units. Then their functions will be taken over by the remaining structures. This situation is possible in case of illness or injury.
Secondly, their loss happens to us all the time. With age, some of them die due to aging. Until the age of 40, nephron death does not occur in a person with healthy kidneys. 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, only about 60% of them function in the human body. These numbers 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 awaits us when a loss of 75% or more occurs. The remaining amount is not enough to ensure normal blood filtration.
Such serious losses can be caused by alcoholism, acute and chronic infections, back or abdominal injuries that cause kidney damage.
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, approximately 85% of them, the remaining 15% are juxtamedullary.
Cortical ones are divided into superficial (superficial) and intracortical. The main feature of the superficial units is the location of the renal corpuscle in the outer part of the cortex, that is, closer to the surface. In intracortical nephrons, the renal corpuscles are located closer to the middle of the renal cortex. In juxtamedullaries, the Malpighian corpuscles 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. Thus, the cortical ones have a rather short loop of Henle, which can only penetrate 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 influence the level of osmotic pressure, which regulates the concentration of final urine and its quantity.
How do nephrons work?
Each nephron consists of several structures, the coordinated work of which ensures the performance of their functions. Processes in the kidneys are ongoing; they can be divided into three phases:
- filtration;
- reabsorption;
- secretion.
The result is urine, which is released into the bladder and excreted from the body.
The operating mechanism is based on filtration processes. At the first stage, primary urine is formed. This occurs 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, primary urine, enters the capsule. Primary urine is similar in composition to blood plasma, and the process can be called pre-purification. 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 nephrons of the kidneys, the filtration rate is 125 ml per minute. They work constantly, without breaks, 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 beneficial substances contained in it to the body:
- water;
- salts;
- amino acids;
- glucose.
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The proximal convoluted tubule plays the main role at this stage. 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 liquid returns back to the blood, leaving about a tenth of the amount of primary urine, that is, about 2 liters. The entire reabsorption process is ensured 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 be lost in the urine. All of them return to the blood during the process of reabsorption, some partially, some completely. For example, glucose and protein in a healthy body should not be contained in urine at all. If the analysis shows even their minimal content, it means something is wrong with your health.
The final stage of work is tubular secretion. Its essence is that hydrogen, potassium, ammonia and some harmful substances present in the blood enter the urine. These could be medications, toxic compounds. Through tubular secretion, harmful substances are removed from the body and the acid-base balance is maintained.
As a result of all phases of processing and filtration, urine accumulates in the renal pelvis and must be excreted from the body. From there it passes through the ureters into 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 entering it, of toxins, that is, of everything that is unnecessary or harmful. Significant damage to the nephron apparatus leads to disruption of this process and poisoning of the body. The consequences may be kidney failure, which requires special measures. Therefore, any manifestations of kidney problems are a reason to consult a doctor.
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Nephron- This is the functional unit of the kidney in which blood filtration and urine production occur. It consists of a glomerulus, where blood is filtered, and convoluted tubules, where urine formation is completed. The renal corpuscle consists of a renal glomerulus, in which blood vessels are intertwined, surrounded by a funnel-shaped double membrane - such a renal glomerulus is called Bowman's capsule - it continues with the renal tubule.
The glomerulus contains branches of vessels coming from the afferent artery, which carries blood to the renal corpuscles. Then these branches unite, forming the efferent arteriole, in which already purified blood flows. Between the two layers of Bowman's capsule surrounding the glomerulus, there remains a small lumen - the urinary space, which contains primary urine. A continuation of Bowman's capsule is the renal tubule - a duct consisting of segments of various shapes and sizes, surrounded by blood vessels, in which primary urine is purified and secondary urine is formed.
So, based on the above, we will try to more accurately describe kidney nephron according to the pictures located below to the right of the text.
Rice. 1. Nephron is the main functional unit of the kidney, in which the following parts are distinguished:
renal corpuscle, represented by the glomerulus (K), surrounded by Bowman's capsule (BC);
renal tubule, consisting of a proximal (PC) tubule (gray), a thin segment (TS) and a distal tubule (DC) (white).
The proximal tubule is divided into the proximal convoluted (PIC) and proximal straight tubule (NIT). In the cortex, the proximal tubules form tightly grouped loops around the renal corpuscles and then penetrate the medullary rays and continue into the medulla. In its depth, the proximal medullary tubule narrows sharply, and the thin segment (TS) of the renal tubule begins from this point. The thin segment descends deeper into the medulla, with different segments penetrating to varying depths, then turns to form a hairpin loop and returns to the cortex, abruptly becoming the distal straight tubule (DTC). From the medulla, this tubule passes through the medullary ray, then leaves it and enters the cortical labyrinth in the form of the distal convoluted tubule (DCT), where it forms loosely grouped loops around the renal corpuscle: in this area the epithelium of the tubule is transformed into the so-called macula densa (see . arrowhead) juxtaglomerular apparatus.
The proximal and distal straight tubules and thin segment form a very characteristic structure nephron kidney - loop of Henle. It consists of a thick descending portion (i.e., the proximal straight tubule), a thin descending portion (i.e., the descending portion of the thin segment), a thin ascending portion (i.e., the ascending portion of the thin segment), and a thick ascending portion. Loops of Henle penetrate to different depths into the medulla, the division of nephrons into cortical and juxtamedullary depends on this.
There are about 1 million nephrons in the kidney. If you pull it out kidney nephron in length, it will be equal to 2-3 cm depending on the length loops of Henle.
Short connecting portions (SU) connect the distal tubules to the straight collecting ducts (not shown here).
The afferent arteriole (ArA) enters the renal corpuscle and divides into glomerular capillaries, which together form the glomerulus, glomerulus. The capillaries then unite to form the efferent arteriole (EnA), which then divides into the peritubular capillary network (TCR), which surrounds the convoluted tubules and continues into the medulla, supplying it with blood.
Rice. 2. The epithelium of the proximal tubule is single-layered cubic, consisting of cells with a centrally located round nucleus and a brush border (BB) at their apical pole.
Rice. 3. The epithelium of the thin segment (TS) is formed by a single layer of very flat epithelial cells with a nucleus protruding into the lumen of the tubule.
Rice. 4. The distal tubule is also lined with a single-layer epithelium formed by cubic light cells lacking a brush border. The internal diameter of the distal tubule is nevertheless larger than that of the proximal tubule. All tubules are surrounded by a basal membrane (BM).
At the end of the article, I would like to note that there are two types of nephrons, more about this in the article "
The anatomical features that ensure the structure and functions of the nephron guarantee a complete process of urine formation from plasma. It works like a well-oiled machine due to the fact that it is very complex. During the filtering of blood plasma from formed elements, primary urine is formed, a huge part of which is subsequently absorbed back into the body.
The nephron is an important part of the kidney tissue, which ensures the process of filtering urine from the blood plasma.
What it is?
The nephron is the main structural and functional unit of renal tissue, which is involved in the process of filtration and reabsorption of urine. Scientists have proven that the portion of functioning cellular units in the parenchyma is only 35%, and the rest is a reserve in case of disease and damage to the organ. The remaining nephrons are activated only in an emergency situation, when it is necessary to cope with a large volume of work.
With age, the number of nephrons capable of functioning decreases significantly.
Structure of the renal body
On the outside, each of the elements is covered with a capsule, inside of which there is a renal glomerulus, represented by the smallest vessels, which are a branch of the renal artery. The morphofunctional unit provides blood supply with two arterial vessels. In the capillaries of the glomeruli, the formation of primary urine occurs through filtration. Between the glomerulus and the choroid plexus there is a slit-like space that continues into the nephron tubules. Filtration of blood in the kidneys occurs directly in the renal corpuscle. The structure of the nephron defines 3 sections of convoluted renal tubules, which are located outside the capsule. Here the processes of absorption of substances necessary for the body from primary urine occur.
How does it work?
The structure of the kidney nephron determines its functional significance. Thus, the renal glomerulus consists of many structures involved in the filtration process with the formation of primary urine. It is constructed with the help of a large number of small capillaries, where the blood plasma is impregnated, while the formed elements remain in the vessels. Due to the constant change in pressure in this filter, its operating speed varies. The inner layer contains podocytes, they are located on the basement membrane. Their job is to form a negative charge and prevent the passage of albumin.
All formations in the nephron are surrounded by mesangium, which carries out restoration and provides nutrition to cellular structures. It is represented by loose connective tissue. The primary filtered urine from the median fissure enters the proximal tubule. Here the suction process begins with the help of long fibers, which increase the working area. Thanks to them, water and sodium return to the body. This structure also secretes hormones into the urine that are involved in regulating blood pressure and calcium levels in the blood.
The next structural unit of the kidney is the loop of Henle (descending and ascending sections). With its help, the reuptake of sodium, chlorine and potassium occurs. The distal tubule contains energy reserves, allowing the renal corpuscle to function. Next, a collecting duct is formed that carries urine outside the microscopic organ. The function of the kidney tubules is to reverse reabsorption of all the components necessary for the body. Thanks to them, the final formation of urine occurs.
Types of structural units
Nephrons are distributed throughout the renal cortex, performing specific functions. Depending on the location, size of the nephrons and the structure they have, their types are distinguished.
Nephron capsule (Bowman-Shunlyansky capsule)
Proximal convoluted tubule
Proximal straight tubule
Loop of Henle
Descending department (thin)
Kneaded loops
Ascending department (distal straight tubule)
Distal convoluted tubule
In the center:
Brain matter
There are three types of nephrons
True cortical nephrons (1%) - all sections lie in the cortex
Intermediate nephrons (79%) – the lemniscus is immersed in the medulla, and the rest lie in the cortex
Juxta-medullary (peri-cerebral) (20%) - their loop lies entirely in the medulla, the remaining sections are located on the border between the cortex and medulla.
Function of the first two nephrons: participation in urine formation.
Function of the third nephron: acts as a shunt during heavy physical activity, dumps a larger volume of blood and performs an endocrine function.
Blood supply to nephrons
It is divided into:
1.Cardical (cortical) – blood supply to 1.2 nephrons
2. Juxto-medullary - blood supply to 3 nephrons
Blood supply of cardinal nephrons:
The portal of the kidney includes the renal artery, then the interlobar, then the arcuate (located on the border between the cortex and medulla), then the interlobular, then the afferent arteriole, which approaches the nephron capsule, then the choroid glomerulus formed by a network of capillaries (miraculous network), then the efferent arteriole, then the secondary network of capillaries, then the outflow of blood. From the subcapsular part, the blood collects in the stellate vein, from which the interlobular vein arises. From the rest of the cortex, the venules open into the interlobular vein, from which the arcuate vein, interlobular vein and renal vein. The afferent and efferent arterioles are of different diameters, the efferent arterioles are smaller than the afferent arteriole. The pressure difference in the arterioles causes high pressure in the glomerulus (70-90 mm Hg). the secondary set of capillaries entwines the renal tubules and has low blood pressure (10-12 mmHg).
Features of the blood supply to juxta-medullary nephrons:
1. The afferent and efferent arterioles are of the same diameter, so the pressure in the glomerulus is not high, and the filtration process is not possible.
2. The efferent arteriole forms a secondary network of capillaries and a direct artery, which goes into 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 the direct vein coming from the medulla, then the arcuate vein, then the interlobar and renal vein.
The structure of the nephron sections and the process of urine formation:
There are three phases in the process of urine formation:
Filtration (formation of primary urine) - the filtration process occurs in the renal corpuscle, which consists of a nephron capsule and a glomerulus. The vascular glomerulus is formed by 50-100 capillaries, arranged in the form of loops. The nephron capsule looks like a double-walled bowl, it contains:
The outer leaf is formed by a single-layer squamous epithelium, turning into cubic.
The inner layer is formed by podocyte cells. Podocyte cells have a flattened shape, their anucleate part forms outgrowths - cytotrabeculae, from which cytopogia extend. The cells are located on a three-layer basement membrane. In the basement membrane, the outer and inner layers are light, they contain few collagen fibers, but a lot of amorphous substance. The middle layer of the membrane is dark, consists of bundles of collagen fibers that are arranged in an unordered manner and form a network. The diameter of the cells is constant and equal to 7 nm (this basement membrane has selective permeability). Finestrated endothelium is adjacent to the same basement membrane on the capillary side. Podocyte cells, a three-layered basement membrane and finestrated 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 caused by the pressure difference between the high pressure in the glomerulus and the low pressure in the capsule cavity (due to the difference in pressure between the afferent and efferent arterioles).
A slit-like cavity between them
Reabsorption
Acidification
Primary urine enters the proximal tubule, this is a tube with a diameter of 50 microns, the wall contains: single-layer cubic or low prismatic epithelium, the cells have microvilli forming a border in the apical part, and basal striations in the basal part (plasmalemma folds and mitochondria). It has round nuclei and pinocytotic vesicles. Through the wall of the proximal tubule, glucose, amino acids, which are formed after the breakdown of low molecular weight proteins, and some electrolytes enter the blood. The microvilli will have alkaline-phosphotase. This is a mandatory process and will depend on the concentration of substances in the blood. The process is called obligate re-absorption. Next comes the process facultative re-absorption.
They carry out a large amount of useful functional work in the body, without which we cannot imagine our lives. The main one is the elimination of excess water and final metabolic products from the body. This happens in the smallest structures of the kidney - nephrons.
In order to move on to the smallest units of the kidney, you need to disassemble its general structure. If you look at a kidney in cross-section, its shape resembles a bean or bean.
A person is born with two kidneys, but, however, there are exceptions when only one kidney is present. They are located at the posterior wall of the peritoneum, at the level of the I and II lumbar vertebrae.
Each bud weighs approximately 110-170 grams, its length is 10-15 cm, width - 5-9 cm, and thickness - 2-4 cm.
The kidney has a posterior and anterior surface. The posterior surface is located in the renal bed. It resembles a large and soft bed, which is lined with the psoas muscle. But the front surface is in contact with other neighboring organs.
The left kidney communicates with the left adrenal gland, colon, and pancreas, and the right kidney communicates with the right adrenal gland, large and small intestines.
Leading structural components of the kidney:
- The renal capsule is its membrane. It includes three layers. The fibrous capsule of the kidney is quite thin in thickness and has a very strong structure. Protects the kidney from various damaging influences. The fat capsule is a layer of adipose tissue, which in its structure is delicate, soft and loose. Protects the kidney from shocks and impacts. The outer capsule is the renal fascia. Consists of thin connective tissue.
- Kidney parenchyma is a tissue that consists of several layers: cortex and medulla. The latter consists of 6-14 renal pyramids. But the pyramids themselves are formed from collecting ducts. Nephrons are located in the cortex. These layers are clearly distinguishable by color.
- The renal pelvis is a funnel-like depression that receives from the nephrons. It consists of cups of different sizes. The smallest ones are the calyces of the first order; urine penetrates them from the parenchyma. When small calyces unite, they form larger ones - calyxes of the second order. There are about three such calyces in the kidney. When these three calyces fuse, the renal pelvis is formed.
- The renal artery is a large blood vessel that branches off from the aorta and delivers contaminated blood to the kidney. Approximately 25% of all blood enters the kidneys every minute for cleansing. During the day, the renal artery supplies the kidney with approximately 200 liters of blood.
- Renal vein - through it, already purified blood from the kidney enters the vena cava.
The tubule emerging from the capsule is called a convoluted tubule of the first order. It's really not straight, but crooked. Passing through the medulla of the kidney, this tubule forms the loop of Henle and again turns towards the cortex. On its way, the convoluted tubule makes several turns and necessarily comes into contact with the base of the glomerulus.
A second-order tubule is formed in the cortex and flows into the collecting duct. A small number of collecting ducts join together to form excretory ducts that pass into the renal pelvis. It is these tubes, moving towards the medulla, that form the brain rays.
Types of nephrons
These types are distinguished due to the specific location of the glomeruli in the renal cortex, tubules and the characteristics of the composition and localization of blood vessels. These include:
- cortical - occupy approximately 85% of the total number of all nephrons
- juxtamedullary – 15% of the total amount
Cortical nephrons are the most numerous and also have an internal classification:
- Superficial or they are also called superficial. Their main feature is the location of the renal bodies. They are found in the outer layer of the kidney cortex. Their number is approximately 25%.
- Intracortical. Their Malpighian bodies are located in the middle part of the cortex. They predominate in number - 60% of all nephrons.
Cortical nephrons have a relatively shortened loop of Henle. Because of its small size, it is only able to penetrate the outer part of the kidney medulla.
The formation of primary urine is the main function of such nephrons.
In juxtamedullary nephrons, Malpighian bodies are found at the base of the cortex, located almost at the line of the beginning of the medulla. Their loop of Henle is longer than that of the cortical ones; it infiltrates so deeply into the medulla that it reaches the tops of the pyramids.
These nephrons in the medulla generate high osmotic pressure, which is necessary for thickening (increased concentration) and a reduction in final urine volumes to occur.
Nephron function
Their function is to form urine. This process is staged and consists of 3 phases:
- filtration
- reabsorption
- secretion
In the initial phase, primary urine is formed. In the capillary glomeruli of the nephron, the blood plasma is purified (ultrafiltered). Plasma is purified due to the difference in pressure in the glomerulus (65 mm Hg) and in the nephron membrane (45 mm Hg).
About 200 liters of primary urine are formed in the human body per day. This urine has a composition similar to blood plasma.
In the second phase, reabsorption, substances needed by the body are reabsorbed from primary urine. These substances include: water, various beneficial salts, dissolved amino acids and glucose. This occurs in the proximal convoluted tubule. Inside of which there are a large number of villi, they increase the area and speed of absorption.
From 150 liters of primary urine, only 2 liters of secondary urine are formed. It lacks important nutrients for the body, but greatly increases the concentration of toxic substances: urea, uric acid.
The third phase is characterized by the release of harmful substances into the urine that have not passed the kidney filter: various dyes, drugs, poisons.
The structure of the nephron is very complex, despite its small size. Surprisingly, almost every component of the nephron performs its own function.
Nov 7, 2016 Violetta Doctor
