Excretory system structure and functions briefly. The structure and functions of the excretory system. General characteristics of the extraction system

The amount of food that we eat in a lifetime is estimated in tens of tons, the amount of drinks consumed is of the same order of magnitude. So far, no one has burst, although there will always be jokes on this topic. The fact is that everything that enters the body goes through a complex cycle associated with grinding and chemical transformation. And it is the human excretory system that removes waste. This presentation will be short. You will need 4 pages: about the kidneys, lungs, rectum with liver, skin.

The kidneys are the body's biggest workers in excretion: 70% of all waste is excreted by them. They work with the most toxic substances that are normal in the body - the products of protein metabolism: creatinine, urea and uric acid. They also regulate the amount of fluid, salts and help get rid of foreign substances. The kidneys are securely covered on all sides: nature protects these organs of the human excretory system. If one of the kidneys is sick, the second takes over all the work.


The product of the kidneys, urine, is made from blood, although it does not have the noble reputation of the latter. Although in India even this liquid was treated with respect. There is nothing in the urine that is not in the blood. The kidneys take everything unnecessary from the blood, and leave useful substances to the body. Blood in the kidney goes through 2 stages of transformation. First, a lot is taken from it, even useful, then the necessary is sucked back. For the first process, little energy is needed, while the second is very expensive, so a small kidney consumes about 10% of all oxygen that the body has got. So much the human excretory system needs oxygen.

The more urine comes out, the thicker the blood in the vessels becomes, and vice versa. And the blood pressure directly depends on the amount of fluid in the vessels. If the pressure drops, even filtration cannot take place, and if the pressure is very high, the nephrons (functional units) will begin to fail en masse. To protect themselves, the kidneys produce renin. This hormone regulates blood pressure. Since the kidneys are in critical need of oxygen, they produce erythropoietin, which causes the bone marrow to create red blood cells - oxygen carriers. So every time you run out of breath while running, know that the kidneys are giving a signal at this time to produce red blood cells.

Urine descends into the bladder, where it accumulates until the moment when an adult decides to empty it. In a small child, this process is controlled by the spinal cord, but at the age of two, the corresponding centers of the brain mature and the child learns to use the potty. However, even an adult can lose control over the process of urination if there is more than 500 ml of urine in the bladder. You can not endure for a long time constantly: stagnation of urine and the formation of stones are possible.


If the kidneys cannot cope, many problems can be solved by the skin. It evaporates up to a liter per day. If the kidneys are sick, the sweat may smell like urine. They also secrete substances outward from the lungs - including from 400 ml of water.

The human excretory system also includes the rectum. It is associated with the liver, because most of the toxic substances of feces are obtained from bile, and the liver forms bile from substances “caught” from the blood. However, it is not easy to bring feces out - the abdominal muscles and intestines work at the same time. The rectum is emptied normally once a day, on average, about 150 g comes out of us. The kidneys excrete approximately 45 liters of urine per month. So the load on these organs is considerable.

The human excretory system works smoothly, if problems arise in one organ, others take on someone else's work. If the liver or kidneys are sick, the products of protein metabolism are excreted by the lungs and skin, but if the liver cannot cope with the waste products of hemoglobin metabolism, then the kidneys will take care of this.

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urinary system

This system consists of:

two kidneys;

Bladder;

The ureter, which connects the kidney and bladder

The urethra or urethra.

The kidneys act as filters, taking away from the blood that washes them, all metabolic products, as well as excess fluid. During the day, all the blood passes through the kidneys about 300 times. As a result, a person removes an average of 1.7 liters of urine from the body per day. Moreover, in the composition it has 3% uric acid and urea, 2% mineral salts and 95% water.

Functions of the human excretory system

1. The main function of the excretory system is to remove from the body products that it cannot absorb. If a person is deprived of kidneys, then soon he will be poisoned by various nitrogen compounds (uric acid, urea, creatine).

2. The human excretory system serves to ensure the water-salt balance, that is, to regulate the amount of salts and fluids, ensuring the constancy of the internal environment. The kidneys resist an increase in the amount of water and, thereby, an increase in pressure.

3. The excretory system monitors the acid-base balance.

4. The kidneys produce the hormone renin, which helps control blood pressure. We can say that the kidneys still carry out endocrine function.

5. The human excretory system regulates the process of "birth" of blood cells.

6. There is a regulation of the levels of phosphorus and calcium in the body.

The structure of the human excretory system

Each person has a pair of kidneys, which are located in the lumbar region on both sides of the spine. Usually one of the kidneys (right) is located just below the second. They are shaped like beans. On the inner surface of the kidney there are gates, through which the nerves and arteries enter and the lymphatic vessels, veins and ureter exit.

In the structure of the kidney, the medulla and cortex, renal pelvis and renal calyces are isolated. The nephron is the functional unit of the kidneys. Each of them has up to 1 million of these functional units. They consist of the Shumlyansky-Bowman capsule, which encloses a glomerulus of tubules and capillaries, connected, in turn, by the loop of Henle. Part of the tubules and capsules of nephrons are located in the cortex, and the remaining tubules and the loop of Henle pass into the medulla. The nephron has an abundant blood supply. The glomerulus of capillaries in the capsule forms the afferent arteriole. The capillaries gather into the efferent arteriole, which breaks up into a capillary network that wraps around the tubules.

Urination

Before being formed, urine goes through 3 stages: glomerular filtration, secretion and tubular reabsorption. Filtration takes place as follows: due to the pressure difference from human blood, water seeps into the cavity of the capsule, and with it the majority of dissolved low molecular weight substances (mineral salts, glucose, amino acids, urea, etc.) As a result of this process, primary urine appears, which has a weak concentration. During the day, the blood is filtered many times by the kidneys, with the formation of about 150-180 liters of fluid, which is called primary urine.

Urea, a number of ions, ammonia, antibiotics and other metabolic end products are additionally excreted into the urine by cells located on the walls of the tubules. This process is called secretion.

When the filtration process is over, reabsorption begins almost immediately. In this case, water is reabsorbed along with some substances dissolved in it (amino acids, glucose, many ions, vitamins). With tubular reabsorption, up to 1.5 liters of fluid (secondary urine) is formed in 24 hours. Moreover, it should not contain either proteins or glucose, but only ammonia and urea, which are toxic to the human body, which are decomposition products of nitrogenous compounds.

Urination

Urine flows through the tubules of the nephrons into the collecting ducts, through which it moves to the renal calyces and further to the renal pelvis. Then, through the ureters, it flows into a hollow organ - the bladder, which consists of muscles and holds up to 500 ml of fluid. Urine is expelled from the bladder through the urethra outside the body.

Urination is a reflex act. The stimuli of the urination center, which is located in the spinal cord (sacral region), are the stretching of the walls of the bladder and the speed of its filling.

We can say that the human excretory system is represented by a combination of many organs that are closely related to each other and complement each other's work.

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kidneys

These paired organs are located on the back wall of the abdominal cavity, on both sides of the spine. The kidney is a paired organ.

Outwardly, she has bean shape, but inside - parenchymal structure. Length one kidney no more than 12 cm, and width- from 5 to 6 cm. Normal weight kidney does not exceed 150-200 g.

Structure

The membrane that covers the outside of the kidney is called fibrous capsule. On the sagittal section, two different layers of matter can be seen. The one closest to the surface is called cortical, and the substance occupying the central position - cerebral.


They have not only an external difference, but also a functional one. On the side of the concave part are located renal hilum and pelvis, as well as ureter.

Through the renal gate, the kidney communicates with the rest of the body through the incoming renal artery and nerves, as well as the outgoing lymphatic vessels, renal vein and ureter.

The collection of these vessels is called renal pedicle. Inside the kidney are distinguished renal lobes. Each kidney has 5 pieces. The kidney lobes are separated from each other by blood vessels.

In order to clearly understand the functions of the kidneys, it is necessary to know their microscopic structure.

Number of nephrons in the kidney reaches 1 million. The nephron consists of renal corpuscle, which is located in the cortex, and tubular systems which eventually flow into the collecting duct.

The nephron also secretes 3 segments:

  • proximal,
  • intermediate,
  • distal.

Segments together with ascending and descending limbs of the loop of Henle lie in the medulla of the kidney.

Functions

Along with the main excretory function, the kidneys also provide and perform:

  • maintaining a stable level blood pH, its circulating volume in the body and the composition of the intercellular fluid;
  • thanks to metabolic function, human kidneys carry out synthesis of many substances important for the life of the organism;
  • blood formation, by producing erythrogenin;
  • the synthesis of these hormones like renin, erythropoietin, prostaglandin.

Bladder

The organ that stores urine from the ureters and out through the urethra is called bladder. This is a hollow organ that is located in the lower abdomen, just behind the pubis.

Structure

The bladder is round in shape, in which they distinguish

  • top,
  • body,
  • neck.
The latter narrows, thus passing into the urethra. When filling, the walls of the organ stretch, giving a signal about the need to empty.

When the bladder is empty, its walls thicken, and the mucous membrane gathers in folds. But there is a place that remains not wrinkled - this is a triangular area between the opening of the ureter and the opening of the urethra.

Functions

The bladder performs the following functions:

  • temporary accumulation of urine;
  • excretion of urine- the volume of urine accumulated by the bladder is 200-400 ml. Every 30 seconds, urine flows into the bladder, but the time of receipt depends on the amount of liquid drunk, temperature, and so on;
  • thanks to mechanoreceptors, which are located in the wall of the organ, controlling the amount of urine in the bladder. Their irritation serves as a signal for the contraction of the bladder and the removal of urine out.

Ureters

The ureters are thin ducts that connects the kidney and bladder. Them length is no more than 30 cm, and diameter from 4 to 7 mm.

Structure

The wall of the tube has 3 layers:

  • external (from connective tissue),
  • muscular and internal (mucous membrane).

One part of the ureter is located in the abdominal cavity, and the other in the pelvic cavity. If there are obstructions in the outflow of urine (stones), then the ureter may expand in some area up to 8 cm.

Functions

The main function of the ureter is outflow of urine accumulated in the bladder. Due to contractions of the muscular membrane, urine moves along the ureter to the bladder.

Urethra

In women and men, the urethra differs in its structure. This is due to the difference in the sex organs.

Structure

The channel itself consists of 3 shells, like the ureter. Because the female urethra shorter than in men, then women are more likely to be exposed to various diseases and inflammations of the urogenital tract.

Functions

  • In men the channel performs several functions: the excretion of urine and sperm. The fact is that the vas deferens end in the canal tube, through which the sperm flows through the canal into the glans penis.
  • Among women the urethra is a tube 4 cm long and performs only the function of excreting urine.

How is primary and secondary urine formed?

The process of urine formation includes three interrelated steps:

  • glomerular filtration,
  • tubular reabsorption,
  • tubular secretion.

First step - glomerular filtration is the process of transition of the liquid part of the plasma from the capillaries of the glomerulus into the lumen of the capsule. In the lumen of the capsule there is a filtration barrier, which contains pores in its structure that selectively let through dissimilation products and amino acids, and also prevent the passage of most proteins.

During glomerular filtration, it produces ultrafiltrate representing primary urine. It is similar to blood plasma, but contains few proteins.

The remaining 99% is returned to the blood.

Mechanism formation of secondary urine consists in the passage of the ultrafiltrate through the segments nephron and renal tubules. The walls of the tubules consist of epithelial cells, which gradually absorb back not only a large amount of water, but also all the substances necessary for the body.

The reabsorption of proteins is explained by their large size. All substances that are toxic and harmful to our body remain in the tubules, and are then excreted in the urine. This final urine is called secondary. This whole process is called tubular reabsorption.

tubular secretion called a set of processes due to which substances to be excreted from the body are secreted into the lumen of the tubules of the nephron. That is, this secretion is nothing but a reserve process of urination.

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Excretory organ system

The excretory organs include:

  • kidneys;
  • leather;
  • lungs;
  • salivary and gastric glands.

The kidneys rid a person of excess water, accumulated salts, toxins formed as a result of eating too fatty foods, toxins and alcohol. They play a significant role in the excretion of decay products of drugs. Thanks to the work of the kidneys, a person does not suffer from an overabundance of various minerals and nitrogenous substances.

Lungs - maintain oxygen balance and are both internal and external filters. They contribute to the effective removal of carbon dioxide and harmful volatile substances formed inside the body, help to get rid of liquid vapors.

Gastric and salivary glands - help to remove excess bile acids, calcium, sodium, bilirubin, cholesterol, as well as undigested food residues and metabolic products. The digestive tract organs rid the body of heavy metal salts, drug impurities, and toxic substances. If the kidneys do not cope with their task, the load on this organ increases significantly, which can affect the efficiency of its work and lead to failures.

The skin carries out the metabolic function through the sebaceous and sweat glands. Sweating removes excess water, salts, urea and uric acid, as well as about two percent of carbon dioxide. The sebaceous glands play a significant role in the protective functions of the body, releasing sebum, which consists of water and a number of unsaponifiable compounds. It does not allow harmful compounds to penetrate through the pores. The skin effectively regulates heat transfer, protecting a person from overheating.

urinary system

The main role among the excretory organs of a person is occupied by the kidneys and the urinary system, which include:

  • bladder;
  • ureter;
  • urethra.

The kidneys are a paired legume-shaped organ, about 10-12 cm long. An important excretory organ is located in the human lumbar region, protected by a dense fatty layer and somewhat mobile. That is why, it is not very susceptible to injury, but is sensitive to internal changes within the body, human nutrition and negative factors.

Each of the kidneys in an adult weighs about 0.2 kg and consists of a pelvis and the main neurovascular bundle that connects the organ to the human excretory system. The pelvis serves to communicate with the ureter, and that with the bladder. Such a structure of the urinary excretion organs allows you to completely close the circulatory cycle and effectively perform all the assigned functions.

The structure of both kidneys consists of two interconnected layers:

  • cortical - consists of glomeruli of nephrons, serves as the basis for kidney function;
  • cerebral - contains a plexus of blood vessels, supplies the body with the necessary substances.

The kidneys distill all human blood through themselves in 3 minutes, and therefore they are the main filter. If the filter is damaged, an inflammatory process or kidney failure appears, the metabolic products do not enter the urethra through the ureter, but continue their movement through the body. Toxins are partially excreted with sweat, with metabolic products through the intestines, and also through the lungs. However, they cannot completely leave the body, and therefore acute intoxication develops, which poses a threat to human life.

Functions of the urinary system

The main functions of the excretory organs are to remove toxins and excess mineral salts from the body. Since the main role of the human excretory system is played by the kidneys, it is important to understand exactly how they purify the blood and what can interfere with their normal work.

When blood enters the kidneys, it enters their cortical layer, where coarse filtration occurs due to the glomeruli of the nephron. Large protein fractions and compounds return to the human bloodstream, supplying it with all the necessary substances. Small debris is sent to the ureter to leave the body with urine.

Here, tubular reabsorption manifests itself, during which the reverse absorption of nutrients from the primary urine into the human blood occurs. Some substances are reabsorbed with a number of features. In the case of an excess of glucose in the blood, which often occurs with the development of diabetes, the kidneys cannot cope with the entire volume. Some excreted glucose may appear in the urine, which signals the development of a formidable disease.

During the processing of amino acids, it happens that at the same time in the blood there can be several subspecies carried by the same carriers. In this case, reabsorption can be inhibited and load the organ. The protein should not normally appear in the urine, but under certain physiological conditions (high temperature, hard physical work) it can be detected at the outlet in small quantities. This condition requires monitoring and control.

Thus, the kidneys in several stages completely filter the blood, leaving no harmful substances. However, due to an excess of toxins in the body, one of the processes in the urinary system may be disrupted. This is not a pathology, but it requires the advice of a specialist, since with constant overloads, the organ quickly fails, causing serious damage to human health.

In addition to filtration, the urinary system:

  • regulates the balance of fluid in the human body;
  • maintains acid-base balance;
  • takes part in all metabolic processes;
  • regulates blood pressure;
  • produces the necessary enzymes;
  • provides a normal hormonal background;
  • improves the absorption of vitamins and minerals into the body.

If the kidneys stop working, harmful fractions continue to wander through the vascular bed, increasing the concentration and leading to a slow poisoning of a person with metabolic products. That's why it's so important to keep them running smoothly.

Preventive measures

In order for the entire excretion system to work smoothly, it is necessary to carefully monitor the work of each of the organs related to it, and contact a specialist at the slightest failure. For the full functioning of the kidneys, the hygiene of the excretory organs of the urinary system is necessary. The best prevention in this case is the minimum amount of harmful substances consumed by the body. It is necessary to carefully monitor nutrition: do not drink alcohol in large quantities, reduce the content of salty, smoked, fried foods in the diet, as well as foods oversaturated with preservatives.

Other human excretory organs also need hygiene. If we talk about the lungs, then it is necessary to limit being in dusty rooms, places where pesticides accumulate, enclosed spaces with a high content of allergens in the air. You should also prevent lung diseases, conduct a fluorographic study once a year, and eliminate foci of inflammation in time.

It is equally important to maintain the normal functioning of the gastrointestinal tract. Due to insufficient production of bile or the presence of inflammatory processes in the intestines or stomach, fermentation processes may occur with the release of decay products. Getting into the blood, they cause manifestations of intoxication and can lead to irreversible consequences.

As for the skin, everything is simple here. They should be regularly cleaned of various contaminants and bacteria. However, you can't overdo it. Excessive use of soap and other detergents can disrupt the sebaceous glands and lead to a decrease in the natural protective function of the epidermis.

The excretory organs accurately recognize which cells of substances are necessary for the maintenance of all life systems, and which can be harmful. They cut off everything superfluous and remove it with sweat, exhaled air, urine and feces. If the system stops working, the person dies. Therefore, it is important to monitor the work of each organ and, if you feel worse, immediately contact a specialist for examination.

1. Through which organs are metabolic products excreted from the body? List the functions of the kidney and describe each of them.

As a result of metabolism in the human body, harmful decay products of proteins, fats and carbohydrates are formed, which cannot be used and must be removed to the external environment. Carbon dioxide is removed through the lungs, undigested food residues, as well as many medicines and harmful substances are removed from the body through the digestive system. Another organ that has the function of excretion is the Skin, in which there are sweat glands. The main organ of the system of excretion of substances from the human body is the kidney. They allow you to remove from the body excess water, salts, drugs and harmful substances that did not get into the bile, as well as protein breakdown products. The main function of the kidneys is the excretion of harmful organic substances. These include urea, which is formed during the breakdown of proteins, drugs and their transformation products in the body, and other toxic substances. The yellow color in the urine is due to the decay products of hemoglobin released from aged red blood cells. The second function is the regulation of the amount of water in the body. Water accounts for about 70% of a person's body weight. Of these, approximately 2/3 is located inside the cells, and 1/3 in the extracellular space. Extracellular water is distributed between the blood and tissue fluid. Water is excreted through various organs, primarily through the kidneys, the amount of water in the human body must be maintained at a constant level. When the water supply increases, the kidneys produce more urine, and vice versa. The third function of the kidney is the regulation of salt concentration in the body's environment. Urine is an aqueous solution, which, in addition to urea, contains salts of sodium, potassium and chlorine. The kidneys regulate the concentration of these substances in the urine, depending on how much they are ingested and contained in the blood. Thus, the kidneys play a primary role in the regulation of the body's water-salt balance, that is, in maintaining a correspondence between the intake and excretion of salts from the body. Some functions of the kidneys are not directly related to excretion. The kidneys produce hormones that regulate the formation of red blood cells and calcium metabolism in the body. Finally, the kidneys, like the liver, can produce large amounts of glucose from fats and amino acids when they are deficient in the blood.

2. What organs does the human excretory system consist of?

The excretory system consists of the kidneys and the urinary tract, which includes the ureters, bladder, and urethra.

3. How many nephrons are there in two human kidneys and what is their structure?

There are about two million nephrons in two human kidneys. Nephron - is a thin convoluted tube 35 - 40 mm long. The walls of the nephron are very thin, they are formed by a single layer of epithelial cells. The nephron begins with the Bowman's capsule, which is an extension of the blindly closed tubule of the nephron. The capsule contains a glomerulus of blood capillaries. A thin tubule of the nephron departs from the capsule, its diameter is about 0.05 mm. The tubule passes through the kidney towards the pelvis, then turns back to the cortex. The middle curved part of the nephron, which has the shape of a hairpin, is called the loop of Henle. Ultimately, the tubule of the nephron flows into the collecting duct. This tube collects urine from several nephrons and directs it to the renal pelvis.

4. What are the features of the blood supply to the kidneys?

The renal artery arises directly from the aorta. In the kidneys, it divides many times, forming thin arteries that give rise to the capillary glomeruli of the kidneys. Since the path from the aorta to the capillary glomeruli is rather short, the pressure in these capillaries is 2 times higher than in the capillaries of other organs. High pressure is required to filter fluid from the glomerular capillaries to the lumen of the Bowman's capsule. At the exit from the glomerulus, the capillaries gather into a small blood vessel, which soon branches back into the capillaries. These capillaries form a secondary capillary network, braiding the tubules of the nephron. The blood pressure in the capillaries of the secondary network, on the contrary, is lower than in many capillaries of the human body. This contributes to the flow of fluid into them, which has got from the tubules of the nephrons into the kidney tissue. Thus, the two capillary networks of the bloodstream of the kidneys not only have a different structure, but also perform completely different functions.

5. Why can kidney disease lead to anemia? (To answer this question, repeat § 20.)

Anemia in kidney disease is caused by a lack of the hormone erythropoietin, which is produced by the kidneys.

6. In what other organs, besides the kidneys, are there two series-connected capillary networks? What does this mean for the functioning of these organs?

1. Intestine and liver. Capillaries from the intestine gather into the portal vein of the liver and immediately disintegrate again into capillaries. In the liver, the blood is cleared of toxins.

2. Hypothalamus and pituitary gland. The capillaries of the hypothalamus gather into one artery, which goes directly to the pituitary gland, in which a capillary network is again formed. This is how the connected hypothalamic-pituitary system works.

The excretory organs play an important role in maintaining the constancy of the internal environment of the body by removing excess decay products, excess water and salts. In the implementation of this function, the lungs, organs of the digestive system (liver, intestines), skin, as well as a specialized urination system take part. In addition, the excretory organs provide protective (fat secretion), lactogenic (milk secretion) and pheromones (odor production) functions.

The lungs remove carbon dioxide, water vapor, volatile substances (acetone, ketones and other volatile substances) from the body.

Through the digestive system, along with undigested food products, salts of heavy metals, toxic substances, residues of the decay products of proteins, fats and carbohydrates are excreted. In the intestine, the final absorption of simplified nutrients into the blood takes place. Undigested and excess substances form fecal masses and are expelled from the body along with intestinal gases. The intestine contains a large number of bacteria that support the processes of digestion, so the violation of the microflora (dysbacteriosis) entails consequences of varying severity.

On the skin, the sweat and sebaceous glands play the excretory function, and during breastfeeding in women, the mammary glands perform the excretory function. Sweat glands remove water, salts and organic matter. Sweating is involved in thermoregulation and the removal of water from the skin and some waste products, as well as resisting the drying of the skin. In order to preserve the natural state of the skin, a protective hydrolipidic film is created.

Up to 75% of metabolic products excreted from the body are removed through the kidneys. Water, salts and protein breakdown products are excreted in the urine. Thanks to the urinary system, ammonia, urea, uric acid, poisonous and toxic substances, residues of used drugs, etc. are also removed from the body.

With the help of the kidneys, the body maintains an acid-base balance (pH), a constant, normal volume of water and salts, and a stable osmotic pressure.

The kidneys protect the human body from poisoning. Each person has two kidneys, which are located at the level of the lower back on both sides of the spine. All the blood in the body passes through the kidneys every five minutes. It brings harmful substances from the cells; In the kidneys, the blood is purified and, entering the veins, is sent back to the heart.

The value of the excretory system is as follows: release of the body from the end products of metabolism, which are toxic substances; participation in maintaining the constancy of the internal environment of the body (osmotic pressure, active blood reaction); the synthesis of biologically active substances that regulate the constancy of blood pressure and the number of blood cells (renin, erythropoietin).

Thus, the kidneys, together with other organs, ensure the constancy of the composition of the body (homeostasis). The kidneys are the main excretory organs.

1. What is the structure of the organs of the excretory system?

Organs of the urinary system: kidneys, ureters, bladder, urethra.

The kidneys are paired bean-shaped organs located in the lumbar region of the spine. The surface of the kidney is covered with a connective tissue capsule. Under the capsule are the cortex and medulla, which penetrate each other. The tops of the 2-3 pyramids of the medulla form a papilla, protruding into the small renal calyces, from which 2-3 large renal calyces are formed, from which the renal pelvis, into which urine flows. From the renal pelvis of the right and left kidneys, the ureters depart, flowing into the bladder, from which urine is excreted through the urethra.

The kidneys perform a number of functions. They are a biological filter, thanks to the release of metabolic products, the constancy of the chemical composition and properties of the internal fluids of the body (homeostasis) is maintained.

The ureter is a tube with thick muscular walls.

The bladder is a hollow muscular organ located in the pelvis. It has a rather thick wall, which, when the bladder is filled, greatly stretches and thins, the bladder capacity is up to 500 ml.

2. What is the significance of excretory processes for the body?

The significance of the excretion processes lies in the removal from the body of compounds that are not needed by the body, which are formed as a result of metabolism. Due to the removal of metabolic products, the composition of the internal environment of the body is maintained.

Basically, metabolic products are removed through the organs of the excretory system: the kidneys (where urine is formed), the ureters, and the bladder. Part of the substances is removed through the lungs, skin, partly through the intestines.

3. What is the microscopic structure of the kidneys?

The structural unit of the kidney is the nephron. There are about 1 million nephrons in each kidney. It consists of a capsule, in the deepening of which there is a tangle of capillaries and a renal tubule.

The capsule is located in the cortical layer, its wall is formed by a single-layer epithelium. A convoluted tubule of the 1st order departs from the capsule, while the cavity of the capsule passes into the lumen of the tubule. It descends into the medulla, where it forms the loop of Henle, then returns to the cortical layer, forming a convoluted tubule of the 2nd order, which flows into the collecting duct of the nephron. The collecting ducts merge to form larger excretory ducts. They pass through the medulla and open at the tops of the pyramids.

Inside the renal capsule in a kind of glass lies a capillary glomerulus. It is formed by branching of the capillaries of the renal artery. Blood enters the capillary glomerulus through the afferent arteries, and flows out through the efferent arteries. The diameter of the afferent artery is larger than that of the efferent artery. After leaving the glomerulus, the vessel branches again, forming capillaries that braid the tubules of the same nephron. The tubules also receive blood directly from the afferent arteriole, which gives a lateral branch. From the capillaries of the tubules, blood is collected in the venous plexus and then again enters the renal vein. That is, the blood that has passed through the capillary glomerulus then passes through the capillaries of the renal tubule and only then enters the veins.

4. How is urine produced?

The formation of urine occurs in 2 stages: the 1st stage is the formation of primary urine, the 2nd stage is the formation of secondary urine.

Formation of primary urine. In the capillaries of the glomerulus, fluid is filtered from the blood. Filtration is facilitated by the relatively high hydrostatic pressure of the blood flowing in the capillaries of the glomerulus. In the capillaries of the glomeruli, blood flows at a higher pressure than in other organs. The creation of high pressure in the capillary glomeruli contributes to the difference in the diameter of the vessels that bring and carry blood. The liquid formed by filtration and trapped in the capsule is called primary urine. During the day, 150-170 liters of primary urine are formed. This is filtered blood plasma, in which there are no blood cells and large protein molecules. The content of other substances corresponds to their content in blood plasma. material from the site

Formation of secondary urine. From the renal capsule, urine enters the renal tubule. There is tubular reabsorption. The thin walls of the tubule absorb water and some dissolved substances (sugar - completely, others - partially, urea - not absorbed at all). Re-absorption is carried out due to passive and active diffusion. Due to selective absorption, only those substances that are not needed by the body remain in the secondary urine. For example, the concentration of urea in secondary urine increases by more than 60 times. The necessary substances are returned to the blood through a network of capillaries that wrap around the renal tubule. In the renal tubule, some substances are released into its lumen. For example, epithelial cells secrete ammonia into the urine, some dyes, drugs such as penicillin.

1.2-1.5 liters of secondary urine is formed per day. The resulting urine flows into the renal pelvis, from it through the ureter to the bladder. Stretching of the walls of the bladder (with an increase in its volume to 200-300 ml) leads to reflex urination.

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  • kidney structure meaning briefly

During the life of the body in the tissues, the breakdown of proteins, fats and carbohydrates with the release of energy. The human excretory system rids the body of the end products of decay - water, carbon dioxide, ammonia, urea, uric acid, phosphate salts and other compounds.

From the tissues, these dissimilation products pass into the blood, are brought to the excretory organs by the blood, and through them are excreted from the body. The excretion of these substances involves the lungs, skin, digestive apparatus and organs of the urinary system.

Most of the decay products are excreted through the urinary tract. This system includes the kidneys, ureters, bladder and urethra.

Human Kidney Functions

Due to their activity in the human body, the kidneys are involved in:

  • In maintaining the constancy of the volume of body fluids, their osmotic pressure and ionic composition;
  • regulation of acid-base balance;
  • release of products of nitrogen metabolism and foreign substances;
  • savings or excretion of various organic substances (glucose, amino acids, etc.) depending on the composition of the internal environment;
  • metabolism of carbohydrates and proteins;
  • secretion of biologically active substances (hormone renin);
  • hematopoiesis.

The kidneys have a wide range of functional adaptation to the needs of the body to maintain homeostasis, since they are able to significantly vary the qualitative composition of urine, its volume, osmotic pressure and pH.

The right and left kidneys, each about 150 g, are located in the abdominal space on the sides of the spinal column at the level of the lumbar vertebrae. Outside, the kidneys are covered with a dense membrane. On the inner concave side are the "gates" of the kidney, through which the ureter, renal arteries and veins, lymphatic vessels and nerves pass. On the section of the kidney, it can be seen that it consists of two layers:

  • The outer layer, darker, is the cortex;
  • internal - medulla.

The structure of the human kidney. The structure of the nephron

The kidney has a complex structure and consists of approximately 1 million structural and functional units - nephrons, the space between which is filled with connective tissue.


Nephrons- these are complex microscopic formations that begin with a double-walled glomerular capsule (Shumlyansky-Bowman's capsule), inside which is the renal corpuscle (Malpighian corpuscle). Between the layers of the capsule is a cavity that passes into the convoluted (primary) urinary tubule. It reaches the border of the cortical and medulla of the kidney. At the border, the tubule narrows and straightens.

In the medulla of the kidney, it forms a loop and returns to the cortical layer of the kidney. Here it again becomes convoluted (secondary) and opens into the collecting duct. The collecting ducts, merging, form the common excretory ducts, which pass through the medulla of the kidney to the tops of the papillae protruding into the cavity of the pelvis. The pelvis passes into the ureter.

Urine formation

How is urine formed in the nephrons? In a simplified form, this happens as follows.

Primary urine

When blood passes through the capillaries of the glomeruli, water and substances dissolved in it are filtered from its plasma through the wall of the capillary into the cavity of the capsule, with the exception of macromolecular compounds and blood cells. Therefore, proteins with a large molecular weight do not enter the filtrate. But here come such metabolic products as urea, uric acid, ions of inorganic substances, glucose and amino acids. This filtered liquid is called primary urine.

Filtration is carried out due to the high pressure in the capillaries of the glomeruli - 60-70 mm Hg. Art., which is two or more times higher than in the capillaries of other tissues. It is created due to the different sizes of the gaps of the afferent (wide) and efferent (narrow) vessels.

During the day, a huge amount of primary urine is formed - 150-180l. Such intensive filtration is possible thanks to:

  • A large amount of blood that flows through the kidneys during the day - 1500-1800l;
  • large surface of the walls of the capillaries of the glomeruli - 1.5 m 2;
  • high blood pressure in them, which creates a filtering force, and other factors.

From the capsule of the glomerulus, the primary urine enters the primary tubule, which is densely braided with secondary branched blood capillaries. In this part of the tubule, most of the water and a number of substances are absorbed (reabsorbed) into the blood: glucose, amino acids, low molecular weight proteins, vitamins, sodium, potassium, calcium, chlorine ions.

Secondary urine

That part of the primary urine that remains at the end of the passage through the tubules is called secondary.

Consequently, in the secondary urine, during normal kidney function, there are no proteins and sugar. Their appearance there indicates a violation of the kidneys, although with excessive consumption of simple carbohydrates (over 100 g per day), sugars may appear in the urine even with healthy kidneys.

Secondary urine is formed a little - about 1.5 liters per day. The rest of the primary urine liquid from a total amount of 150-180 liters is absorbed into the blood through the cells of the walls of the urinary tubules. Their total surface is 40-50m 2 .

The kidneys do a lot of work non-stop. Therefore, with a relatively small size, they consume a lot of oxygen and nutrients, which indicates a large energy expenditure during the formation of urine. So, they consume 8-10% of all oxygen absorbed by a person at rest. More energy is expended per unit mass in the kidneys than in any other organ.

Urine is collected in the bladder. As it accumulates, its walls stretch. This is accompanied by irritation of the nerve endings located in the walls of the bladder. Signals enter the central nervous system and the person feels the urge to urinate. It is carried out through the urethra and is under the control of the nervous system.



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