home Calculators Physiology of the excretory organ system. Excretory system

Physiology of the excretory organ system. Excretory system

The human excretory system is a filter for the body.

The human excretory system is a set of organs that remove excess water from our body, toxic substances, final products exchange, salts formed in the body or entering it. We can say that the excretory system is a filter for the blood.

The organs of the human excretory system are the kidneys, lungs, gastrointestinal tract, salivary glands, and skin. However, the leading role in the process of life belongs to the kidneys, which can remove up to 75% of substances harmful to us from the body.

This system consists of:

Two kidneys;

Bladder;

The ureter, which connects the kidney and bladder;

The urethra or urethra

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

Functions of the human excretory system

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

2. The human excretory system serves to provide water-salt balance, that is, regulate the amount of salts and liquids, ensuring a constant internal environment. The kidneys resist an increase in the norm of the amount of water and thereby an increase in pressure.

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

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

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

6. The levels of phosphorus and calcium in the body are regulated.

The structure of the human excretory system

Each person has a pair of kidneys, which are located in the lumbar region on either side of the spine. Usually one of the kidneys (the right one) is located slightly lower than the second. They are shaped like beans. On inner surface the kidneys are the gates through which nerves and arteries enter and exit lymphatic vessels, veins and ureter.

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

Urination

Before it is formed, urine goes through 3 stages:

Glomerular filtration,

Secretion

Tubular reabsorption.

Filtration proceeds as follows: due to the pressure difference, water leaks from the human blood into the capsule cavity, and with it most of the dissolved low-molecular substances ( mineral salts, glucose, amino acids, urea and others) As a result of this process, primary urine appears, which has a weak concentration. During the day, the blood is filtered many times by the kidneys, and about 150-180 liters of liquid is formed, which is called primary urine. Urea, a number of ions, ammonia, antibiotics and other metabolic end products are additionally released into the urine with the help of cells located on the walls of the tubules. This process is called secretion.

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

Urination

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

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

We can say that the human excretory system is represented by a collection of many organs that have a close connection with each other and complement each other’s work.

Organs of the excretory system include kidneys, which form urine, and urinary tract- ureters, bladder and urethra.

Kidneys

Kidneys- main organs of the excretory system; their main function is to maintain homeostasis in the body, including: 1) removing metabolic end products and foreign substances from the body; 2) regulation of water-salt metabolism and acid-base balance; 3) regulation blood pressure; 4) regulation of erythropoiesis; 5) regulation of calcium and phosphorus levels in the body.

The kidneys are surrounded by fatty tissue (fat capsule) and covered with thin fibrous capsule made of dense fibrous connective tissue containing smooth muscle cells. Each kidney consists of an externally located cortex and lying inside medulla(Fig. 244).

Kidney cortex (renal cortex) located in a continuous layer under the capsule of the organ, from it into the medulla between renal pyramids are being sent renal pillars(Bertin). The cortex is represented by areas containing renal corpuscles and crimped renal tubules(forming cortical labyrinth), which alternate with brain rays(see Fig. 244), containing straight renal tubules and collecting ducts (see below).

Kidney medulla consists of 10-18 conical renal pyramids, from the base of which they penetrate into the cortex brain rays. Tops of the pyramids (renal papillae) addressed to small cups, of which urine enters through two or three large cups V renal pelvis - dilated upper part of the ureter emerging from renal hilum The pyramid with the area of cortex covering it form renal lobe, and the medullary ray with the surrounding cortex - renal (cortical) lobule(see Fig. 244).

Nephron is the structural and functional unit of the kidney; Each kidney contains 1-4 million nephrons (with significant individual variations). The nephron (Fig. 245) includes two parts that differ in their morphofunctional characteristics - renal corpuscle And renal tubule, which consists of several departments (see below).

Renal corpuscle provides a process of selective filtration of blood, which results in the formation primary urine. It has a round shape and consists of vascular glomerulus, covered with two layers glomerular capsule(Shumlyansky-Bowman) (Fig. 247). The renal corpuscle has two poles: vascular(in the area where the afferent and efferent arterioles are located) and uric(at the origin of the renal tubule).

Glomerulus formed by 20-40 capillary loops, between which there is a special connective tissue - mesangium.

Glomerular capillary network educated fenestrated endothelial cells, lying on the basement membrane, which in most areas is common with the cells of the visceral layer of the capsule (Fig. 248 and 249). Pores in the cytoplasm of endothelial cells occupy 20-50% of their surface; some of them are closed with diaphragms - thin protein-polysaccharide films.

Mesangium comprises mesangial cells (mesangiocytes) and the intercellular substance located between them - mesangial matrix. The mesangium of the glomerulus passes into perivascular island of mesangium (extraglomerular mesangium)(see Fig. 247).

Mesangial cells - branched, with a dense core, well-developed organelles, big amount filaments (including contractile ones). They are connected to each other by desmosomes and gap junctions. Mesangial cells play the role of elements that support the capillaries of the glomerulus, contract, regulate blood flow in the glomerulus, have phagocytic properties (absorb macromolecules that accumulate during filtration, participate in the renewal of the basement membrane), produce mesangial matrix, cytokines and prostaglandins.

Mesangial matrix consists of a basic amorphous substance and does not contain fibers. It has the appearance of a three-dimensional network, its composition is similar to the material of the basement membrane - it includes glycosaminoglycans, glycoproteins (fibronectin, laminin, fibrillin), proteoglycan perlecan, collagens of types IV, V and VI, it lacks fiber-forming collagens of types I and III.

Glomerular capsule formed by two leaves of the capsule (parietal and visceral, separated by a slit capsule cavity(see Fig. 247).

Parietal leaf represented by single-layer squamous epithelium, which passes into the visceral

the ceral layer in the region of the vascular pole of the body and into the epithelium of the proximal part - in the region of the urinary pole.

Visceral leaf, covering the capillaries of the glomerulus, formed by large branched epithelial cells - podocytes(see Fig. 247-249). From their body, containing well-developed organelles and protruding into the cavity of the capsule, long and wide primary processes (cytotrabeculae), branching into secondary ones, which can give rise to tertiary ones. All processes form numerous outgrowths (qi topodia), which interdigitate with each other on the surface of the capillaries, the spaces between them (filtration slots) closed thin slot diaphragms with transverse striations (similar in appearance to a “zipper”) and a compacted longitudinal filament in the center (see Fig. 248 and 249).

basement membrane - very thick, common to the endothelium of capillaries and podocytes, results from the fusion of the basement membranes of endothelial cells and podocytes. It is formed by three records(layers): outer and inner transparent(sparse) and central dense(see Fig. 248 and 249).

Filtration barrier in the glomerulus is a set of structures through which blood is filtered to form primary urine. The permeability of a filtration barrier for a particular substance is determined by its mass, charge and configuration of its molecules. The barrier consists of (see Fig. 248 and 249): (1) cytoplasm of fenestrated endothelial cells glomerular capillaries; (2) three-layer basement membrane;(3) slit diaphragms, closing filtration gaps (between the cytopodia of the podocyte).

Renal tubule includes proximal tubule, thin tubule of nephron loop, distal tubule.

Proximal tubule provides obligate reabsorption into the peritubular capillaries of most (80-85%) of the volume of primary urine with reabsorption of water and useful substances and accumulation of metabolic end products in the urine. It also secretes certain substances into the urine. The proximal tubule includes proximal convoluted tubule(located in the cortex, has the greatest length and is most often detected on sections of the cortex) and proximal straight tubule(descending thick part of the loop); it starts from the urinary pole of the glomerular capsule and abruptly passes into the thin segment of the nephron loop (see Fig. 245 and 247). Looks like a thick tube formed single-layer cubic epithelium. Cytoplasm

cells - vacuolated, granular, stained oxyphilic and contains well-developed organelles and numerous pinocytotic vesicles transporting macromolecules. On the apical surface of epithelial cells there is a brush border, increasing its surface area by 20-30 times. It consists of several thousand long (3-6 microns) microvilli. In the basal part of the cells, the cytoplasm forms intertwined processes (basal labyrinth), inside of which elongated mitochondria are located perpendicular to the basement membrane, which creates a picture at the light-optical level "basal striation"(see Fig. 3, 246, 250).

Thin tubule of the nephron loop together with the fat one (distal straight tubule) ensures urine concentration. It is a narrow U-shaped tube consisting of thin descending segment(V nephrons with a short loop - cortical), and also (in nephrons with a long loop - juxtamedullary)- thin upstream segment(see Fig. 245). The thin tubule is formed by flat epithelial cells (slightly thicker than the endothelium of adjacent capillaries) with poorly developed organelles and a small number of short microvilli. The nuclear-containing part of the cell protrudes into the lumen (see Fig. 246 and 251).

Distal tubule participates in the selective reabsorption of substances and transports electrolytes from the lumen. It includes distal straight tubule(the ascending thick part of the loop), distal convoluted tubule And communication tubule(see Fig. 245). The distal tubule is shorter and thinner than the proximal one and has a wider lumen; it is lined with a single-layer cubic epithelium, the cells of which have light cytoplasm, developed interdigitation on the lateral surface and a basal labyrinth (see Fig. 3, 246 and 250). There is no brush border; pinocytotic vesicles and lysosomes are few in number. The distal straight tubule returns to the renal corpuscle of the same nephron and in the region of its vascular pole is modified, forming dense spot - Part juxtaglomerular complex(see below).

Collecting ducts(see Fig. 244-246, 250 and 251) are not part of the nephron, but are closely related to it functionally. They participate in maintaining water-electrolyte balance in the body, changing their permeability to water and ions under the influence of aldosterone and antidiuretic hormone. They are located in the cortex (cortical collecting ducts) and medulla (cerebral collecting ducts) forming a branched system. Lined with cubic epi-

telium in the cortex and superficial parts of the medulla and columnar in its deep parts (see Fig. 33, 244, 246, 250 and 251). The epithelium contains two types of cells: (1) main cells(light) - numerically predominant, characterized by poorly developed organelles and a convex apical surface with a long single cilium; (2) intercalary cells(dark) - with dense hyaloplasm, a large number of mitochondria, multiple microfolds on the apical surface. The largest of the cerebral collecting ducts (diameter - 200-300 microns), known as papillary ducts(Bellini), open papillary openings on renal papilla V lattice zone. They are formed by tall columnar cells with convex apical poles.

Types of nephrons are distinguished based on the characteristics of their topography, structure, function and blood supply (see Fig. 245):

1)cortical (short loop) make up 80-85% of nephrons; their renal corpuscles are located in the cortex, and relatively short loops (not containing a thin ascending segment) do not penetrate the medulla or end in its outer layer.

2)juxtamedullary (long loop) make up 15-20% of nephrons; their renal corpuscles lie near the cortico-medullary border and are larger than those in the cortical nephrons. The loop is long (mainly due to the thin part with a long ascending segment), penetrates deeply into the medulla (to the top of the pyramids), ensuring the creation of a hypertonic environment in its interstitium, necessary for concentrating urine.

Interstitium- the connective tissue component of the kidney, surrounding in the form of thin layers the nephrons, collecting ducts, blood and lymph vessels and nerve fibers. It performs a supporting function, is an area of interaction between nephron tubules and blood vessels, and is involved in the production of biologically active substances. It is more developed in the medulla (see Fig. 251), where its volume is several times greater than in the cortex. Formed by cells and intercellular substance, which contains collagen fibers and fibrils, as well as a ground substance containing proteoglycans and glycoproteins. The cells of the interstitium include: fibroblasts, histiocytes, dendritic cells, lymphocytes, and in the medulla - special interstitial cells several types, including spindle cells containing lipid droplets that produce vasoactive factors (prostaglandins, bradykinin). According to some data, peritubular interstitial cells grow

They use erythropoietin, a hormone that stimulates erythropoiesis.

Juxtaglomerular complex- a complex structural formation that regulates blood pressure through renin-angiotensin system. It is located at the vascular pole of the glomerulus and includes three elements (see Fig. 247):

Dense spot - a section of the distal tubule located in the space between bringing And efferent glomerular arterioles at the vascular pole of the renal corpuscle. Consists of specialized tall narrow epithelial cells, the nuclei of which lie more densely than in other parts of the tubule. The basal processes of these cells penetrate the discontinuous basement membrane, contacting the juxtaglomerular myocytes. Macula densa cells have osmoreceptor function; synthesize and release nitric oxide, regulating vascular tone afferent and/or efferent glomerular arterioles, thereby affecting renal function.

Juxtaglomerular myocytes (juxtaglomerulocytes) - modified smooth myocytes of the tunica media of the afferent (to a lesser extent, efferent) glomerular arteriole at the vascular pole of the glomerulus. They have baroreceptor properties and, when the pressure drops, they release the hormone synthesized by them and contained in large dense granules. renin Renin is an enzyme that breaks down angiotensin I from blood plasma protein angiotensinogen. Another enzyme (in the lungs) converts angiotensin I to angiotensin II, which increases pressure, causing constriction of arterioles and stimulating the secretion of aldosterone by the zona glomerulosa of the adrenal cortex.

Extraglomerular mesangium - an accumulation of cells (Gurmagtig cells) in a triangular-shaped space between the glomerular arterioles and the macula densa, which passes into the mesangium of the glomerulus. The organelles of the cells are poorly developed, and numerous processes form a network in contact with the cells of the macula densa and juxtaglomerular myocytes, through which they are assumed to transmit signals from the former to the latter.

Blood supply to the kidneys very intensively, which is necessary for the implementation of their functions. At the organ gate renal artery divided by interlobar, running in the renal columns (see Fig. 245). At the level of the base of the pyramids they branch arcuate arteries(run along the cortico-medullary border), from which they extend radially into the cortex interlobular arteries. The latter pass between adjacent medullary rays and give rise to afferent glomerular arterioles,

disintegrating into glomerular capillary network(primary). Blood is collected from the glomerulus efferent arterioles; in cortical nephrons they immediately branch into an extensive network of secondary peritubular (peritubular) fenestrated capillaries, and in the juxtamedullary nephrons they give long thin straight arterioles, going into the medulla and papillae, where they form a network of peritubular fenestrated capillaries, and then, bending in the form of a loop, return to the cortico-medullary border in the form straight venules(with fenestrated endothelium).

Peritubular capillaries of the subcapsular region collect into venules that carry blood to interlobular veins. The latter flow into arcuate veins, connecting with interlobar veins, which form renal vein.

Urinary tract

Urinary tract are partially located in the kidneys themselves (renal calyces, small and large, pelvis), but are mainly located outside it (ureters, bladder and urethra). The walls of all these sections of the urinary tract (with the exception of the last) are built in a similar way - their walls include three membranes (Fig. 252 and 253): 1) mucous membrane (with a submucous base), 2) muscular, 3) adventitial (in the bladder partially serous).

Mucous membrane educated epithelium And own record.

Epithelium - transitional (urothelium) - see fig. 40, its thickness and number of layers increase from the calyces to the bladder and decrease as the organs stretch. It is impermeable to water and salts and has the ability to change its shape. Its surface cells are large, with polyploid nuclei (or bi-

nuclear), changing shape (round in an unstretched state and flat in a stretched state), invaginations of the plasmalemma and fusiform vesicles in the apical cytoplasm (plasmolemma reserves that are built into it during stretching), a large number microfilaments. Epithelium of the bladder in the area of the internal urethral opening (bladder triangle) forms small invaginations into the connective tissue - mucous glands.

Own record formed by loose fibrous connective tissue; it is very thin in the calyces and pelvis, more pronounced in the ureter and bladder.

Submucosa absent in calyxes and pelvis; does not have a sharp border with the lamina propria (which is why its existence is not recognized by everyone), however (especially in the bladder) it is formed by looser tissue with increased content elastic fibers compared to the lamina propria, which contributes to the formation of folds of the mucous membrane. May contain isolated lymphoid nodules.

Muscularis contains two or three vaguely demarcated layers formed by bundles of smooth muscle cells, surrounded by pronounced layers of connective tissue. It begins in the small calyxes in the form of two thin layers - internal longitudinal And external circular. The pelvis and upper part of the ureter contain the same layers, but their thickness increases. In the lower third of the ureter and in the bladder, to the described two layers is added outer longitudinal layer. In the bladder internal hole The urethra is surrounded by a circular muscle layer (internal sphincter of the bladder).

Adventitia- external, formed by fibrous connective tissue; on the upper surface of the bladder is replaced serous membrane.

ORGANS OF THE EXCRETORY SYSTEM

Rice. 244. Kidney (general view)

1 - fibrous capsule; 2 - cortex: 2.1 - renal corpuscle, 2.2 - proximal tubule, 2.3 - distal tubule; 3 - brain ray; 4 - cortical lobule; 5 - interlobular vessels; 6 - subcapsular vein; 7 - medulla: 7.1 - collecting duct, 7.2 - thin tubule of the nephron loop; 8 - arcuate vessels: 8.1 - arcuate artery, 8.2 - arcuate vein

Rice. 245. Scheme of the structure of nephrons, collecting ducts and blood circulation in the kidney

I - juxtamedullary nephron; II - cortical nephron

1 - fibrous capsule; 2 - cortex; 3 - medulla: 3.1 - outer medulla, 3.1.1 - outer stripe, 3.1.2 - inner stripe, 3.2 - inner medulla; 4 - renal corpuscle; 5 - proximal tubule; 6 - thin tubule of the nephron loop; 7 - distal tubule; 8 - collecting duct; 9 - interlobar artery and vein; 10 - arcuate artery and vein; 11 - interlobular artery and vein; 12 - afferent glomerular arteriole; 13 - (primary) glomerular capillary network; 14 - efferent glomerular arteriole; 15 - peritubular (secondary) capillary network; 16 - straight arteriole; 17 - straight venule

Ultrastructural organization of epithelial cells various departments nephron and collecting duct, marked with letters A, B, C, D, is shown in Fig. 246

Rice. 246. Ultrastructural organization of epithelial cells of various parts of the nephron and collecting duct

Drawing with EMF

A - cubic microvillous (bordered) epithelial cell from the proximal tubule: 1 - microvillous (brush) border, 2 - basal labyrinth; B - cubic epithelial cell from the distal tubule: 1 - basal labyrinth; B - flat epithelial cell from a thin tubule of the nephron loop; G - main epithelial cell from the collecting duct

The location of cells in the corresponding parts of the nephron and collecting duct is shown by arrows in Fig. 245

Rice. 247. Renal corpuscle and juxtaglomerular apparatus

Staining: CHIC reaction and hematoxylin

1 - vascular pole of the renal corpuscle; 2 - tubular (urinary) pole of the renal corpuscle; 3 - afferent arteriole: 3.1 - juxtaglomerular cells; 4 - efferent arteriole; 5 - capillaries of the vascular glomerulus; 6 - outer (parietal) leaf of the glomerular capsule (Shumlyansky-Bowman); 7 - internal (visceral) layer of the capsule formed by podocytes; 8 - cavity of the glomerular capsule; 9 - mesangium; 10 - cells of extraglomerular mesangium; 11 - distal tubule of the nephron: 11.1 - dense spot; 12 - proximal tubule

Rice. 248. Ultrastructure of the filtration barrier in the renal glomerulus

Drawing with EMF

1 - podocyte processes: 1.1 - cytotrabecula, 1.2 - cytopodia; 2 - filtration slots; 3 - basement membrane (three-layer); 4 - fenestrated endothelial cell: 4.1 - pores in the cytoplasm of the endothelial cell; 5 - capillary lumen; 6 - erythrocyte; 7 - filtration barrier

Rice. 249. Ultrastructure of the filtration barrier in the renal glomerulus

A - drawing with EMF; B - section of the barrier in three-dimensional reconstruction

1 - podocyte: 1.1 - cytotrabecula, 1.2 - cytopodia; 2 - filtration slits: 2.1 - slot diaphragms; 3 - basement membrane (three-layer); 4 - fenestrated endothelial cell: 4.1 - pores in the cytoplasm of the endothelial cell; 5 - lumen of the glomerular capillary; 6 - erythrocyte; 7 - filtration barrier

The blue arrow indicates the direction of transport of substances from the blood into primary urine during ultrafiltration

Rice. 250. Kidney. Cortical area

Staining: CHIC reaction and hematoxylin

1 - renal corpuscle: 1.1 - choroidal glomerulus, 1.2 - glomerular capsule, 1.2.1 - outer layer, 1.2.2 - inner layer, 1.3 - capsule cavity; 2 - proximal tubule of the nephron: 2.1 - cuboidal epithelial cells, 2.1.1 - basal striation, 2.1.2 - microvillous (brush) border; 3 - distal tubule: 3.1 - basal striation, 3.2 - dense spot; 4 - collecting duct

Rice. 251. Kidney. Area of the medulla

Staining: CHIC reaction and hematoxylin

1 - collecting duct; 2 - thin tubule of the nephron loop; 3 - distal tubule (straight part); 4 - interstitial connective tissue; 5 - blood vessel

Rice. 252. Ureter

Staining: hematoxylin-eosin

1 - mucous membrane: 1.1 - transitional epithelium, 1.2 - lamina propria; 2 - muscular layer: 2.1 - inner longitudinal layer, 2.2 - outer circular layer; 3 - adventitia

Rice. 253. Bladder (bottom)

Staining: hematoxylin-eosin

1 - mucous membrane: 1.1 - transitional epithelium, 1.2 - lamina propria; 2 - submucosa; 3 - muscular layer: 3.1 - inner longitudinal layer, 3.2 - middle circular layer, 3.3 - outer longitudinal layer, 3.4 - connective tissue layers; 4 - serous membrane

1. Why should metabolic products be removed from the body?

The accumulation of metabolic products in the body, such as urea, phosphoric and sulfuric acid, carbon dioxide and others, can lead to self-poisoning of the body, which leads to the development various diseases and human death.

2. What organs are classified as excretory organs?

Human excretory organs include sweat glands, lungs, intestines, as well as the urinary system, which plays a major role in excretory processes.

3. Through which excretory organs are gaseous metabolic products eliminated?

Gaseous metabolic products (all carbon dioxide, methane and acetone taken in from outside ethanol and some others) and water (up to 500 ml per day) are removed through the lungs during breathing.

4. List the organs of the urinary system.

The urinary system consists of the kidneys, ureters, bladder and urethra.

5. Tell us about the structure of the kidney. What is its structural and functional unit?

Kidneys are paired bean-shaped organs located in abdominal cavity on either side of the spine. The length of the bud is 10-12 cm, width - 5-6 cm, weight - no more than 200 g. There are two layers in the bud. Darker - outer, cortical. The inner layer is lighter and wider - this is the medulla. The outside of the kidney is covered with a capsule, to which a layer of fatty tissue is adjacent to the outside. The cortex, in the form of columns, enters the medulla and divides it into 15-20 renal pyramids, the apices of which are directed into the kidney. From the top of each of the medulla pyramids, a urinary canaliculus extends into a small cavity inside the kidney - the renal pelvis, which collects urine. Adjacent to the renal pelvis, which continues in the form of a thin tube - the ureter, is the gate of the kidney, through which the renal artery enters and the renal vein and lymphatic capillaries. The structural and functional unit of the kidney is the nephron. There are up to 1 million of them in each kidney.

6. What is the structure and function of the nephron? Which of its structures are involved in the formation of primary urine, and which are involved in the formation of secondary urine?

The nephron begins with a thin-walled capsule, which, together with a glomerulus of blood capillaries, forms the renal corpuscle. The walls of the nephron capsule consist of epithelial cells that form the outer and inner plates, between which there is a cavity that passes into the thin nephron tubule. In the renal corpuscle, primary urine is formed by filtering blood plasma from the blood capillaries into the nephron capsules. The role of a biological filter is performed by the walls of capillaries and nephron capsules. Through these filters, water and all substances dissolved in it penetrate into the capsules from the blood flowing through the capillaries of the glomeruli, with the exception of blood cells and proteins that remain in the blood.

Filtration is very intensive. A person produces up to 7 liters of primary urine in 1 hour, i.e., up to 170 liters per day. During the day, up to 1,700 liters of blood passes through the kidneys. This means that from every 10 liters of blood, 1 liter of primary urine is formed.

Next, primary urine enters the nephron tubules, where water, many salts, amino acids, glucose and other substances are reabsorbed from it into the blood capillaries that encircle the tubules, which is the next stage of urine formation. Urea, uric acid and some other substances are not absorbed into the blood or are partially absorbed. Therefore, the concentration of urea in the resulting secondary urine increases tens of times. A person produces up to 1.5-2 liters of secondary urine per day.

The tubules of one nephron are 50-55 mm in length, and consist of first- and second-order nephron tubules and the loop of Henley between them. The tubule carrying secondary urine flows into the collecting duct, which flows into the small renal calyx. The small calyces become the large renal calyces, which empty into the renal pelvis.

7. What happens to primary urine during the process of reabsorption? How is it different from secondary?

See question 6.

8. How is the regulation of kidney function through the nervous and humoral pathways?

Nervous regulation: sympathetic influences lead to a decrease in the volume of urine produced due to the narrowing of the lumen of the afferent arterioles. Parasympathetic influences, increasing the passage of blood through the kidneys by narrowing the efferent arterioles, increase the formation of urine.

Humoral regulation: the hormone of the posterior lobe of the pituitary gland - vasopressin (second name: antidiuretic hormone, i.e. “anti-urinary” (diuresis - the amount of urine formed at a certain time)) increases the reabsorption of water and some substances in the convoluted tubules, reducing the volume of urine excreted . Adrenal hormones, adrenaline and aldosterone, also affect kidney function. Under the influence of adrenaline, urination decreases, aldosterone increases the reabsorption of sodium ions. Thyroid hormones and parathyroid glands can also indirectly affect the processes of urine formation by changing water-mineral metabolism in tissues. In addition, the kidneys themselves also secrete a hormone that regulates the processes of urine formation: angiotensin II narrows the lumens of the efferent arterioles of the glomeruli, increasing filtration in them.

9. Why are the kidneys often called a “biological filter”? Is this statement true?

This statement is true, the kidneys are the natural filter of our body. They divide substances that come to us through the bloodstream into those necessary for the body, which remain in the bloodstream or are reabsorbed, and into substances that need to be eliminated to maintain normal life. These are various toxic substances, breakdown products, as well as excess water in the bloodstream.

10. What gender differences exist in the structure of the human urinary system?

The urinary system in men and women differs in the length of the urinary canal: in men it is longer, as it passes through corpus spongiosum penis. Also, in men, the vas deferens open into the urethra; the urethra partially passes through the thickness of the prostate gland, which can cause difficulty urinating as the size of the gland increases. In women, urinary and reproductive system not so closely related. A shorter canal length causes more frequent inflammatory diseases urinary system in women (the smaller the canal, the easier it is for infection to enter the body and spread upward path to all organs of the system due to improper or insufficient personal hygiene).

11. What diseases of the urinary system do you know? Tell us about measures to prevent them.

Cystitis (inflammation of the bladder walls), pyelonephritis (inflammation collecting system kidneys), glomerulonephritis (inflammation of the glomeruli of the kidneys), urolithiasis disease(formation of stones in urinary tract, starting from the calyces of the kidneys, causing difficulty in the outflow of urine), good and malignant neoplasms, congenital pathologies(doubling, tripling of kidneys, fusion of kidneys, underdevelopment or absence of kidneys) and others.

Prevention of inflammatory kidney diseases will include: timely treatment of all foci of infection in the body, especially sore throats, caries (microorganisms that cause these diseases can enter the kidneys through the blood); avoiding hypothermia, taking care of maintaining immunity (hardening, taking vitamins, physical exercise); observing personal hygiene rules (washing warm water with soap 2 times a day); controlled medication intake (medicines are taken ONLY AS PRESCRIBED BY A DOCTOR, since many of them, if taken incorrectly, can provoke serious illnesses kidney); giving up alcohol, and spicy food containing excess spices and salt.

In the process of evolution, excretory products and the mechanisms of their removal from the body have changed greatly. With the complication of organization and the transition to new habitats, along with the skin and kidneys, other excretory organs appeared or the excretory function began to be performed secondarily by existing organs. Excretory processes in animals are associated with the activation of their metabolism, as well as much more complex processes life activity.

Protozoa are released by diffusion through the membrane. To remove excess water, protozoa have contractile vacuoles. Sponges and coelenterates— metabolic products are also removed by diffusion. The first excretory organs of the simplest structure appear in flatworms and nemerteans. They are called protonephridia, or flame cells. U annelids Each body segment has a pair of specialized excretory organs - metanephridia. Organs of excretion crustaceans are green glands located at the base of the antennae. Urine accumulates in the bladder and then comes out. U insects there are Malpighian tubules that open into digestive tract. The excretory system of all vertebrates is basically the same: it consists of renal corpuscles - nephrons, with the help of which metabolic products are removed from the blood. U birds and mammals in the process of evolution, a third type of kidney was developed - metanephros, the tubules of which have two highly convoluted sections (like in humans) and a long loop of Henle. In long sections of the renal tubule, water is reabsorbed, which allows animals to successfully adapt to life on land and use water sparingly.

Thus, in various groups of living organisms one can observe various organs secretions that adapt these organisms to their chosen habitat. Different structure excretory organs leads to differences in the quantity and type of metabolic products released. Most general products excretions for all organisms are ammonia, urea and uric acid. Not all metabolic products are excreted from the body. Many of them are useful and are part of the cells of this organism.

Pathways for excreting metabolic products

As a result of metabolism, simpler end products are formed: water, carbon dioxide, urea, uric acid, etc. they, as well as excess mineral salts, are removed from the body. Carbon dioxide and some water is excreted in the form of steam through the lungs. The main amount of water (about 2 liters) with urea, sodium chloride and other inorganic salts dissolved in it is excreted through the kidneys and in smaller quantities through the sweat glands of the skin. The liver also performs the excretion function to some extent. Salts heavy metals(copper, lead), which accidentally entered the intestines with food and are strong poisons, as well as rotting products are absorbed from the intestines into the blood and enter the liver. Here they are neutralized - they combine with organic substances, losing their toxicity and ability to be absorbed into the blood - and the final products of dissimilation are removed with bile through the intestines, lungs and skin, and the final products of dissimilation are removed from the body, harmful substances, excess water and inorganic substances and the constancy of the internal environment is maintained.

Excretory organs

Harmful breakdown products formed during the metabolic process (ammonia, uric acid, urea, etc.) must be removed from the body. This necessary condition vital activity, since their accumulation causes self-poisoning of the body and death. Many organs are involved in eliminating substances that the body does not need. All substances that are insoluble in water and, therefore, not absorbed in the intestine are excreted in the feces. Carbon dioxide and water (partially) are removed through the lungs, and water, salts, and some organic compounds are removed through sweat through the skin. However, most of the breakdown products are excreted in urine through the urinary system. In higher vertebrates and humans, the excretory system consists of two kidneys with their excretory ducts - the ureters, the bladder and the urethra, through which urine is excreted when the muscles of the bladder walls contract.

Kidneys - main body secretions, since the process of urine formation occurs in them.

The structure and function of the kidneys

Kidneys- paired bean-shaped organ - located on the inner surface back wall abdominal cavity at lumbar level. The renal arteries and nerves approach the kidneys, and the ureters and veins depart from them. The substance of the kidney consists of two layers: outer ( cortical) darker, and inner ( cerebral) light.

Brain matter It is represented by numerous convoluted tubules coming from the nephron capsules and returning to the renal cortex. The light inner layer consists of collecting tubes that form pyramids with their apices facing inward and ending with holes. By twisted renal tubules, densely braided capillaries, primary urine passes from the capsule. From primary urine, part of the water and glucose is returned (reabsorbed) to the capillaries. The remaining more concentrated secondary urine enters the pyramids.

Pelvis has the shape of a funnel, the wide side facing the pyramids, the narrow side facing the hilum of the kidney. Two large bowls adjoin it. Through the tubes of the pyramids, through the papillae, secondary urine seeps first into the small calyces (there are 8-9 of them), then into two large calyces, and from them into the renal pelvis, where it is collected and carried into the ureter.

Gate of the kidney- the concave side of the kidney from which the ureter arises. This is where the renal artery enters the kidney and where the renal vein exits. The ureter constantly drains secondary urine into the bladder. By renal artery blood is continuously brought in to be purified from waste products. After passing through vascular system kidney blood from the arterial becomes venous and is carried into the renal vein.

Ureters. Paired tubes are 30–35 cm long, composed of smooth muscle, lined with epithelium, and externally covered with connective tissue. The renal pelvis is connected to the bladder.

Bladder. A sac whose walls consist of smooth muscle lined with transitional epithelium. The bladder has an apex, body and bottom. In the fundus area, the ureters approach it at an acute angle. From the bottom - the neck - the urethra begins. The wall of the bladder consists of three layers: the mucous membrane, the muscular layer and the connective tissue membrane. The mucous membrane is lined with transitional epithelium, capable of folding and stretching. At the neck of the bladder there is a sphincter (muscle constrictor). The function of the bladder is to store urine and, when the walls contract, release urine out after (3 - 3.5 hours).

Urethra. A tube whose walls consist of smooth muscle lined with epithelium (stratified and columnar). There is a sphincter at the outlet of the canal. Removes urine to the external environment.

Each kidney consists of a huge number (about a million) of complex formations - nephrons. The nephron is the functional unit of the kidney. The capsules are located in the cortex of the kidney, while the tubules are located mainly in the medulla. The nephron capsule resembles a ball, top part which is pressed into the lower one, so that a gap is formed between its walls - the cavity of the capsule.

A thin and long convoluted tube extends from it - a tubule. The walls of the tubule, like each of the two walls of the capsule, are formed by a single layer of epithelial cells.

The renal artery, entering the kidney, divides into a large number of twigs. A thin vessel, called the transferring artery, enters the depressed part of the capsule, forming a ball of capillaries there. The capillaries are collected in a vessel that emerges from the capsule - the efferent artery. The latter approaches the convoluted tubule and again breaks up into capillaries that intertwine it. These capillaries form veins, which merge to form the renal vein and carry blood out of the kidney.

Nephrons

The structural and functional unit of the kidney is the nephron, which consists of a glomerular capsule, shaped like a double-walled glass, and tubules. Capsule covers the glomerular capillary network, resulting in the formation of a renal (Malpighian) corpuscle.

The glomerular capsule continues into proximal convoluted tubule. Followed by nephron loop, consisting of descending and ascending parts. The nephron loop passes into distal convoluted tubule, flowing into collecting duct. The collecting ducts continue into the papillary ducts. Throughout their entire length, the nephron tubules are surrounded by adjacent blood capillaries.

Urine formation

Urine is formed in the kidneys from blood, which the kidneys are well supplied with. Urine formation is based on two processes - filtration and reabsorption.

Filtration occurs in capsules. The diameter of the afferent artery is larger than that of the efferent artery, so the blood pressure in the capillaries of the glomerulus is quite high (70–80 mm Hg). thanks to this high blood pressure blood plasma, together with inorganic and organic substances dissolved in it, is pushed through the thin wall of the capillary and the inner wall of the capsule. In this case, all substances with a relatively small molecular diameter are filtered. Substances with large molecules (proteins), as well as blood cells, remain in the blood. Thus, as a result of filtration, primary urine, which includes all components of blood plasma (salts, amino acids, glucose and other substances) with the exception of proteins and fats. The concentration of these substances in primary urine is the same as in blood plasma.

The primary urine formed as a result of filtration in the capsules enters the tubules. As it passes through the tubules, the epithelial cells of their walls are taken back, returning a significant amount of water and substances necessary for the body to the blood. This process is called reabsorption. Unlike filtration, it occurs due to the active activity of tubular epithelial cells with energy consumption and oxygen absorption. Some substances (glucose, amino acids) are completely reabsorbed, so that secondary urine, which enters the bladder, they are not there. Other substances (mineral salts) are absorbed from the tubules into the blood in necessary for the body quantities, and the remaining amount is discharged outside.

Large total surface renal tubules(up to 40–50 m2) and active work their cells contribute to the fact that out of 150 liters of daily primary urine, only 1.5–2.0 liters are formed secondary(final). In an hour, a person produces up to 7200 ml of primary urine, and 60–120 ml of secondary urine is released. This means that 98–99% of it is absorbed back. Secondary urine differs from primary urine in the absence of sugar, amino acids and an increased concentration of urea (almost 70 times).

Continuously produced urine flows through the ureters into the bladder (urine reservoir), from which it is periodically removed from the body through the urethra.

Regulation of kidney activity

The activity of the kidneys, like the activity of other excretory systems, is regulated nervous system and glands internal secretion- mainly.

pituitary gland. Stopping kidney function inevitably leads to death resulting from poisoning of the body harmful products metabolism.

Kidney functions

The kidneys are the main excretory organ. They perform many different functions in the body.

Function
excretory	The kidneys remove excess water, organic and inorganic substances, and nitrogen metabolism products from the body.
Regulation of water balance	Allows you to control the volume of blood, lymph and intracellular fluid by changing the volume of water excreted in the urine.
Regulation of constancy osmotic pressure fluids (osmoregulation)	Occurs due to a change in the amount of osmotically active substances excreted.
Regulation of the ionic composition of liquids	It is caused by the possibility of selective changes in the intensity of excretion of various ions in the urine. It also affects the acid-base state through the excretion of hydrogen ions.
Formation and release of physiologically active substances into the bloodstream	Hormones, vitamins, enzymes.
Regulation	Regulation of blood pressure by changing the volume of blood circulating in the body.
Regulation of erythropoiesis	The released hormone erythropoietin affects the activity of division of red stem cells bone marrow, thereby changing the amount shaped elements (erythrocytes, platelets, leukocytes) in blood.
Formation of humoral factors	Blood clotting ( thromboblastine, thromboxane), as well as participation in the metabolism of the physiological anticoagulant heparin.
Metabolistic	They take part in the metabolism of proteins, lipids and carbohydrates.
Protective	They ensure the release of various toxic compounds from the body.

Excretion in plants

Plants, unlike animals, excrete only small amounts of nitrogenous products, which are excreted in the form of ammonia by diffusion. Aquatic plants release metabolic products by diffusion into environment. Land plants accumulate unnecessary substances (salts and organic substances - acids) in the leaves - and are released from them during leaf fall or accumulate them in stems and leaves, which die in the fall. Due to changes in turgor pressure in cells, plants can tolerate even significant shifts in the osmotic concentration of the surrounding fluid as long as it remains below the osmotic concentration inside the cells. If the concentration of dissolved substances in the surrounding fluid is higher than inside the cells, then plasmolysis and cell death occur.

The human excretory system is a set of organs that remove from our body excess water, toxic substances, end products of metabolism, and salts formed or entered into the body. We can say that the excretory system is a filter for the blood.

urinary system

This system consists of:

Two kidneys;

Bladder;

The ureter, which connects the kidney and bladder;

The urethra or urethra.

Functions of the human excretory system

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

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

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

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

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

6. The levels of phosphorus and calcium in the body are regulated.

The structure of the human excretory system

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

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

Urination

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

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

Urination

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

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

We can say that the human excretory system is represented by a collection of many organs that have a close connection with each other and complement each other’s work.