Organs involved in the release of end products of metabolism. Terminological dictations. System and functions of human excretory organs

"Anatomy of the excretory system"

The importance of excretion of metabolic end products from the body.

Excretion represents the last stage of the body's exchange with the external environment. During the process of life, proteins, fats and carbohydrates are broken down in tissues and energy is released. The final decomposition products are water, carbon dioxide, ammonia, urea, uric acid, phosphate salts and other compounds. These substances cannot undergo further transformations in the body. Their removal ensures the preservation of the constancy of the composition of the internal environment. Without food (in the presence of water), a person can live about 30 days, and when kidney activity stops, acute poisoning of the body occurs and the person dies within 4-5 days. Decay products from tissues pass into the blood, are carried by the blood to the excretory organs and through them are removed from the body. The release of these substances involves the lungs, skin, digestive tract and organs of the urinary system, through which most of the decay products are released. This system includes the kidneys, ureters, bladder and urethra.

The organs of the urinary system include the kidneys (organs whose excretion is urine) and the system that serves to accumulate and excrete urine - the ureters, bladder, and urethra.

Kidney, external and internal structure, function. The concept of nephron.

P The glasses are located on the sides of the spine, in the retroperitoneal space, at the level of the XI-XII thoracic and I-II lumbar vertebrae. Fixation of the kidney in this place is due to intra-abdominal pressure, the presence of renal fascia, renal arteries and veins, and a renal bed formed by the lumbar muscles. In the kidney, there are upper and lower poles, anterior and posterior surfaces, lateral and medial edges. In the area of ​​the medial edge there are the renal gates, which lead into the recess - the renal sinus. The portal enters the renal artery and nerves, and exits the renal vein, ureter and lymphatic vessels. The renal sinus contains the small and large renal calyces, the renal pelvis, from which the ureter originates, blood and lymph vessels, nerves, and adipose tissue. On a section in the kidney, the cortex and medulla can be distinguished. The cortex is located along the periphery of the organ and has a thickness of about 4 mm. The medulla of the kidney is composed of conical structures called renal pyramids. With their wide base they face the surface of the organ, and their apexes face the sinus. The apices are connected into rounded elevations - papillae, which open into small renal calyces. Urine formation occurs in the structural and functional unit of the kidney - nephron. The nephron consists of a glomerulus of capillaries placed in a double-walled capsule of the glomerulus (Shumlyansky-Bowman), convoluted tubules of the first order extending from the capsule of the glomerulus, loop of Henle located in the medulla, convoluted tubules of the second order lying in the cortex and the intercalary region. The length of one nephron is 35-50 mm. The total length of all tubules is 70-100 km, and their surface is 6 m2.

Nephron function. When blood passes through the capillaries of the Malpighian glomeruli, water and substances dissolved in it are filtered from the plasma through the capillary wall into the capsule cavity, with the exception of large molecular compounds and blood cells. Filtration is ensured by the difference in blood pressure in the capillaries and capsule. High blood pressure in the capillaries is created by the fact that the diameter of the afferent vessel is larger than that of the efferent vessel. In addition, the renal arteries arise directly from the abdominal aorta and pump blood under high pressure. The filtered liquid that enters the lumen of the capsule, which contains urea, uric acid, glucose, amino acids, and ions of inorganic substances, is called primary urine.

During the day, 1500-1800 liters of blood flow through the kidneys and 150-180 liters of primary urine are formed. From the glomerular capsule, primary urine enters the tubule, which is densely braided with secondarily branched blood capillaries. Here, most of the water and a number of substances are absorbed into the blood: glucose, amino acids, vitamins, sodium ions, potassium, calcium, chlorine. That part of the urine that remains at the end of its passage through the tubules is called secondary. It contains: urea, uric acid, ammonia, sulfates, phosphates, sodium, potassium, etc., i.e. Secondary urine contains no proteins or sugar. The concentration of substances in secondary urine is increased many times. The yellow color of urine is due to the pigment urobilin. Secondary urine is produced about 1.5 liters per day

The kidney performs a number of vital functions: it removes the end products of protein metabolism and salts; endogenous and exogenous toxic substances dissolved in water (without excretion, the body dies in 1–2 days); participates in the metabolism of carbohydrates and lipids; regulate mineral homeostasis, regulate the content of the number of red blood cells; regulate the volume of extracellular fluid and blood pressure.

Ureter, bladder, urethra.

M Ottoman. It connects the renal pelvis to the bladder. The ureter is a flattened tube about 30 cm long and 4 to 7 mm in diameter. The walls of the ureter consist of three membranes: mucous, muscular and connective tissue. There are several parts in the ureter: the abdominal part (from the kidney to the bend through the boundary line of the small pelvis), the pelvic part (along the pelvis) and the intramural part (in the wall of the bladder itself). There are several narrowings along the ureter: at the transition of the pelvis to the ureter, at the border between the abdominal and pelvic parts, along the pelvic part and at the entrance to the bladder.

Bladder. It is located in the pelvic cavity behind the pubic symphysis and is an organ in which urine coming from the ureter accumulates. The capacity of the bladder is 500-700 ml. The bladder consists of a fundus (directed downwards and backwards), an apex (directed forwards and upwards), a body (the middle part between the bottom and the apex) and a neck (the most narrowed part, directed downwards and passing into the urethra). The wall of the bladder consists of several layers: mucous membrane, submucosa, muscular and serous membranes. The peritoneum is only partially an integral part of the bladder wall and covers the empty bladder on one side (extraperitoneal) and the full bladder on three sides (mesoperitoneal). The muscular layer consists of three intertwined layers: outer - longitudinal, middle - circular and inner - longitudinal and circular. All three layers of muscle fibers form a common muscle, which is called the muscle that expels urine. The middle layer forms the bladder sphincter in the area of ​​the internal opening of the urethra.

Urethra. It has an S-shape with two bends (male). It has parts: prostatic, membranous, spongy. The female urethra runs in the form of a tube 3-3.5 cm long.

LEATHER

Structure and function of the skin. There are three layers in the skin. Epidermis (cuticle), the skin itself, or the dermis and subcutaneous tissue. The epidermis is a stratified squamous keratinizing epithelium, 0.07 - 2.5 mm or more thick. Its upper layers become keratinized and create a durable coating, especially on the palms and soles, where constant pressure and friction occur. As cells age, they slough off and are replaced by multiplying, deeper-lying cells at the base of the epidermis, which are cylindrical in shape with large nuclei. The layers of these cells make up the so-called germinal, or malpighian, layer. This layer contains pigment cells that synthesize skin pigment, which determine the color of the skin. The pigment protects against the harmful effects of ultraviolet rays. Therefore, when exposed to sunlight, the amount of pigment increases. This phenomenon is called tanning. The epidermis contains sensory nerve endings. They perceive touch, pressure, heat, cold.

The next layer is the skin itself. It contains the papillary and reticular layers. The papillary layer consists of loose connective tissue and forms papillae that protrude into the epidermis, which form a relief pattern of the skin from lines of different configurations. Their shape and location are strictly individual. The connective tissue of the papillary layer consists of collagen and elastic fibers, which provide strength and elasticity to the skin. This layer contains blood and lymphatic vessels, nerve fibers and their endings, which contain all kinds of receptors. Here are cells with pigment, muscle cells and their bundles. They are involved in raising hair and secreting secretions of the skin glands, maintaining skin tension. The papillary layer provides nutrition to the epidermis, which does not have blood capillaries. The blood vessels of the papillary layer act as a blood depot because they have a large total volume. The papillary layer passes inwards into the reticular layer, which consists of connective tissue. It determines the elasticity of the skin, as it consists of intertwined elastic and collagen fibers. The reticular layer contains sebaceous and sweat glands and hair follicles. The sebaceous glands, starting in the skin itself, open into ducts in the hair follicles. The fats they produce lubricate the hair and soften the skin, giving it elasticity. Sweat glands look like long convoluted tubes, the lower part of which forms a glomerulus. The ducts of the sweat glands open on the surface of the skin. There are about 2-3 million sweat glands in human skin, and they are unevenly distributed. Most of them are found on the palms, soles of the feet and in the armpits. Sweat contains about 98% water, 0.5% urea, 1.5% salts. Among them, sodium chloride predominates, which causes the salty taste of sweat. On average, about 1 liter is released per day. sweat, and in hot climates and hot shops - up to 8-10 liters. Consequently, thanks to the sweat glands, the skin performs an excretory function.

The lower layer of the skin itself passes into the subcutaneous tissue. This layer consists of bundles of connective tissue fibers, and the spaces between them are filled with lobules of adipose tissue. The thickness of the layer depends on lifestyle, nutrition, and metabolic status. This layer regulates the heat exchange of the body, softens pressure and shock to adjacent tissues, is a reserve material that is consumed during fasting, and so on.

The role of the skin in thermoregulation of the body. Thermoregulation is the balancing of heat production in the body with its release to the external environment. Due to exothermic reactions occurring in the body, a large amount of heat is generated. However, there is no increase in body temperature. The constancy of the body's temperature is maintained thanks to thermoregulation mechanisms, leading to an increase or decrease in heat formation, heat release, which occurs with the participation of the skin, nervous system, etc. Heat transfer occurs by conducting heat, radiating it and evaporating sweat, mainly from the surface of the skin (about 2000 cal out of 2500). Thermoregulation is carried out by reflex. When the air temperature rises or falls, the skin receptors that perceive heat or cold are irritated. Excitation is transmitted along centripetal nerves to the brain, and from there through centrifugal nerves to the vessels of the skin.

At low ambient temperatures, skin vessels narrow, the amount of blood circulating through them decreases, and the skin turns pale. At the same time, sweating decreases or stops, which reduces heat loss. As the ambient temperature rises, blood circulation through the vessels of the skin increases, blood vessels dilate, heat transfer increases, and the skin turns red.

If the air temperature approaches body temperature, then sweating remains the only way to transfer heat. In dry weather and windy conditions, sweat evaporates easily. High humidity interferes with evaporation. People in these conditions suffer greatly from the heat. Heat transfer also increases with increased heat generation, which is especially noticeable during physical activity.

Hardening the body is of great importance, as it increases the body’s resistance to cooling. Hardening prevents colds, improves blood circulation, metabolism, increases the tone of the circulatory system, and therefore improves mental and physical performance. Hygienic requirements for hardening are taking into account individual characteristics, gradually increasing the duration and strength of procedures, regularity and mandatory medical supervision. Hardening is carried out through air (air baths), water procedures (rubbing, washing up to the waist, dousing, showering, bathing) and through the sun (sunbathing). The general rule is to start with small doses and not very low temperatures, with a gradual increase in time and decrease in temperature. Proper hardening has a healing effect, but violation of the hardening regime can lead to deterioration in well-being and performance. Hardening should be combined with physical education and sports. A person's fitness also increases resistance to adverse environmental factors.

Hygienic requirements for clothing and footwear. Clothing plays a big role in hygiene. Clothing can help increase or decrease heat transfer, i.e. clothing is an additional regulator of body heat exchange. The air temperature under it should be +28-32?, and the relative humidity - 20-40%. In winter, it is recommended to wear dark clothing, which helps absorb heat, and in summer, light clothing, as it reflects the sun's rays. For winter, woolen items, which conduct heat poorly, are recommended, and in summer, chintz and linen, which have good thermal conductivity, are recommended. Shoes should not be tight, as this restricts blood circulation. Narrow, tight shoes lead to frostbite in winter and scuffs in summer. The best material for shoes is animal leather; it is waterproof and retains heat well. Shoes must match the size and shape of your feet. Tight shoes containing irregularities lead to abrasion of the skin and the formation of inflammation and calluses. The height of the heels should be such as not to impede movement.

PREVENTION AND FIRST AID FOR

ACCIDENTS

Heatstroke can occur when there is general significant overheating of the body at high temperatures and significant humidity. It can happen in cloudy, but hot and windless weather, as well as during prolonged hard physical work. Strong heat transfer is unfavorable for the body, as it leads to increased heart rate, increased breathing, and increased sweating (up to 4-5 liters). In severe cases, severe headache, nausea, cramps and fainting occur. In this case, due to profuse sweating, the salt content in organs and tissues sharply decreases. Heatstroke can be accompanied by an increase in temperature up to +40-41 0 C. When providing assistance, the victim must be kept calm and provided with plenty of cold water to drink to increase sweating. Ice is placed on the head, the body is moistened, and mustard plasters are applied to the legs.

If you are exposed to the sun for a long time or work in hot weather outdoors, sunstroke may occur. To avoid sunstroke, you must wear a hat or a light scarf to protect your head from the sun; there are also special protective devices. During agricultural work, during the hottest time, you need to take a break in the middle of the day.

Frostbite can occur in severe frost and wind. Most often the nose, ears, fingers and toes are subject to frostbite, i.e. organs are less well supplied with blood. The victim should be placed in a warm room, the frostbitten area should be rubbed until red, restoring the flow of blood to the organ. It is recommended to lubricate the skin with fat and make lotions from a 5% solution of potassium permanganate. Severe frostbite requires medical attention.

Burns occur as a result of local exposure to high temperatures, chemicals, electric current or ionizing radiation.

Burns come in different degrees. With a small burn, redness of the damaged area occurs, accompanied by pain. In this case, it is necessary to use some neutralizing solutions. A lotion with a 5% solution of potassium permanganate, lubrication with fat, alcohol, and cologne works well. In severe burns, blisters appear. In this case, a bandage with a solution of potassium permanganate or tannin is recommended. A burn is very dangerous when a large skin surface is damaged. With this type of burn, death can occur not so much from wounds as from self-poisoning of the body. A person with severe burns should be taken to hospital immediately.

Electrical injury (electric shock) can occur through direct contact of the body with a source of electric current, during arc contact, when a person is in close proximity to the current source, but does not touch it, and damage from atmospheric electricity (lightning) can also occur. First aid for electrical injuries must be provided by first ensuring your safety, the main thing is to quickly and skillfully stop the effect of the electric current. It is necessary to turn off the switch and unscrew the safety plugs on the panel. If this is not possible, then the rescuer must release the victim from the current. Pull the wire away from the victim with a dry stick, board or dry rope, after wearing rubber or dry woolen gloves, or wrapping your hands in a dry cloth, your feet should be in galoshes or on a dry board.

If the victim shows signs of clinical death, he is given artificial respiration. If spontaneous breathing is restored, regardless of its condition, the victim should be immediately taken to the hospital.

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 fluid. 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.

During the metabolic process, breakdown products are formed. Some of them are used by the body, others are removed. Carbon dioxide, water, and some volatile substances (alcohol) are removed from the body through the lungs. The intestines secrete undigested food debris, calcium salts, bile pigments, partially water and some other substances. Sweat glands remove 5-10% of all metabolic end products (water, salt, urea, uric acid, etc.).

The main role in excretory processes belongs to the kidneys, which remove from the body about 75% of the final metabolic products (ammonia, urea, uric acid, foreign and toxic substances formed in the body or taken in the form of drugs, etc.). The kidneys, removing excess water and mineral salts from the body, participate in the regulation of the osmotic properties of the blood.

GENITAL SYSTEM

Man, like all living beings on Earth, has the property of self-reproduction, i.e. preservation and continuation of the species (reproduction, reproduction).

In humans, being a dioecious creature, in the process of evolution, male and female reproductive systems were formed. The male reproductive system is represented by two testes, accessory sex glands, seminal vesicles, prostate gland, vas deferens and penis.

Testes (gonads) are glands of mixed secretion, oval in shape, 3-5 cm long, weighing up to 30 g, located outside the body cavity in a special musculocutaneous formation - the scrotum. They consist of convoluted tubules, in the cells of the walls of which male reproductive cells (gametes) are formed - sperm and sex hormones (testosterone, androgens, etc.). These hormones stimulate the growth of the genital organs and the development of sexual characteristics.

The accessory sex glands produce fluid, which is a medium for sperm.

The seminal vesicles and prostate gland produce secretions that mix with sperm to form sperm. There are from 2 to 6 million sperm in 1 cm 3 of sperm. Under an electron microscope, it can be seen that the sperm consists of a head, neck and tail. The head contains the nucleus, and the neck contains a large number of mitochondria. The prostate gland also secretes hormones that regulate cell metabolism - prostaglandins.

The vas deferens is a tube that extends from the scrotum into the abdominal cavity and into the urethra. Serves to remove sperm. The penis serves to introduce sperm into the woman's genital tract. The female reproductive system is formed by two ovaries, fallopian tubes (oviducts), uterus and vagina.

The ovary (gonad) is a mixed secretion gland 3-4 cm long, weighing 6-7 g. It consists of two layers: the outer (cortical) layer serves as the site of formation of eggs (gametes) and sex hormones (progesterone, estrogens). The second layer (brain) is represented by connective tissue, blood vessels and nerves. Each ovary is immersed in fringed funnels that pass into the fallopian tubes, which open into the uterus. The inner surface of the oviducts is lined with ciliated epithelium, the cilia of which, together with contractions of the muscular wall of the oviducts, abdominal and pelvic muscles, propel the egg into the uterus.

The uterus is a hollow, pear-shaped muscular organ. The inner layer of the uterus is a mucous membrane rich in blood vessels. The narrow end of the uterus enters the upper part of the vagina.

The vagina is a muscular tube, covered from the inside with an easily vulnerable mucous membrane, susceptible to various infections. The entrance to the vagina is located between the folds of skin (labia) and is closed by a special connective tissue septum (hymen).

INDIVIDUAL

HUMAN DEVELOPMENT

Individual human development is divided into two periods: intrauterine (embryonic) and extrauterine (postembryonic). The intrauterine period is conventionally divided into 2 periods: 1) embryonic; 2) fetal (fetal).

The embryonic period lasts 8 weeks and includes processes occurring from the moment of fertilization of the egg until the formation of all internal organs. Fertilization occurs in the area of ​​the funnel of the fallopian tube (oviduct). A single-celled embryo is formed - a zygote, in which complex movements of individual sections of the cytoplasm and its organelles occur during the day.

Then, within 3-4 days, the zygote is fragmented through a series of successive mitoses, but without the growth of daughter cells (blastomeres) to the size of the zygote. The result of the cleavage stage is the formation of a multicellular embryo - a morula, which moves into the uterus, where the process of blastulation occurs. The blastomeres in the morula repel each other, shift to the periphery, line up in one layer, and by the 6th day a single-layer embryo in the form of a vesicle is formed. Its cavity (blastocoel) is filled with fluid. The outer layer of blastomeres, called trophoblast, differentiates in one area, forming an inner cell mass (embryoblast). This group of compacted disc-shaped blastomeres forms the so-called embryonic shield. The combination of the trophoblast, the embryonic shield and the cavity is called the germinal vesicle or blastocyst.

Once in the uterine cavity, the blastocyst remains in its cavity for two days. During this time, the egg membrane dissolves, and trophoblast cells come into contact with the cells of the uterine wall. On the 7th day, implantation begins - the immersion of the blastocyst into the uterine mucosa. This process ends by the end of 8 days. In the second week, gastrulation begins, during which embryoblast cells differentiate into three layers: ectoderm, endoderm and mesoderm. At the end of gastrulation in the 4th week, the rudiments of the neural plate and notochord are formed.

During the period of gastrulation, before the appearance of the mesoderm, the embryonic membranes develop. The outer cells of the blastocyst form the outer shell - the chorion, which has villi. In contact with the mucous membrane of the uterus, the chorion ensures the exchange of substances between the body of the mother and the fetus. The outer layer of the germinal disc forms the amnion. This is a thin membrane, the cells of which secrete amniotic fluid, filling the amniotic cavity - the cavity between the amnion and the embryo. The amnion performs a protective function.

A cavity appears in the inner cell mass. The cells lining it give rise to another membrane - the yolk sac.

In humans, the yolk sac contains virtually no yolk; its main function is hematopoiesis. In addition, primary germ cells are formed in its wall, then migrating into the primordia of the gonads.

At the early stages of development, the exchange between the embryo and the maternal organism occurs due to the trophoblast villi, and then the fourth shell, the allantois, develops. The allantois grows in an outward direction until it comes into contact with the chorion, forming a structure rich in vessels that participates in the formation of the placenta. The placenta has the form of a disc embedded in the uterine mucosa, and from the 12th week of development it fully ensures the exchange between the fetus and the mother. By the end of the 8th week, the laying of all internal organs occurs. Tissues are formed and differentiated from the cellular material of embryonic rudiments. The embryonic period ends. An eight-week embryo has a length of 3-3.5 cm, weighs about 4 g. Its neck is formed, facial features are outlined, limbs and external genitalia are formed.

From the 9th week, the fetal period of intrauterine life begins with the predominance of growth processes and final tissue differentiation. By the end of 3 months, the fetus weighs about 40 g, its length reaches 8-9 cm. Nail development begins, ossification nuclei appear in almost all bones. In the 4th month, individual facial features are formed. In the 5th month, the skin becomes covered with fluff, the movements of the fetus are felt by the mother; The fetal heartbeat is heard, which is more frequent than that of the mother. By the end of the 9th month, the fluff on the skin is lost, but a layer of cheese-like lubricant remains; nails protrude above the fingertips, arms are longer than legs; In boys, the testicle descends into the scrotum.

The development of the fetus ends with childbirth (expulsion of the fetus and placenta from the uterus). The onset of labor is associated with the release of the hormone oxytocin by the pituitary gland, which causes strong contractions of the muscles of the uterus and abdominal muscles. The baby is pushed into the pelvis and is born. The first sign of pulmonary respiration is a cry. After 15-20 minutes, the placenta and amniotic membrane are separated from the uterine wall and pushed out.

During the process of embrygenesis, various factors can influence the developing organism (poisons, radiation, vitamin deficiencies, oxygen starvation, etc.) and cause developmental deviations in the form of anomalies and deformities. Violation of living conditions is especially dangerous if it coincides with periods of increased sensitivity of the embryo, the so-called critical periods of embryogenesis.

In humans, the 7th day, 7th week and childbirth are considered critical periods. Therefore, a pregnant woman must be protected from any adverse effects from the very first days of pregnancy.

From the moment of birth to death, extrauterine (postembryonic, postnatal) development lasts.

The following periods are distinguished: newborns (the first 4 weeks after birth); infant (from 1 to 12 months); nursery (from 1 year to 3 years); preschool (from 3 to 6 years); school, or puberty (from 6 to 17-18 years); period of maturity and period of aging.

The most intensive growth and development of a child is observed in the first year of life and during puberty. During the process of growth and development, the proportions of the body change. For example, the ratio of head to body size in a newborn is 1:4, while in an adult it is 1:8.

The main features of humans, in comparison with animals, are the presence of thinking, speech and motor activity, which is closely related to work activity. For the development of these functions, proper upbringing of children aged 2 to 4 years is very important. The period of time from seven to 18 years of age is a decisive period for the physical, mental and moral development of a person.

During puberty, under the influence of sex hormones, secondary sexual characteristics develop (a set of structural features of the body and organ functions that distinguish one sex from another). In girls, they manifest themselves in the form of the development of the mammary glands, an increase in the width of the hips, the deposition of subcutaneous fatty tissue, the appearance of menstruation, etc. In boys, the formation of a narrow pelvis, stronger development of the skeleton and muscles, the growth of a mustache and beard, a change in the timbre of the voice, and the appearance of protruding cartilage are noted on the larynx (“Adam’s apple”), etc. The formation of the human body ends by the age of 22-25.

During the period of maturity, a person is prepared for marriage and reproduction.

The period of aging is characterized by a gradual decrease in the ability of cells to divide, the predominance of dissimilation processes over assimilation, withering of sexual function, and disruption of the normal functioning of all organ systems.

Physical and mental work, physical education, the absence of bad habits (smoking, drinking alcohol or drugs), observing the rules of personal hygiene contribute to the harmonious development of a person and his long life.

BIOLOGISTS

(brief information)

Brown R.(1773-1858) - English botanist, honorary member of the St. Petersburg Academy of Sciences. Described the nucleus of a plant cell and the structure of the ovule. Established the main differences between gymnosperms and angiosperms. Discovered Brownian motion.

Bar K.(1792-1876) – founder of embryology. Born in Estland, worked in Russia. One of the founders of the Russian Geographical Society. Foreign corresponding member (1826) of the Russian Academy of Sciences. Discovered the egg cell in mammals. Described the blastula stage; studied chick embryogenesis. Established the similarity of embryos of higher and lower animals. He discovered that in embryogenesis, characters of a type, class, order, etc. appear sequentially. Described the development of all major organs of vertebrates.

Batson W.(1861-1926) - English biologist, one of the founders of genetics. Foreign corresponding member of the USSR Academy of Sciences. Formulated the hypothesis of gamete purity (1902). He proposed to call the science of variability and heredity genetics (1906), and introduced many genetic terms into it.

Vavilov N. I.(1887-1943) - Soviet scientist, founder of the modern doctrine of the biological foundations of selection and the centers of origin of cultivated plants. Academician of the USSR Academy of Sciences (1929). Organized botanical and agronomic expeditions to the countries of the Mediterranean, North Africa, North and South America. He established ancient centers of the formation of cultivated plants on their territory. He collected the world's largest collection of seeds of cultivated plants. Layed the foundations for state variety testing of field crops. Substantiated the doctrine of plant immunity (1919). Discovered the law of homological series in the hereditary variability of organisms (1920).

Vernadsky V.I.(1863-1945) - Soviet scientist, founder of geochemistry, biogeochemistry, radiogeology. Academician of the USSR Academy of Sciences. Author of works on philosophy, natural science, and scientific studies. The creator of the doctrine of the biosphere and its evolution, the powerful impact of man on the environment and the transformation of the biosphere into the noosphere (sphere of the mind).

Virchow R.(1821-1902) – German pathologist and public figure. Foreign corresponding member of the St. Petersburg Academy of Sciences (1881). He put forward the theory of cellular pathology, according to which the pathological process is the sum of disturbances in the vital functions of individual cells. In 1858 he substantiated the principle of cell continuity by division (“each cell from a cell”).

Haeckel E.(1834-1919) – German evolutionary biologist, representative of natural scientific materialism, supporter and propagandist of the teachings of Charles Darwin. Compiled the first “family tree” of the animal world. He developed a theory of the origin of multicellular organisms from a two-layered ancestor, the gastrula. Formulated the biogenetic law.

Darwin Ch.(1809-1882) - English naturalist, creator of evolutionary theory. Foreign corresponding member of the St. Petersburg Academy of Sciences (1867). In his main work, “The Origin of Species by Means of Natural Selection...” (1859), he summarized the results of his own observations and the achievements of contemporary biology and selection, and revealed the main factors in the evolution of the organic world. In the book “The Origin of Man and Sexual Selection” (1871), he substantiated the hypothesis of the origin of man from an ape-like ancestor.

De Vries X. (1848-1935) - Dutch botanist, one of the founders of the doctrine of variability and evolution. Foreign corresponding member of the Russian Academy of Sciences (1924), foreign honorary member of the USSR Academy of Sciences (1932). Conducted the first systematic studies of the mutation process. Developed the concept of evolution through mutations (De Vries mutation theory). Simultaneously with K.E. Correns and E. Chermak rediscovered Mendel's laws (1900).

Zilber L. A.(1894-1966) - Soviet microbiologist and immunologist, academician of the Academy of Medical Sciences (1945). Described the causative agent of Far Eastern tick-borne encephalitis. Formulated a virogenetic theory of the origin of tumors. Laid the foundations of cancer immunology.

Ivanov M. F.(1871-1935) - Soviet livestock specialist, one of the founders of animal science in the USSR. Academician of the All-Union Academy of Agricultural Sciences named after V.I. Lenin (1935). He developed a scientifically based method for breeding new and improving existing breeds of pigs and sheep. Author of the Askanian breed of sheep and the Ukrainian white breed of pigs.

Ivanovsky D. I.(1864-1920) - Russian scientist, plant physiologist and microbiologist. One of the founders of virology. Discovered the tobacco mosaic virus (1892).

Karpechenko G. D.(1893-1942) – Soviet cytogeneticist. He proved the possibility of overcoming the infertility of distant hybrids through polyploidy. I got a fertile intergeneric radish-cabbage hybrid.

Kovalevsky A. O.(1840-1901) - Russian biologist, one of the founders of comparative embryology and physiology, experimental and evolutionary histology. Academician of the St. Petersburg Academy of Sciences (1890). Established general patterns of development of vertebrates. and invertebrate animals. He extended the doctrine of germ layers to the latter, which proved the mutual evolutionary relationship of these groups of animals. He discovered phagocytic organs in invertebrates and showed their role in the metamorphosis of insects. Kovalevsky's works formed the basis of the phylogenetic trend in biology.

Kovalevsky V. O.(1842-1883) – Russian zoologist, founder of evolutionary paleontology. Follower and propagandist of the teachings of Charles Darwin. He was the first to apply evolutionary teaching in solving problems of vertebrate phylogenesis. Established the relationship between morphology and functional changes and living conditions.

Koltsov N. K. (1872-1940) – Soviet biologist, founder of Russian biology. Corresponding Member of the USSR Academy of Sciences. He developed a hypothesis of the molecular structure and matrix reproduction of chromosomes (“hereditary molecules”), which anticipated the main principles of modern molecular biology and genetics. He is the author of works on comparative anatomy of vertebrates, experimental cytology, and physical and chemical biology.

Creek F.H.K.(b. 1916) – English biophysicist and geneticist. In 1953, together with J. Watson, he created a model of the structure of DNA, thereby proving that it has the form of a double helix. This made it possible to decipher the genetic code, explain many of the properties and biological functions of DNA, and laid the foundation for molecular genetics. Together with J. Watson and M. Wilkins, he is a Nobel Prize laureate (1962).

Lamarck J.B.(1744-1829) - French naturalist, predecessor of Charles Darwin. He is the founder of zoopsychology and the author of “Philosophy of Zoology” (1809), which sets out the first holistic concept of the evolution of living nature. It comes down to the fact that species of animals and plants are constantly changing, becoming more complex in their organization, as a result of the influence of the external environment and some of their internal desire for improvement. However, Lamarck did not reveal the true reasons for evolutionary development.

Linnaeus K.(1707-778) - Swedish naturalist, creator of the system of flora and fauna. Foreign honorary member of the St. Petersburg Academy of Sciences, (1754). For the first time, he consistently applied binary nomenclature and created the most successful artificial classification of plants and animals, describing about 1,500 plant species. He defended the constancy of species and creationism. He is the author of “System of Nature” (1735), “Philosophy of Botany” (1751), etc.

Lobashev M. E.(1907-1971) – Soviet geneticist and physiologist. He mainly conducted research on the study of mutations and recombinations, behavioral genetics, physiology of higher nervous activity and the formation of adaptive reactions in the ontogenesis of animals. He is the author of one of the fundamental textbooks on genetics (1963).

Lomonosov M. V.(1711-1765) - the first Russian scientist-naturalist of world significance, the first Russian academician of the St. Petersburg Academy of Sciences, founder of the first chemical laboratory in Russia. In 1755, on the initiative of M.V. Lomonosov, Moscow University was founded. He developed atom-molecular ideas about the structure of matter. Formulated the principle of conservation of matter and motion. Laid the foundations of physical chemistry. Established the presence of an atmosphere on the planet Venus. Described the structure of the Earth. Explained the origin of many minerals and minerals. He explained natural phenomena from a materialistic point of view. He is the author of works on Russian history.

Mendel G.I.(1822-1884) - Czech naturalist. He is the founder of the doctrine of heredity. He developed a hybridological method, with the help of which he established patterns of distribution in the offspring of hereditary factors, later called genes. G. Mendel's laws were fully confirmed and explained by the chromosomal theory of heredity.

Mechnikov I. I.(1845-191b) - Russian biologist, founder of evolutionary embryology and immunology. Honorary member of the St. Petersburg Academy of Sciences (1902). Together with F. Gamaleya, he founded the first bacteriological station in Russia in 1886. He discovered the phenomenon of phagocytosis (1882). Created a theory of the origin of multicellular organisms. He is the author of works on the problem of aging and a Nobel Prize laureate (1908).

Michurin I. V. (1855-1935) - Soviet biologist and breeder. Honorary member of the USSR Academy of Sciences (1935). He developed methods for the selection of fruit and berry plants, mainly the method of distant hybridization (selection of parental pairs, overcoming inbreeding, etc.). It marked the beginning of the northward movement of many southern cultures. He developed many varieties of fruit and berry crops.

Morgan T.H.(1866-1945) - American biologist, one of the founders of genetics. Laid the foundations of the chromosomal theory of heredity. He established the patterns of gene arrangement on chromosomes, which contributed to the elucidation of the cytological mechanisms of Mendel’s laws and the development of the genetic foundations of the theory of natural selection. He is a Nobel Prize laureate (1933).

Muller F.(1821-1897) – German zoologist. One of the authors of the biogenetic law. He developed many of the teachings of Charles Darwin. He is the author of works on embryology and ecology of invertebrates.

Navashin S. G. (1857-1930) – Soviet cytologist and plant embryologist. Academician of the USSR Academy of Sciences. Discovered double fertilization in angiosperms (1898). Laid the foundations of chromosome morphology and karyosystematics.

Oparin A.I.(1894-1980) – Soviet biochemist, academician of the USSR Academy of Sciences. Created a materialistic theory of the origin of life on Earth (1922). Developed the fundamentals of technical biochemistry in the USSR. Awarded the gold medal named after M.V. Lomonosov of the USSR Academy of Sciences (1980).

Pavlov I. P.(1849-1936) – Soviet physiologist, academician of the USSR Academy of Sciences. Creator of the materialistic doctrine of higher nervous activity. Developed new approaches and methods of physiological research. Author of classic works on the physiology of blood circulation and digestion. He is a Nobel Prize laureate (1904).

Pasteur L.(1822-1895) - French scientist, founder of microbiology and immunology. Honorary member of the St. Petersburg Academy of Sciences. Discovered the nature of fermentation. Refuted the theory of spontaneous generation of microorganisms. Studied the etiology of many infectious diseases. He developed a method of preventive vaccination against chicken cholera (1879), anthrax (1881) and rabies (1885). Introduced methods of asepsis and antiseptics.

Purkina Ya.(1787-1869) - Czech naturalist, foreign corresponding member of the St. Petersburg Academy of Sciences (1836). He discovered the nucleus of the egg cell (1825) and introduced the term “protoplasm”. He is the author of fundamental works on physiology, anatomy, histology and embryology.

Severtsov A. N.(1866-193b) - Soviet biologist, founder of the evolutionary morphology of animals, academician of the USSR Academy of Sciences. Author of the theory of phylembryogenesis, as well as works on the problems of evolutionary morphology and patterns of the evolutionary process.

Sechenov I. M.(1829-1905) - Russian scientist, founder of the physiological school, materialist thinker, honorary member of the St. Petersburg Academy of Sciences. In his classic work “Reflexes of the Brain” (1866), he substantiated the reflex nature of conscious and unconscious activity and showed that psychological phenomena are based on physiological processes that can be studied by objective methods. He discovered the phenomena of central inhibition and the presence of rhythmic bioelectric processes in the central nervous system. Determined the importance of metabolic processes in the implementation of excitation. Investigated the respiratory function of the blood. He laid the foundations of materialistic psychology, labor physiology, developmental, comparative and evolutionary physiology. Sechenov's works had a great influence on the development of natural science and materialist philosophical thought in Russia.

Skryabin K. I.(1878-1972) - Soviet helminthologist, founder of a scientific school, academician of the USSR Academy of Sciences, author of fundamental works on the morphology, systematics, and ecology of helminths in farm animals and humans. Described over 200 new species of helminths. For the first time he raised the question of their pathogenic role and devastation (elimination).

Takhtadzhyan A. L.(b. 1910) - Soviet botanist, academician of the USSR Academy of Sciences (1972), author of works on taxonomy, phylogeny, evolutionary morphology of higher plants, theory of evolution, creator of a new phylogenetic system of plants and botanical-geographical zoning of the Earth.

Timiryazev K. A.(1843-1920) - Russian naturalist-Darwinist, one of the founders of the Russian scientific school of plant physiologists. Revealed the energy laws of photosynthesis. He developed a number of methods for studying plant physiology, the biological foundations of agronomy, and the history of science. He is one of the first propagandists of Darwinism and natural scientific materialism in Russia.

Watson J.D.(b. 1928) - American biochemist, together with F. Crick in 1953, created a model of the spatial structure of DNA in the form of a double helix, which made it possible to explain many of its properties and biological functions. He is a Nobel Prize laureate together with F. Crick and M. Wilkins (1962).

Chetverikov S.S.(1880-1959) - Soviet geneticist, one of the founders of evolutionary and population genetics. He was one of the first to connect the patterns of selection in populations with the dynamics of the evolutionary process.

Schwann T.(1810-1882) - German biologist, founder of cell theory. Based on his own research, as well as the work of M. Schleiden and other scientists, in the classic work “Microscopic studies on the correspondence in the structure and growth of animals and plants” (1839), he first formulated the main principles about the principles of cell formation and the cellular structure of all organisms. He is the author of works on the physiology of digestion, histology, and anatomy of the nervous system. Discovered pepsin in gastric juice (1836).

Schleiden M. Ya.(1804-1881) - German botanist, founder of the ontogenetic method in botany, foreign corresponding member of the St. Petersburg Academy of Sciences (1850). Schleiden's works played an important role in Schwann's development of the cell theory.

Shmalhausen I. I. (1884-1963) - Soviet biologist, theorist of evolutionary theory, academician of the USSR Academy of Sciences (1935). Author of works on comparative anatomy, evolutionary morphology, patterns of animal growth, factors and patterns of biocybernetics.

BIBLIOGRAPHY

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6. Dogel V.A. Zoology of invertebrates. M., Medicine, 1981.

7. Treasurer V.P. Teachings of V.I. Vernadsky about the biosphere and noosphere. Novosibirsk, 1989.

8. Karuzina I.P. Biology. M., Medicine, 1977.

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10. Raven P., Evert R., Eichhorn S. Modern botany. M., Mir, 1990, vol. 1,2.

11. Roginsky Ya.Ya., Levin M.G. Anthropology. M., 1978.

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13. Sapin M.V., Human Anatomy M., Medicine, 1987, vol. 1,2.

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19. Chebyshev N.V. et al. Biology. M., GOU VUNMC, 2005.

SECTION I................................................... ........................................................ ................ 4

ORIGIN OF LIFE ON EARTH.................................................... ........ 4

Properties of life................................................... ........................................................ .... 8

Non-cellular life forms................................................................... ............................... 13

BASICS OF CYTOLOGY.................................................... .................................... 18

Differences between a plant cell and an animal cell.................................................... ... 26

Chemical composition of the cell................................................... .................................. 26

Inorganic substances........................................................ ........................... 27

Organic substances........................................................ .................................... 27

Enzymes........................................................ ........................................................ ............ 31

Metabolism in the cell......................................................... ..................................... 32

Temporal organization of the cell................................................... ...................... 38

Reproduction of organisms................................................... .................................. 42

Formation of germ cells......................................................... ........................... 45

INDIVIDUAL DEVELOPMENT................................................................. ................ 50

BASICS OF GENETICS................................................... .................................... 59

The importance of genetics for medicine.................................................. .................... 61

Basic patterns of inheritance of traits.................................... 62

Gene and trait, gene interaction................................................... .............. 66

Chromosomal theory of heredity................................................................. ..... 68

Basic patterns of variability................................................................... ..... 72

BREEDING OF PLANTS AND ANIMALS

AND MICROORGANISMS................................................... .................................. 78

Plant breeding........................................................ ............................................... 79

Animal selection......................................................... ........................................... 82

Selection of microorganisms................................................... ........................... 83

EVOLUTIONARY TEACHING................................................................. ........................... 85

Pre-Darwinian period................................................... .................................... 85

Darwinian period................................................... ..................................... 88

Socio-economic and scientific prerequisites for the emergence of Darwinism 88

The main provisions of the teachings of Charles Darwin.................................................... ......... 89

View. Population – unit of species.................................................... ....................... 91

Driving forces of evolution................................................................... ................................ 95

Microevolution and macroevolution............................................................ ................. 99

The modern system of flora and fauna on Earth.... 101

DEVELOPMENT OF THE ORGANIC WORLD.................................................... ..... 103

Evidence of the evolution of the organic world.................................................... 103

Aromorphoses in the evolution of the organic world. ..................................... 107

Morphological patterns of evolution.................................................... 107

HUMAN ORIGINS................................................ ............... 112

Driving forces of anthropogenesis.................................................... .................... 116

BASICS OF ECOLOGY................................................... ................................... 119

Biogeocenosis......................................................... ........................................................ ..... 128

FUNDAMENTALS OF THE TEACHING ABOUT THE BIOSPHERE.................................................... ............... 132

SECTION II................................................... ........................................................ ......... 138

SYSTEMATIC REVIEW OF THE ORGANIC WORLD.................................. 138

SUB-EMPIRE PRE-NUCLEAR ORGANISMS. KINGDOM

REAL BACTERIA.................................................... ........................... 138

SUB-EMPIRE NUCLEAR ORGANISMS

(EUKARYOTES)......................................................... ........................................................ .. 144

Kingdom of Protoctista................................................... .................................... 144

Kingdom of Mushrooms................................................ ........................................................ 147

Department Lichens......................................................... ........................................... 151

KINGDOM OF PLANTS................................................... .................................... 154

Spore plants........................................................ ........................................... 154

Seed plants........................................................ ........................................... 161

CLASSIFICATION OF FLOWERING PLANTS.................................................... 183

General characteristics of the class Dicotyledonous plants.................................... 183

General characteristics of the class Monocots.......................... 183

ANIMALS................................................. ........................................................ .... 184

GENERAL CHARACTERISTICS OF THE TYPE PROTOZOO.................................... 185

General characteristics of the Sarcodaceae class.................................................... 188

General characteristics of the class Flagellates.................................................... 190

General characteristics of the class Sporozoans.................................................. 193

General characteristics of the Ciliates class.................................................... .196

GENERAL CHARACTERISTICS OF THE TYPE CELINETARY........ 199

GENERAL CHARACTERISTICS OF THE TYPE FLATWORMS.................................... 202

General characteristics of the Ciliary class.................................................... .. 203

General characteristics of the Flukes class.................................................... 205

General characteristics of the class Tapeworms.................................................... 209

GENERAL CHARACTERISTICS OF THE TYPE ROUNDWORMS.................................... 211

GENERAL CHARACTERISTICS OF THE TYPE ANNELED WORMS.................. 215

GENERAL CHARACTERISTICS OF THE TYPE ARTHOPOD.................................... 217

General characteristics of the class Crustaceans.................................................... 219

General characteristics of the Arachnida class.................................................... 221

General characteristics of the class Insects.................................................... .224

GENERAL CHARACTERISTICS OF THE MOLLUSCA TYPE.................................... 229

General characteristics of the class Gastropods.................................................... 232

General characteristics of the class Bivalve.................................................... 233

GENERAL CHARACTERISTICS OF THE TYPE CHORDATES.................................................... 235

General characteristics of the Lancelet class.................................................... 236

General characteristics of the class Bony fish.................................................... 239

General characteristics of the class Amphibians.................................................... 242

General characteristics of the class Reptiles.................................... 246

General characteristics of the Bird class.................................................... .......... 250

General characteristics of the class Mammals.................................................... 254

SECTION III................................................... ........................................................ ........ 258

HUMAN ANATOMY AND PHYSIOLOGY.................................................... 258

TISSUE, THEIR STRUCTURE AND FUNCTION, ORGAN SYSTEMS......... 259

Epithelial tissues........................................................ .................................... 260

Connective tissues........................................................ .................................... 261

Muscle tissue......................................................... ............................................... 265

Nervous tissue......................................................... ........................................................ .. 265

SKIN, ITS STRUCTURE AND FUNCTIONS.................................................... ............ 267

The role of the skin in thermoregulation.................................................................... ........................... 269

Skin hygiene................................................... ........................................................ .... 271

NERVOUS SYSTEM................................................ .................................... 271

Structure and functions of the spinal cord................................................................. ............. 272

Structure and functions of the brain.................................................... .......... 274

Peripheral nervous system................................................................... ............... 277

ANALYZERS. SENSE ORGANS................................................... ........ 278

HIGH NERVOUS ACTIVITY.................................................... .. 285

Hygiene of mental work................................................................... ........................ 289

ENDOCRECTION GLANDS.................................................................... .......... 290

The processes of excretion of metabolic end products from the body in ixodid and argasid ticks, as in other groups of periodically feeding blood-sucking arthropods, are subject to the periodicity of the gonotrophic rhythm of the imago and molting cycles of immature phases. In addition to excretory products, the rectal bladder, with the exception of some species of argasids (Ornithodoros moubata), receives the products of digestion of the host's blood and the decaying cells of the midgut, and during feeding there is a significant amount of slightly changed blood. As a result, tick feces are a mixture of several substances, the ratio between which changes at different periods of the life cycle.
Composition of excreta. The end product of nitrogen metabolism in mites is guanine (Schulze, 1955; Kitaoka, 1961c), and in this respect they are similar to other arachnids (Schmidt a. oth, 1955). Guanine has very low solubility and precipitates even at low concentrations. As a result, in the Malpighian vessels and rectal bladder it is found predominantly in the form of a suspension or mushy mass of crystals, the removal of which from the body requires a small amount of water. During the period of embryogenesis, molting or prolonged starvation, when ticks are deprived of the opportunity to receive a sufficient amount of water from the outside, the poor solubility of guanine allows for its progressive accumulation in the Malpighian vessels and prevents an increase in its concentration in the hemolymph to toxic values.
Guanine crystals are bright white in color and glow intensely in polarized light. In the contents of the Malpighian vessels and rectal bladder, one can distinguish small (2-4 μm), irregularly shaped, medium (10-20 μm) and large (40-80 μm) spherites by appearance. The latter are distinguished by well-defined concentric layering and can be simple, double or complex, that is, glued together from several simple ones (Fig. 63). In addition to guanine spherites, in the Malpighian vessels of feeding individuals there are quite numerous spherical bodies up to 100 μm in size, formed from smaller eosinophilic balls. The latter reach a diameter of 1-3 microns and are simultaneously found in the cytoplasm of cells.
Functioning of the Malpighian vessels. The biochemical pathways of guanine synthesis, as well as the place of its formation in the body of ticks, require further special research. At the same time, intravital observations of prepared Malpighian vessels and viewing of serial sections of mites Argas persicus, Ornithodoros papillipes (nymphs, females and males), Hyalomma asiaticum and Ixodes ricinus (larvae, nymphs and females) made it possible to identify the rhythm of the excretory organs.
Argasid mites. In Argasid mites that have recently molted or been starved for a long time, the lumen of the Malpighian vessels contains a large number of guanine spherites, and the wall cells are moderately flattened (Fig. 335 p. 193). After molting, only partial unloading of the vessels from guanine occurs, and subsequently, before feeding, they are again gradually filled with excrement. Immediately after feeding, almost complete removal of guanine from the vascular cavity is observed (unloading phase; Fig. 336). At the same time, the height of the epithelial cells of the walls increases, probably actively participating in the excretion of metabolic products, which must accumulate in large quantities as a fresh portion of protein food is digested. For several days after feeding, the release of guanine into the lumen of the vessels does not lead to their filling with spherites due to the rapid leaching of the latter into the rectal bladder and frequent bowel movements. Later, the supply of water obtained with the host’s blood is exhausted, the intensity of defecation weakens, and the lumen of the vessels is again gradually filled with guanine (loading phase) until the next blood sucking.
Ixodid ticks. In newly moulted females of Hyalomma asiaticum and Ixodes ricinus, the Malpighian vessels are filled with a large number of guanine spherites. They are unloaded from excreta accumulated during the period of preparation for molting within 1-3 days after molting. Subsequently, at the stage of post-molting development, the lumen of the vessels contains a small number of single small and medium-sized spherites that do not form local clusters. The diameter of the vessels ranges from 50 to 70 microns and they look almost transparent.
Epithelial cells are moderate in size, cubic or slightly flattened (Fig. 342).
In starving individuals, before attachment to the host, a slow loading of the vascular cavity with guanine spherites is observed. The latter form

Rice. 342-348. Transverse sections of Malpighian vessels of a female Ixodes ricinus at different stages of the life cycle.
342 - at the stage of post-molting development; 343 - after 1 year of fasting; 344 - on the third day of attachment, weight 10 mg; 345 - the same, area loaded with guanine; 346 - nourished immediately after falling away; 347 - before the start of oviposition; 348 - before the end of oviposition.
i - nuclei of epithelial cells; mf - muscle fibers; c - vacuoles; g - guanine spherites.
along the vessels there are local accumulations (Fig. 338), so that there is an alternation of optically empty and white (with guanine) areas. The diameter of the vessels does not change significantly. The cells of the walls retain their previous sizes (Fig. 343).
After the ticks attach to the host, in the first 1-3 days, the vessels are cleared of excreta accumulated during fasting and they become translucent along their entire length (Fig. 339). At the same time, the size of the epithelial cells increases noticeably and their apical ends in some places protrude into the lumen (Fig. 344-345). The diameter of the vessels increases by 1.5-2 times. The protoplasm in the apical zone becomes vacuolated and in some places eosinophilic inclusions appear in it. The size of the nuclei increases noticeably. Mitotic divisions resume, but their number is less than in preparation for molting. The size of the cells continues to increase until the end of feeding and sometimes rod-shaped striations are revealed along their apical border. Some cells undergo partial destruction (rejection of apical sections of the cytoplasm) or even complete destruction.
Gradually, due to the intensification of digestion, the rate of guanine deposition in the Malpighian vessels begins to exceed the rate of its excretion into the rectal bladder. Guanine spherites begin to form local accumulations again (Fig. 340). By the time feeding ends, the lumen of the vessels is already filled with guanine throughout and the organs acquire their characteristic milky-white color. The walls of the vessels are not yet subject to noticeable stretching, and guanine spherites float freely in their liquid contents. The diameter of the vessels of engorged individuals is 3-4 times greater than that of hungry individuals (Fig. 346). Such growth is achieved almost exclusively through the growth and proliferation of epithelial cells.
After falling off the host, the process of loading the vessels with guanine continues with even greater intensity. Their diameter at this stage can increase 10 times compared to hungry individuals. They are literally filled throughout their entire length with a continuous mass of guanine, which greatly stretches their walls (Fig. 346-348). The rectal bladder at this stage is also unusually enlarged and clogged with guanine alone.
In larvae and nymphs, the processes of functioning of the Malpighian vessels proceed similarly to females. However, they do not have such a strong filling of guanine due to the periodic release of excreta during and after feeding. In preparation for rectal molting, communication between the rectal bladder and the external environment is interrupted. From this moment until the end of the moult, there is no bowel movement. The connection between the Malpighian vessels and the rectal bladder, on the contrary, is not disrupted and large amounts of guanine continuously enter it. The size of the rectal bladder increases unusually towards the end of molting and it occupies most of the posterior half of the body cavity. Guanine spherocrystals accumulating in it in huge quantities stretch the walls to the state of a membrane-like shell with randomly scattered flattened nuclei.
The stretching of the walls of the Malpighian vessels even during molting, in contrast to engorged females, remains very insignificant (Fig. 337). Peristaltic contractions of the vessels push the guanine accumulating in them into the rectal bladder. The length and diameter of the vessels increase significantly due to division and growth of the cells of their walls (Fig. 382). As a result, the number of nuclei per transverse section through the Malpighian vessel increases from 1-2 in larvae to 3-4 in nymphs and
5-8 in females.
In Argasid mites, according to the observations of L.K. Efremova (1967) on nymphs of Alveonasus lahorensis, cell division of the Malpighian vessels and organ growth are observed at the molting stage. However, unlike ixodids, the last moult in the imaginal phase is not associated with cell division of the Malpighian vessels. In adult argasids, the size of the Malpighian vessels no longer changes and there are no cell divisions in their walls. The increase in cell size in feeding individuals is possibly associated with the processes of their polyploidization. The polyploid nature of the nuclei of these organs can be judged by the appearance of tetraploid sets of chromosomes in dividing cells, but the mechanism of this process has not been studied.
Rhythm of defecation. The release of the rectal bladder from the guanine and blood digestion products that accumulate in it occurs with a certain cyclicity. In adult Argasid mites, the largest amount of excretory products is excreted in the first days after molting and then within 1-5 days after bloodsucking. At the same time, acts of defecation do not stop throughout the entire gonotrophic cycle and are accompanied by the release of a small mass of feces consisting, without any particular pattern, of guanine (white color), hematin or a mixture of both (black color). Larvae and nymphs behave in a similar manner, but their fecal excretion is constantly interrupted for a period of several days to several weeks before molting.
In adult ixodid ticks, the maximum amount of guanine is excreted in the first days after molting and during feeding, and in larvae and nymphs, in the first few days after its completion. In females, after falling off the host, defecation immediately stops and the accumulated excreta remains in the body until the death of the tick.
In engorged larvae and nymphs, defecation is interrupted as the hypodermis begins to separate from the old cuticle.
The consistency of feces varies depending on the water content in the body. During feeding or immediately after it, they are more liquid, whereas in hungry individuals they are almost dusty. Apparently, like some other representatives of arthropods, the cells of the rectal bladder are capable of partial readsorption of water.

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.