Selection- a set of physiological processes aimed at removing metabolic end products from the body (carried out by the kidneys, sweat glands, lungs, gastrointestinal tract, etc.).
Excretion) - the process of liberating the body from the end products of metabolism, excess water, minerals (macro- and microelements), nutrients, foreign and toxic substances and heat. The release occurs constantly in the body, which ensures the maintenance of the optimal composition and physicochemical properties of its internal environment and, above all, blood.
The end products of metabolism (metabolism) are carbon dioxide, water, nitrogen-containing substances (ammonia, urea, creatinine, uric acid). Carbon dioxide and water are formed during the oxidation of carbohydrates, fats and proteins and are released from the body mainly in free form. A small portion of carbon dioxide is released as bicarbonates. Nitrogen-containing metabolic products are formed during the breakdown of proteins and nucleic acids. Ammonia is formed during the oxidation of proteins and is removed from the body mainly in the form of urea (25-35 g/day) after appropriate transformations in the liver and ammonium salts (0.3-1.2 g/day). In the muscles, during the breakdown of creatine phosphate, creatine is formed, which, after dehydration, is converted into creatinine (up to 1.5 g/day) and in this form is removed from the body. When nucleic acids break down, uric acid is formed.
During the oxidation of nutrients, heat is always released, the excess of which must be removed from the place of its formation in the body. These substances formed as a result of metabolic processes must be constantly removed from the body, and excess heat must be dissipated into the external environment.
Human excretory organs
The process of excretion is important for homeostasis, it ensures the release of the body from metabolic end products that can no longer be used, foreign and toxic substances, as well as excess water, salts and organic compounds received from food or formed as a result of metabolism. The main importance of the excretory organs is to maintain a constant composition and volume of fluid in the internal environment of the body, primarily blood.
Excretory organs:
- kidneys - remove excess water, inorganic and organic substances, end products of metabolism;
- lungs- remove carbon dioxide, water, some volatile substances, for example, ether and chloroform vapors during anesthesia, alcohol vapors during intoxication;
- salivary and gastric glands- release heavy metals, a number of drugs (morphine, quinine) and foreign organic compounds;
- pancreas and intestinal glands - excrete heavy metals and drugs;
- skin (sweat glands) - They secrete water, salts, some organic substances, in particular urea, and during hard work, lactic acid.
General characteristics of the extraction system
Selection system - This is a collection of organs (kidneys, lungs, skin, digestive tract) and regulatory mechanisms, the function of which is the excretion of various substances and the dissipation of excess heat from the body into the environment.
Each of the organs of the excretory system plays a leading role in removing certain excreted substances and dissipating heat. However, the efficiency of the excretion system is achieved through their joint work, which is ensured by complex regulatory mechanisms. In this case, a change in the functional state of one of the excretory organs (due to its damage, disease, exhaustion of reserves) is accompanied by a change in the excretory function of others included in the body’s integral excretory system. For example, with excessive excretion of water through the skin with increased sweating under conditions of high external temperature (in the summer or while working in hot workshops in production), the formation of urine by the kidneys and its excretion decreases - diuresis decreases. With a decrease in the excretion of nitrogenous compounds in the urine (in case of kidney disease), their removal through the lungs, skin, and digestive tract increases. This is the cause of “uremic” breath odor in patients with severe forms of acute or chronic renal failure.
Kidneys play a leading role in the excretion of nitrogen-containing substances, water (under normal conditions, more than half of its volume from the daily excretion), excess of most minerals (sodium, potassium, phosphates, etc.), excess of nutrients and foreign substances.
Lungs ensure the removal of more than 90% of carbon dioxide formed in the body, water vapor, and some volatile substances that enter or are formed in the body (alcohol, ether, chloroform, gases from vehicles and industrial enterprises, acetone, urea, surfactant degradation products). When kidney function is impaired, the secretion of urea from the secretions of the respiratory tract glands increases, the decomposition of which leads to the formation of ammonia, which causes the appearance of a specific odor from the mouth.
Glands of the digestive tract(including the salivary glands) play a leading role in the secretion of excess calcium, bilirubin, bile acids, cholesterol and its derivatives. They can release heavy metal salts, drugs (morphine, quinine, salicylates), foreign organic compounds (for example, dyes), small amounts of water (100-200 ml), urea and uric acid. Their excretory function increases when the body is overloaded with an excessive amount of various substances, as well as in kidney diseases. At the same time, the excretion of protein metabolic products with the secretions of the digestive glands increases significantly.
Leather has a leading role in the processes of heat transfer by the body to the environment. The skin has special excretory organs - sweat and sebaceous glands. Sweat glands play an important role in the release of water, especially in hot climates and (or) intense physical work, including in hot shops. The release of water from the surface of the skin ranges from 0.5 l/day at rest to 10 l/day on hot days. Sodium, potassium, calcium salts, urea (5-10% of the total amount excreted from the body), uric acid, and about 2% carbon dioxide are also released with sweat. Sebaceous glands secrete a special fatty substance - sebum, which performs a protective function. It consists of 2/3 water and 1/3 unsaponifiable compounds - cholesterol, squalene, metabolic products of sex hormones, corticosteroids, etc.
Functions of the excretory system
Excretion is the liberation of the body from metabolic end products, foreign substances, harmful products, toxins, and medicinal substances. As a result of metabolism in the body, end products are formed that cannot be further used by the body and therefore must be removed from it. Some of these products are toxic to the excretory organs, so mechanisms are formed in the body aimed at converting these harmful substances either into harmless or less harmful to the body. For example, ammonia, formed during protein metabolism, has a harmful effect on renal epithelial cells, so in the liver ammonia is converted into urea, which does not have a harmful effect on the kidneys. In addition, the liver neutralizes toxic substances such as phenol, indole and skatole. These substances combine with sulfuric and glucuronic acids, forming less toxic substances. Thus, the processes of excretion are preceded by the processes of so-called protective synthesis, i.e. converting harmful substances into harmless ones.
Excretory organs include: kidneys, lungs, gastrointestinal tract, sweat glands. All these organs perform the following important functions: removal of metabolic products; participation in maintaining the constancy of the internal environment of the body.
Participation of excretory organs in maintaining water-salt balance
Functions of water: water creates an environment in which all metabolic processes take place; is part of the structure of all body cells (bound water).
The human body consists of 65-70% water. In particular, a person with an average weight of 70 kg has about 45 liters of water in the body. Of this amount, 32 liters is intracellular water, which is involved in building the structure of cells, and 13 liters is extracellular water, of which 4.5 liters is blood and 8.5 liters is intercellular fluid. The human body constantly loses water. About 1.5 liters of water are excreted through the kidneys, which dilutes toxic substances, reducing their toxic effect. About 0.5 liters of water per day are lost through sweat. The exhaled air is saturated with water vapor and 0.35 liters are removed in this form. About 0.15 liters of water are removed with the final products of food digestion. Thus, about 2.5 liters of water are removed from the body during the day. To maintain water balance, the same amount must enter the body: about 2 liters of water enter the body with food and drink, and 0.5 liters of water are formed in the body as a result of metabolism (exchange water), i.e. the water flow is 2.5 liters.
Regulation of water balance. Autoregulation
This process starts with a deviation in the water content constant in the body. The amount of water in the body is a rigid constant, since with insufficient water supply a shift in pH and osmotic pressure occurs very quickly, which leads to a profound disruption of the metabolism in the cell. A subjective feeling of thirst signals an imbalance in the body's water balance. It occurs when there is insufficient intake of water into the body or when it is released excessively (increased sweating, dyspepsia, when there is an excess intake of mineral salts, i.e., with an increase in osmotic pressure).
In various parts of the vascular bed, especially in the hypothalamus (in the supraoptic nucleus), there are specific cells - osmoreceptors containing a vacuole (vesicle) filled with liquid. These cells are surrounded by a capillary vessel. When the osmotic pressure of the blood increases, due to the difference in osmotic pressure, fluid from the vacuole will leak into the blood. The release of water from the vacuole leads to its shrinkage, which causes excitation of osmoreceptor cells. In addition, there is a feeling of dryness in the mucous membrane of the mouth and pharynx, while the receptors of the mucous membrane are irritated, impulses from which also enter the hypothalamus and increase the excitation of a group of nuclei called the thirst center. Nerve impulses from them enter the cerebral cortex and a subjective feeling of thirst is formed there.
With an increase in blood osmotic pressure, reactions begin to form that are aimed at restoring the constant. Initially, reserve water from all water depots is used, it begins to pass into the blood, in addition, irritation of the osmoreceptors of the hypothalamus stimulates the release of ADH. It is synthesized in the hypothalamus and deposited in the posterior lobe of the pituitary gland. The release of this hormone leads to a decrease in diuresis by increasing the reabsorption of water in the kidneys (especially in the collecting ducts). Thus, the body is freed from excess salts with minimal water loss. Based on the subjective sensation of thirst (thirst motivation), behavioral reactions are formed aimed at searching for and receiving water, which leads to a rapid return of the osmotic pressure constant to a normal level. This is how the process of regulating a rigid constant is carried out.
Water saturation occurs in two phases:
- phase of sensory saturation, occurs when water irritates the receptors of the mucous membrane of the oral cavity and pharynx, deposited water is released into the blood;
- the phase of true or metabolic saturation occurs as a result of the absorption of ingested water in the small intestine and its entry into the blood.
Excretory function of various organs and systems
The excretory function of the digestive tract is not only limited to removing undigested food debris. For example, in patients with nephritis, nitrogenous wastes are removed. When tissue respiration is impaired, underoxidized products of complex organic substances also appear in saliva. In case of poisoning in patients with symptoms of uremia, hypersalivation (increased salivation) is observed, which to a certain extent can be considered as an additional excretory mechanism.
Some dyes (methylene blue or congorot) are released through the gastric mucosa, which is used to diagnose gastric diseases during simultaneous gastroscopy. In addition, salts of heavy metals and medicinal substances are removed through the gastric mucosa.
The pancreas and intestinal glands also excrete heavy metal salts, purines and drugs.
Excretory function of the lungs
With exhaled air, the lungs remove carbon dioxide and water. In addition, most aromatic esters are removed through the alveoli of the lungs. Fusel oils are also removed through the lungs (intoxication).
Excretory function of the skin
During normal functioning, the sebaceous glands secrete metabolic end products. The secretion of the sebaceous glands serves to lubricate the skin with fat. The excretory function of the mammary glands manifests itself during lactation. Therefore, when toxic and medicinal substances and essential oils enter the mother’s body, they are released into the milk and can have an effect on the child’s body.
The actual excretory organs of the skin are the sweat glands, which remove waste products of metabolism and thereby participate in maintaining many constants of the internal environment of the body. With sweat, water, salts, lactic and uric acids, urea, and creatinine are removed from the body. Normally, the share of sweat glands in removing the products of protein metabolism is small, but in kidney diseases, especially acute renal failure, the sweat glands significantly increase the volume of excreted products as a result of increased sweating (up to 2 liters or more) and a significant increase in the urea content in sweat. Sometimes so much urea is removed that it is deposited in the form of crystals on the patient’s body and underwear. Sweat can remove toxins and drugs. For some substances, the sweat glands are the only organ of excretion (for example, arsenous acid, mercury). These substances, released through sweat, accumulate in the hair follicles and integument, which makes it possible to determine the presence of these substances in the body even many years after its death.
Excretory function of the kidneys
The kidneys are the main excretory organs. They play a leading role in maintaining a constant internal environment (homeostasis).
The functions of the kidneys are very extensive and involve:
- in regulating the volume of blood and other fluids that make up the internal environment of the body;
- regulate constant osmotic pressure of blood and other body fluids;
- regulate the ionic composition of the internal environment;
- regulate acid-base balance;
- provide regulation of the release of end products of nitrogen metabolism;
- provide excretion of excess organic substances supplied with food and formed during metabolism (for example, glucose or amino acids);
- regulate metabolism (metabolism of proteins, fats and carbohydrates);
- participate in the regulation of blood pressure;
- participate in the regulation of erythropoiesis;
- participate in the regulation of blood clotting;
- participate in the secretion of enzymes and physiologically active substances: renin, bradykinin, prostaglandins, vitamin D.
The structural and functional unit of the kidney is the nephron, in which the process of urine formation occurs. Each kidney has about 1 million nephrons.
The formation of final urine is the result of three main processes occurring in the nephron: and secretion.
Glomerular filtration
Urine formation in the kidneys begins with the filtration of blood plasma in the glomeruli. There are three barriers to the filtration of water and low molecular weight compounds: the endothelium of the glomerular capillaries; basement membrane; inner layer of the glomerular capsule.
At normal blood flow rates, large protein molecules form a barrier layer on the surface of the endothelial pores, preventing the passage of formed elements and fine proteins through them. Low molecular weight components of blood plasma could freely reach the basement membrane, which is one of the most important components of the glomerular filtering membrane. Pores in the basement membrane restrict the passage of molecules based on their size, shape, and charge. The negatively charged pore wall makes it difficult for molecules with the same charge to pass through and limits the passage of molecules larger than 4-5 nm. The last barrier to the filtered substances is the inner layer of the glomerular capsule, which is formed by epithelial cells - podocytes. Podocytes have processes (feet) with which they attach to the basement membrane. The space between the legs is blocked by slit membranes, which limit the passage of albumin and other molecules with a large molecular weight. Thus, such a multilayer filter ensures the preservation of formed elements and proteins in the blood, and the formation of a practically protein-free ultrafiltrate - primary urine.
The main force providing filtration in the renal glomeruli is the hydrostatic pressure of the blood in the capillaries of the glomerulus. The effective filtration pressure, on which the glomerular filtration rate depends, is determined by the difference between the hydrostatic blood pressure in the capillaries of the glomerulus (70 mm Hg) and the factors counteracting it - the oncotic pressure of plasma proteins (30 mm Hg) and the hydrostatic pressure of the ultrafiltrate in glomerular capsule (20 mm Hg). Therefore, the effective filtration pressure is 20 mmHg. Art. (70 - 30 - 20 = 20).
The amount of filtration is influenced by various intrarenal and extrarenal factors.
Renal factors include: the magnitude of hydrostatic blood pressure in the capillaries of the glomerulus; number of functioning glomeruli; the pressure value of the ultrafiltrate in the glomerular capsule; degree of permeability of glomerular capillaries.
Extrarenal factors include: blood pressure in the great vessels (aorta, renal artery); renal blood flow velocity; the value of oncotic blood pressure; functional state of other excretory organs; degree of tissue hydration (amount of water).
Tubular reabsorption
Reabsorption is the reabsorption of water and substances necessary for the body from primary urine into the blood. In the human kidneys, 150-180 liters of filtrate or primary urine are formed per day. About 1.5 liters of final or secondary urine are excreted, the rest of the liquid part (i.e. 178.5 liters) is absorbed in the tubules and collecting ducts. Reabsorption of various substances is carried out due to active and passive transport. If a substance is reabsorbed against a concentration and electrochemical gradient (i.e., with the expenditure of energy), then this process is called active transport. There are primary active and secondary active transport. Primary active transport is the transfer of substances against an electrochemical gradient and is carried out using the energy of cellular metabolism. Example: the transfer of sodium ions, which occurs with the participation of the enzyme sodium-potassium ATPase, which uses the energy of adenosine triphosphate. Secondary active transport is the transfer of substances against a concentration gradient, but without the expenditure of cell energy. Using this mechanism, glucose and amino acids are reabsorbed.
Passive transport occurs without energy consumption and is characterized by the fact that the transfer of substances occurs along an electrochemical, concentration and osmotic gradient. Due to passive transport, the following are reabsorbed: water, carbon dioxide, urea, chlorides.
The reabsorption of substances in different parts of the nephron is not the same. In the proximal segment of the nephron, glucose, amino acids, vitamins, trace elements, sodium and chlorine are reabsorbed from the ultrafiltrate under normal conditions. In subsequent sections of the nephron, only ions and water are reabsorbed.
The functioning of the rotary-countercurrent system is of great importance in the reabsorption of water and sodium ions, as well as in the mechanisms of urine concentration. The nephron loop has two branches - descending and ascending. The epithelium of the ascending knee has the ability to actively transfer sodium ions into the intercellular fluid, but the wall of this section is impermeable to water. The epithelium of the descending limb allows water to pass through, but does not have mechanisms for transporting sodium ions. Passing through the descending part of the nephron loop and releasing water, primary urine becomes more concentrated. Reabsorption of water occurs passively due to the fact that in the ascending section there is an active reabsorption of sodium ions, which, entering the intercellular fluid, increase the osmotic pressure in it and promote the reabsorption of water from the descending sections.
The excretory system is a set of organs that remove excess water, end products of metabolism (carbon dioxide, urea, uric acid, etc.), as well as salts and foreign substances from the body of animals and humans. Excretion processes play an important role in the body, maintaining the constancy of the chemical composition and volume of fluids in the internal environment, osmotic pressure is a necessary condition for the effective functioning of various organs and systems (see Homeostasis).
In protozoa, excretory products are eliminated by diffusion or with the help of contractile vacuoles. In multicellular aquatic invertebrates, excretion is carried out by special excretory organs - protonephridia and metanephridia (in worms), coelomoducts (in mollusks) or special glands (in crustaceans). In terrestrial inhabitants (mainly insects and arachnids), excretory functions are performed by the intestinal walls, and more often by the so-called Malpighian vessels, the physiological advantage of which is that precipitated metabolic products (uric acid, etc.) are excreted in the urine into the hindgut, where water is absorbed, and dehydrated waste products, along with undigested food debris, are expelled through the anus. The excretory system of invertebrates is shown in Fig. 12.
Excretory functions in vertebrates are performed by the kidneys, lungs, liver, colon, and skin. The lungs remove carbon dioxide and water from the body, the liver - bile pigments (products of the breakdown of hemoglobin), the colon - calcium salts and heavy metals, the skin - water, urea, sodium salts, etc. However, the main organ of excretion is the kidneys (Fig. 4) , removing water, urea, uric acid, creatine, salts.
The excretory system of vertebrates has two sections: the urinary (kidneys) and the urinary excretory, consisting of the ureters, bladder and urethra (Fig. 3).
The structural and functional urinary elements of the kidneys of vertebrates are the renal corpuscles, or nephrons (Fig. 5). The nephron capsule contains a glomerulus of approximately 50 capillary loops. Moreover, the vessel that brings blood is almost twice as wide as the vessel that carries it out. Blood pressure in the afferent arteriole is 95, in the capillary glomerulus - 57, and in the efferent vessel - 25 mm Hg. Art. Due to this, blood is filtered through the membranes of the cells of the capillary glomerulus and capsule. This is how primary urine appears, containing both newly used (sugars, simple proteins, etc.) and waste products excreted from the body.
In convoluted tubules, intertwined with a network of capillaries, some of the water with nutrients is absorbed and secondary urine is formed, in which the amount of substances unnecessary for the body increases sharply. Through straight tubules, urine flows into the cavity of the kidneys and then into the ureters - paired tubes ending in sphincters. Urine flows through them into the unpaired bladder. Its smooth muscles lie in three layers. When the bladder fills, its sphincter reflexively opens, and urine is removed from the body.
The functional activity of the kidneys is high. Their mass in humans is only 120-200 g, and during the day about 700 liters of blood flows through them at rest, and up to 1500 liters or more during intense work. On average, about 17 liters of primary and 1.5 liters of secondary urine are formed per day.
The kidneys are an autonomously working organ, the rate of urine formation in which is regulated by both nervous and humoral influences. Impulses from the chemical receptors of the aortic arch, renal pelvis, bladder, rectum through the urinary centers of the spinal and diencephalon cause a change in blood flow to the nephrons, opening or closing the sphincters of the afferent vessels. Urination (diuresis) changes depending on the quantity and quality of food eaten and drunk, temperature, time of year, etc.
In adolescents, by the age of 13-15 years, the kidneys reach the structural and functional parameters of adults.
❖ The need for excretory processes in the body:
■ some of the substances formed during metabolism from food are not used by the body ( end products of metabolism), and their accumulation in the internal environment of the body would lead to its poisoning;
■ it is necessary to remove toxic foreign substances from the body that have entered it ( xenobiotics) - nicotine, alcohol, many medications, poisons, etc.
♦Organs that provide excretory processes in humans:
■ urinary system (plays a major role in excretory processes) removes liquid metabolic products and xenobiotics from the body;
■ sweat glands remove water and mineral solutions from the body;
■ lungs release gaseous metabolic products into the atmosphere - carbon dioxide and water vapor, as well as alcohol vapor during intoxication, ether vapor after anesthesia, etc.;
Organs of the urinary system
Composition of the urinary system: two kidneys, two ureters, bladder, urethra.
Kidneys human - paired organs located in the back of the abdominal cavity at the lumbar level on both sides of the spine.
Ureter- the excretory duct of the kidney, connecting the renal pelvis with the bladder and representing a hollow tube, the wall of which is formed by smooth muscles. Through the ureter, urine from the kidney continuously flows into the bladder, and the movement of urine occurs as a result of wave-like propagating (peristaltic) muscle contractions.
Bladder is a hollow muscular organ in which urine is heated (up to 800 ml) before periodically removing it from the body. The wall of the bladder consists of smooth muscle cells; When the bladder fills with urine, it stretches and thins. The outlet from the bladder into the urethra is blocked by a valve - sphincter .
Urethra (urethra)- a muscular tube extending from the bladder through which urine is removed outside the body.
Sphincter- a circular muscle, the contraction of which prevents urine from flowing out of the bladder.
Structure and Function of the Kidneys
The structure of the kidneys. Each bud is shaped like a bean, about 10 cm long, with its concave side facing the lower back. It consists of an outer dark layer formed cortex , inner light medulla and is covered with a capsule, to which a layer of fatty tissue is adjacent to the outside. Located at the upper pole of the kidney adrenal (endocrine gland). The cortical substance in the form of columns enters the medulla and divides it into 15-20 renal pyramids, the tops of which are directed inside the kidney. From the top of each of the medulla pyramids, a urinary canaliculus extends into a small cavity inside the kidney - renal pelvis, in which urine collects. On the concave side of the kidney, a deep notch adjoins the renal pelvis - hilum of the kidney, through which it enters the kidney renal artery and go out renal vein And ureter (the ureter originates in the renal pelvis).
Through the renal artery, unpurified blood enters the kidney; through the renal vein, blood purified from liquid decay products from the kidney enters the bloodstream system; through the ureter, removed substances in the form of urine enter the bladder.
Structural and functional unit of the kidney, which carries out the entire set of processes of urine formation, is iephron . One human kidney contains about a million nephrons.
Nephron consists of a small renal corpuscle
(located in the cortex) and ^ branched system tubules
. The renal corpuscle is formed capsule
in the form of a double-walled bowl, inside of which there is a tangle of blood capillaries ( malpighian glomerulus
). Between the walls of the capsule there is a cavity from which a long convoluted first order nephron tubule
, passing through the renal cortex into the medulla. The wall of the tubule consists of a single layer of squamous epithelial cells. 
At the border of the cortex, this tubule straightens, narrows and penetrates deeply into the medulla. Then, turning 180°, it follows in the opposite direction, forming loop of Henle. After this, the tubule reenters the cortex, where it expands and acquires bends, turning into second-order canaliculus , and flows into collecting duct . The total length of the tubules of one nephron is 50-55 mm, and the total filtering surface of one kidney is up to 3 m2.
collecting duct(or collecting duct) is a canal into which the second-order tubules of several dozen nephrons flow. The collecting ducts go to the renal pelvis.
Blood flow in the kidney. Renal artery , entering the gate of the kidney, branches into small arterioles. Each of the arterioles enters one of the capsules, where it forms a capillary glomerulus consisting of approximately 50 primary capillaries . Then these capillaries unite, passing into the efferent arteriole, which leaves the capsule and again branches into secondary capillaries , densely entwining the convoluted tubules of the first order, the loop of Henle and the tubules of the second order. From the capillaries, blood enters small venules, which merge into the renal vein , flowing into the inferior vena cava. The blood flow through each kidney is about 0.6 liters (10-12% of the total blood volume) per minute.
Kidney weight person is about 150 g.
❖ Kidney functions:
■ filtering: removal from the body of excess water and mineral salts, as well as metabolic products (urea, uric acid, etc.), foreign and toxic substances formed in the body or taken in the form of medications, when smoking, etc.;
■ homeostatic: participation in the processes of regulation of the acid-base reaction of the blood (with an increase in the concentration of acidic or alkaline metabolic products in the blood, the rate of removal of the corresponding salts from the body through the kidneys increases), the constancy of the ionic composition of the blood (occurs with the participation of ammonia, which replaces sodium ions Na in acidic metabolic products + and potassium K + , preserving them for the needs of the body), constancy of the volume of blood, lymph and tissue fluid in the body (volume regulation) as well as osmotic pressure of the blood (osmoregulation);
■ synthesizing: synthesis and release into the blood of some biologically active substances (enzyme renina , involved in biochemical reactions of the breakdown of plasma proteins, as well as hormones erythropoietin stimulating hematopoiesis, angiotensin and etc.); in the kidneys, inactive vitamin D 3 is converted into a physiologically active form;
■ regulatory: participation in regulation blood pressure (here the mediator is renin, with the participation of which hormones are formed from certain plasma proteins in the kidneys angiotensins , increasing blood pressure);
■ metabolic: kidney tissue can synthesize glucose (a process gluconeogenesis ); During prolonged fasting, about half of the glucose produced in the body is synthesized in the kidneys.
Urine, its composition and formation
Urine- a liquid excretory product formed in the kidneys and removed from the body; is a transparent, yellowish solution of substances filtered from the blood; contains on average 98% water, 1.5% salts (mainly NaCl), about 2.5% organic substances (mainly urea and uric acid), as well as bilirubin (a breakdown product of hemoglobin excreted by the liver) and foreign substances.
■ The composition of urine depends on the condition of the body.
■ The volume of urine excreted per day can vary widely and depends on the condition of the body; in a healthy adult it is about 1.5 liters.
■ The yellowish color of urine is due to the color of hemoglobin breakdown products.
■ After eating a meal rich in carbohydrates and doing heavy physical work, a small amount of glucose that is not normally present may appear in the urine.
■ When you have diabetes, glucose is constantly present in the urine.
■ In cases of kidney disease, protein is found in the urine.
Urea(formula O=C(NH 2) 2) - the final product of protein metabolism; formed (approximately 25-30 g per day) from carbon dioxide and ammonia in the liver; excreted in urine and sweat.
Uric acid- one of the breakdown products of purines, which are components of nucleic acids. It is excreted from the body in urine and excrement.
■ With gout, uric acid and its acid salts are deposited in joints and muscles; in some metabolic disorders they can form stones in the kidneys and bladder.
Urine formation. The process of urine formation is divided into two stages: in the first stage, it is formed from blood plasma primary urine , at the second stage - secondary (cm. " ").
The first stage is glomerular filtration . The diameter of the afferent arteriole of the Malpighian glomerulus is twice the diameter of the efferent arteriole, so the exit of blood from the glomerulus is difficult, and a higher (2-3 times) blood pressure is created in its capillaries than in other capillaries of the body. Under the influence of high pressure, blood plasma passes from the capillaries of the glomerulus into the cavity of the adjacent nephron tubule, while the thin walls of the capillaries of the glomerulus and the nephron capsule act as filters, passing the plasma and small molecules of low molecular weight compounds dissolved in it (glucose, amino acids, vitamins, etc.), but retaining blood cells and large protein molecules.
The resulting filtrate, consisting of blood plasma devoid of proteins, is primary urine; About 150-160 liters of it are formed every day.
The second stage is tubular reabsorption (or reabsorption) . At this stage, from the primary urine moving along the tortuous tubule of the nephron, substances necessary for the body (glucose, amino acids, vitamins, sodium and calcium ions, etc.) and most (99%) of water are absorbed back into the blood of the capillaries that entwin a dense network of tubules. . As a result, a small amount of water remains in the tubule, saturated with end products of metabolism and substances that are unnecessary for the body or those that it is not able to store (for example, glucose in diabetes mellitus).
Reabsorption requires large amounts of energy: kidney energy consumption accounts for approximately 9% of total body energy consumption, while kidney mass accounts for only 4% of body weight.
Tubular reabsorption is accompanied by tubular synthesis (formation of nitrogen-hydrogen ions from ammonia molecules retained by urine) and selective tubular secretion — release into the lumen of the nephron tubule of xenobiotics, potassium ions, protons, etc. (occurs due to active transport;).
As a result of the processes of tubular reabsorption, secretion and synthesis from primary urine, secondary urine ; About 1.5 liters of it are produced every day.
The final secondary urine formed in the nephron tubule flows through the collecting duct into the renal pelvis, and from there through the ureter into the bladder.
Regulation of kidney activity
Mechanisms for regulating the functional activity of the kidneys:
■ neuro-reflex: excitation of certain centers of the sympathetic department of the autonomic nervous system leads to a narrowing of the lumen of the renal arterioles - afferent (then the influx and pressure of blood in the Malpighian glomerulus decreases, plasma filtration slows down and, as a result, the formation of primary urine decreases) or efferent (then the blood pressure in the glomerulus increases, plasma filtration increases and primary urine formation increases);
■ humoral: the intensity of all processes of urine formation (filtration, reabsorption, tubular synthesis and secretion) changes under the influence of hormones pituitary gland (vasopressin enhances the reabsorption of water from the tubules and at the same time weakens the reabsorption of Na + and C1 - ions, as a result of which the volume of urine formation decreases), adrenal glands (adrenaline reduces urination, aldosterone enhances the reabsorption of Na + ions), themselves kidney (angiotensin II narrows the lumens of the efferent arterioles of the glomeruli, increasing filtration), thyroid and parathyroid glands (their hormones indirectly affect urine formation by changing water-mineral metabolism in tissues) and other glands; in this case, the amount of urine produced may decrease or increase, but the content of urea and uric acid in it will remain unchanged.
The interaction of the neuro-reflex and humoral mechanisms ensures the water-mineral homeostasis of the body by regulating the composition and amount of urine excreted.
Urination
Urination- a reflex process consisting of simultaneous contraction of the bladder and relaxation of the sphincters of the bladder and urethra, leading to the removal of urine from the bladder.
Involuntary urination(typical for children under 2-3 years of age). The walls of the bladder contain receptors that respond to the stretching of smooth muscle tissue. When urine accumulates in the bladder, its walls stretch, irritating the receptors. Excitation from these receptors is transmitted along the afferent nerves of the reflex arc to the micturition center located in the sacral segments of the spinal cord. From here, impulses along the axons of the efferent nerves of the reflex arc enter the muscles of the bladder and the sphincters of the bladder and urethra, causing the muscles of the walls to contract and the sphincters to relax. As a result, urine enters the urethra and is removed from the body.
Enuresis- bedwetting; usually observed in 5-10% of children under the age of 13-14 years. With this disease, you need to exclude salty and spicy foods from your diet, and do not drink a lot of liquid at night; special treatment is required.
Voluntary (conscious) regulation of urination It is established when the size of the bladder increases (as a result of the child’s growth) and under the influence of the environmental environment (parents, friends). It is possible due to the existence of connections between the neurons of the cerebral cortex and the nerve cells of the sacral spinal cord, allowing the higher parts of the human central nervous system - the cerebral hemispheres - to control the spinal urination center and consciously control the act of urination.
■ In children, voluntary urination develops by the age of 2-3 years.
Hygiene of the urinary system
❖ Inflammatory processes caused by microorganisms:
■pathogenic microorganisms can penetrate the organs of the urinary system through the blood ( descending infections ); this is how infectious diseases of the urinary system arise, provoked by sore throat, caries, diseases of the oral cavity, etc.;
■ germs can enter the urethra, from where they spread through the urinary tract to other organs of this system ( ascending infections ); This path of disease occurrence is facilitated by non-compliance with personal hygiene rules, cooling the body, and colds.
Inflammation The urethra and urinary tract are characterized by intensive desquamation of the epithelium and its high vulnerability.
Nephritis- inflammation of the kidneys, leading to disruption of their function; characterized by increased temperature, impaired protein-fat metabolism, edema, and the release of blood in the urine.
■ With nephritis, the permeability of the walls of the capillaries of the kidneys increases, so proteins and blood cells are found in the urine, edema occurs (filling of tissues with fluid), and possible poisoning of the body with metabolic products - uremia .
Kidney dysfunction and disease due to their sensitivity to toxic substances:
■ impaired kidney function can be caused by lead, mercury, boric acid, naphthalene, benzene, insect and snake poisons, etc., entering the blood;
■ Alcohol abuse is especially harmful, as it damages the kidneys;
■ kidney diseases can be caused by certain medications (sulfonamides, antibiotics) if they are overdosed.
❖Formation of "stones" in the kidneys and urinary tract is associated with metabolic disorders:
■ stones are formed by urates (uric acid salts) or calcium phosphates;
■ they disrupt the outflow of urine, and with their sharp edges they irritate the mucous membrane, causing severe pain.
♦Basic rules of personal hygiene and prevention of diseases of the urinary organs:
■ it is necessary to keep the external genitalia clean, wash them with warm water and soap in the morning and evening before bed;
■ avoid hypothermia of the kidneys;
■ do not abuse alcohol and spicy foods containing excess spices and salt;
■ follow safety rules when working with toxic substances;
■ avoid overdosing on medications.
The vital activity of our body is ensured by the coordinated functioning of our organ systems.
An important role in the regulation and performance of all functions is played by the human excretory organs.
Nature has awarded us with special organs that help remove metabolic products from the body.
What excretory organs does a person have?
The human organ system consists of:
- kidney,
- Bladder,
- ureters,
- urethra.
In this article we will take a detailed look at the human excretory organs and their structure and functions.
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-shaped and inside – parenchymal structure. Length one kidney no more than 12 cm, and width– from 5 to 6 cm. Normal weight kidneys do not exceed 150-200 g.
Structure
The membrane that covers the outside of the kidney is called fibrous capsule. On a sagittal section, two different layers of substance can be seen. The one located closer to the surface is called cortical, and the substance occupying the central position is cerebral.
They have not only external differences, but also functional ones. On the side of the concave part there are hilum of the kidney and pelvis, and ureter.
Through the renal hilum, the kidney communicates with the rest of the body through the incoming renal artery and nerves, as well as the outgoing lymphatic vessels, the renal vein and the ureter.
The collection of these vessels is called renal pedicle. Inside the kidney there are renal lobes. There are 5 pieces in each kidney. The renal lobes are separated from each other by blood vessels.
In order to clearly understand the functions of the kidneys, it is necessary to know them. microscopic structure.
The main structural and functional unit of the kidneys is nephron.
Number of nephrons in the kidney reaches 1 million. The nephron consists of renal corpuscle, which is located in the cortex, and tubule systems, which ultimately flow into the collecting duct.
In the nephron there are also 3 segments:
- proximal,
- intermediate,
- distal.
Segments along with the ascending and descending limbs of the loop of Henle lie in the renal medulla.
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 body;
- blood formation, by producing erythrogenin;
- synthesis of such hormones, such as renin, erythropoietin, prostaglandin.
Bladder
The organ that stores urine that passes through the ureters and removes it 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 there are
- top,
- body,
- neck
The latter narrows, thus passing into the urethra. When filled, the walls of the organ stretch, signaling the need to empty.
When the bladder is empty, its walls thicken, and the mucous membrane gathers into folds. But there is a place that remains unwrinkled - this is the triangular area between the opening of the ureter and the opening of the urethra.
Functions
The bladder performs the functions:
- temporary accumulation of urine;
- urine excretion– the volume of urine accumulated by the bladder is 200-400 ml. Every 30 seconds, urine flows into the bladder, but the time of entry depends on the amount of liquid drunk, temperature, and so on;
- thanks to mechanoreceptors that are located in the wall of the organ, it is carried out control of the amount of urine in the bladder. Their irritation serves as a signal to contract the bladder and remove urine out.
Ureters
The ureters are thin ducts that connects the kidney and bladder. Their length is no more than 30 cm, and diameter from 4 to 7 mm. 
Structure
The tube wall 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 difficulties in the outflow of urine (stones), the ureter may expand in some area up to 8 cm.
Functions
The main function of the ureter is urine outflow accumulated in the bladder. Due to contractions of the muscle membrane, urine moves through the ureter into the bladder.
Urethra
In women and men, the urethra differs in its structure. This is due to the difference in genital organs.
Structure
The canal itself consists of 3 membranes, like the ureter. Because women have a urethra 
In short, than in men, women are more often exposed to various diseases and inflammations of the urogenital tract.
Functions
- In men the channel performs several functions: excretion of urine and sperm. The fact is that the vas deferens ends in the canal tube, through which sperm flows through the canal into the head of the penis.
- Among women The urethra is a tube 4 cm long and performs only the function of excreting urine.
How are primary and secondary urine formed?
The process of urine formation includes three interconnected stages:
- glomerular filtration,
- tubular reabsorption,
- tubular secretion.
First stage - 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 allow dissimilation products and amino acids to pass through, and also prevent the passage of most proteins.
During glomerular filtration, it is formed ultrafiltrate, representing primary urine. It is similar to blood plasma, but contains few proteins.
During the day, a person produces from 150 to 170 liters of primary urine, but only 1.5-2 liters turns into secondary urine, which is excreted from the body.
The remaining 99% returns to the blood.
Mechanism formation of secondary urine consists in the passage of ultrafiltrate through 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 is a set of processes due to which substances to be excreted from the body are secreted into the lumen of the nephron tubules. That is, this secretion is nothing more than a reserve process of urine formation.
Elimination is the removal of toxins produced by metabolism from the body. This process is a necessary condition for maintaining the constancy of its internal environment - homeostasis. The names of animal excretory organs are varied - specialized tubes, metanephridia. A person has a whole mechanism to carry out this process.
Excretory organ system
Metabolic processes are quite complex and occur at all levels - from molecular to organismal. Therefore, a whole system is needed to implement them. The human excretory organs remove various substances.
Excess water is removed from the body through the lungs, skin, intestines and kidneys. Heavy metal salts are released by the liver and intestines.
The lungs are respiratory organs, the essence of which is the entry of oxygen into the body and the removal of carbon dioxide from it. This process has global significance. After all, plants use carbon dioxide released by animals for photosynthesis. In the presence of water and light in the green parts of the plant, which contain the pigment chlorophyll, they form the carbohydrate glucose and oxygen. This is the cycle of substances in nature. Excess water is also continuously removed through the lungs.
The intestines remove undigested food debris, and along with them harmful metabolic products that can cause poisoning of the body.
The digestive gland, the liver, is a real filter for the human body. It removes toxic substances from the blood. The liver secretes a special enzyme - bile, which disarms toxins and removes them from the body, including the poisons of alcohol, drugs and medications.
The role of the skin in excretion processes
All excretory organs are irreplaceable. Indeed, if their functioning is disrupted, toxic substances - toxins - will accumulate in the body. The largest human organ, the skin, plays a special role in this process. One of its most important functions is thermoregulation. During intense work, the body generates a lot of heat. As it accumulates, it can cause overheating.
The skin regulates the intensity of heat transfer, retaining only the required amount. Along with sweat, in addition to water, mineral salts, urea and ammonia are removed from the body.
How does heat transfer occur?
Man is a warm-blooded creature. This means that his body temperature does not depend on the climatic conditions in which he lives or is temporarily located. Organic substances that come with food: proteins, fats, carbohydrates are broken down into their components in the digestive tract. They are called monomers. During this process, a large amount of thermal energy is released. Since the ambient temperature is most often lower than body temperature (36.6 degrees), according to the laws of physics, the body releases excess heat to the environment, i.e. in the direction where there is less of it. This maintains temperature equilibrium. The process of heat release and production by the body is called thermoregulation.
When does a person sweat the most? When it's hot outside. And in the cold season, practically no sweat is released. This happens because it is not beneficial for the body to lose heat when there is not very much of it anyway.
The process of thermoregulation is also influenced by the nervous system. For example, when your palms sweat during an exam, this means that in a state of excitement the blood vessels dilate and heat transfer increases.
Structure of the urinary system
The urinary system plays an important role in the processes of excretion of metabolic products. It consists of paired kidneys, ureters, and a bladder, which opens to the outside through the urethra. The figure below (diagram "Organs of excretion") illustrates the location of these organs.
The kidneys are the main excretory organ
The human excretory organs begin as paired bean-shaped organs. They are located in the abdominal cavity on both sides of the spine, towards which they are turned with the concave side.
On the outside, each of them is covered with a shell. Through a special depression called the renal hilum, blood vessels, nerve fibers and ureters enter the organ.
The inner layer is formed by two types of substances: cortical (dark) and medulla (light). Urine is formed in the kidney, which is collected in a special container - the pelvis, flowing from it into the ureter.
Nephron is the basic unit of the kidney.
In particular, the kidney consists of elementary structural units. It is in them that metabolic processes occur at the cellular level. Each kidney consists of a million nephrons - structural and functional units.
Each of them is formed by a renal corpuscle, which, in turn, is surrounded by a goblet-shaped capsule with a tangle of blood vessels. Urine initially collects here. From each capsule extend convoluted tubules of the first and second tubules, opening into collecting ducts.
Mechanism of urine formation
Urine is formed from blood through two processes: filtration and reabsorption. The first of these processes occurs in the nephron bodies. As a result of filtration, all components except proteins are released from the blood plasma. Thus, there should not be this substance in the urine. And its presence indicates a violation of metabolic processes. As a result of filtration, a liquid is formed, which is called primary urine. Its quantity is 150 liters per day.
Then comes the next stage - reabsorption. Its essence lies in the fact that all substances useful to the body are absorbed back into the blood from primary urine: mineral salts, amino acids, glucose, and large amounts of water. As a result, secondary urine is formed - 1.5 liters per day. A healthy person should not have the monosaccharide glucose in this substance.
Secondary urine consists of 96% water. It also contains sodium, potassium and chlorine ions, urea and uric acid.
Reflex nature of urination
From each nephron, secondary urine enters the renal pelvis, from which it flows through the ureter into the bladder. It is a muscular unpaired organ. The volume of the bladder increases with age and in an adult reaches 0.75 liters. The bladder opens to the outside through the urethra. At the exit, it is limited by two sphincters - circular muscles.
For the urge to urinate to occur, about 0.3 liters of liquid must accumulate in the bladder. When this happens, the receptors in the walls are irritated. The muscles contract and the sphincters relax. Urination occurs voluntarily, i.e. an adult is able to control this process. Urination is regulated by the nervous system; its center is located in the sacral part of the spinal cord.
Functions of excretory organs
The kidneys play an important role in the process of removing end products of metabolism from the body, regulate water-salt metabolism and maintain the constancy of the fluid environment of the body.
The excretory organs cleanse the body of toxins, maintaining a stable level of substances necessary for the normal, full functioning of the human body.
