The genitourinary apparatus is represented in the body by excretory organs and reproductive organs.

The excretory organs consist of the kidneys and urinary tract. Kidneys (ren, nephros) are paired organs located retroperitoneally in the lumbar abdominal cavity. On the outside they are covered with fatty and fibrous capsules. The classification of the kidneys is based on the location of their embryonic lobules - the kidneys, each of which consists of the cortical (urinary), intermediate (vascular) and medulla (urinary) zones. The definitive kidney also has these same zones. At the large cattle the buds are grooved, in omnivores they are smooth multipapillary, in single-hoofed animals, carnivores and small ruminants they are smooth unipapillary. The structural and functional unit of the kidney is the nephron, which consists of a vascular glomerulus surrounded by a capsule (the glomerulus and capsule form the Malpighian corpuscle, located in the cortical zone), a system of convoluted and straight tubules (straight tubules form the loop of Henle, located in the medulla). The medulla has renal pyramids that end in a papilla, and the papilla, in turn, opens into the renal pelvis (Fig.).

Rice. Kidney structure: a - cattle: 1 - renal artery; 2 - renal vein; 3 - fibrous capsule; 4 - cortex; 5- medulla and renal papillae; 6-pedicles of the ureter; 7- kidney cups; 8- ureter; b, c - horses: 1 - renal arteries; 2 - renal veins; 3- ureters; 4- renal recessus; 5 - fibrous capsule; 6 - cortex; 7 - pelvis; 8 - medulla

The renal pelvis is absent only in cattle. The kidneys in the body perform the following functions: remove products of protein metabolism from the body, maintain water-salt balance and glucose levels, regulate blood pH and maintain constant osmotic pressure, remove substances from the body that have entered from the outside (Fig.).

Rice. Topography of pig kidneys: 1 - fatty capsule of the kidneys; 2 - left kidney; 3 - transverse costal process; 4 - vertebral body; 5 - vertebral muscles; 6 - right kidney; 7 - caudal vena cava; 8 - abdominal aorta; 9 - left renal artery; 10 - serous membrane of the kidney

Urine is formed in two phases: filtration and reabsorption. The first phase is ensured by special conditions of blood supply in the renal glomeruli. The result of this phase is the formation of primary urine (blood plasma without proteins). From every 10 liters of blood flowing through the glomeruli, 1 liter of primary urine is formed. During the second phase, reabsorption of water, many salts, glucose, amino acids, etc. occurs. In addition to reabsorption, active secretion occurs in the kidney tubules. As a result, secondary urine is formed. From every 90 liters of primary urine passing through the tubules, 1 liter of secondary urine is formed. The activity of the kidneys is regulated by the autonomic nervous system and the cerebral cortex (nervous regulation), as well as by the hormones of the pituitary gland, thyroid gland and adrenal glands (humoral regulation).

The urinary tract includes the renal calyces and renal pelvis, ureters, bladder and urethra. The ureter lies behind the peritoneum and consists of three parts: abdominal, pelvic and vesical. It opens in the area of ​​the bladder neck between its mucous and muscular membranes. The bladder (vesica urinaria) is located on the pubic bones (in carnivores and omnivores, mostly in the abdominal cavity) and consists of an apex, which is directed into the abdominal cavity, a body and a neck, which is directed into the pelvic cavity and has a sphincter (Fig.).

Rice. The stallion's genitourinary apparatus: 1 - right kidney; 2 - caudal vena cava; 3 - abdominal aorta; 4 - left kidney; 5 - left ureter; 6 - rectovesical recess; 7 - bladder; 8 - bulbous gland; 9 - seed tube; 10 - vessels of the testis; 11 - body of the penis; 12 - opening of the vaginal canal; 13 - external levator of the testis; 14 - common vaginal tunica; 15 - prepuce; 16- glans penis; 17- urogenital process; 18- testicular vessels; 19- peritoneum; 20 - ventral ligament of the bladder; 21 - apex of the bladder; 22 - lateral ligaments of the bladder; 23 - rectum

The bladder has a well-developed muscular layer, which has three layers of muscle. The bladder is held in its position by three ligaments: two lateral and one median. The urethra (urethra) has significant sexual characteristics. So, in females it is long and located under the vagina. In males, it is short, since it almost immediately merges with the genital ducts and is called the urogenital canal, which has a considerable length and opens on the head of the penis with the urogenital (urethral) process.

The reproductive organs of males and females, despite the apparent differences, have a common schematic diagram structures and consist of gonads, excretory tracts and external genitalia (auxiliary apparatus). During their development, the excretory tracts are closely connected with the ducts of the primary kidney.

The sex glands in males are called testes (testis, didymis, orchis), and in females - ovaries (ovarium, oopharon). In females, the gonads are located in the abdominal cavity behind the kidneys (in cattle at the level of the sacral tuberosities) and do not have their own excretory ducts (the egg enters directly into the abdominal cavity). The activity of the ovaries is cyclical. In males, the gonads are located in a special outgrowth of the abdominal cavity - the testicular sac (lies between the thighs or under the anus), and have their own excretory ducts(straight tubules of the testis). The activity of the testes is non-cyclical (Fig.).

Rice. Structure of the testes: a - stallion: 1 - testis; 2 - head of the appendage; 3 - pampiniform plexus; 4 - testicular vein; 5- testicular artery; 6 - seed tube; 7- spermatic cord; 8 - sinus of the appendage; 9 - body of the appendage; 10 - appendage edge; 11 - tail appendage; 12 - caudate end; 13 - capitate end; b - bull: 1 - testis; 2 - head of the appendage; 3 - shell of the pampiniform appendage; 4- testicular vein; 5 - testicular artery; 6 - seed wire; 7- spermatic cord; 8- pampiniform plexus; 9 - sinus of the appendage; 10 - body of the appendage; 11 - tail appendage; c - boar: 1 - testis; 2 - head of the appendage; 3 - testicular vein; 4 - testicular artery; 5 - seed tube; 6 - spermatic cord; 7 - pampiniform plexus; 8 - sinus of the appendage; 9 - body of the appendage; 10 - tail appendage

The excretory tracts in females include: oviducts, uterus, vagina and genitourinary vestibule. The oviduct (oviductus, salpinx, tubae uterina, tubae fallopii) is the fertilization organ. It consists of a funnel (the initial part), an ampulla (the middle convoluted part in which fertilization occurs) and an isthmus (the final part). The uterus (uterus, metra, hystera) is the organ of fruiting, the vagina (vagina) is the organ of copulation, the genitourinary vestibule (vestibulum vaginae) is the organ where the reproductive and urinary tracts unite. The uterus consists of two horns, a body and a cervix in bicornuate-type domestic animals, located mostly in the abdominal cavity (the place of fruiting), a body and a cervix with a smooth muscle sphincter (located in the pelvic cavity and has a cervical canal). The wall of the uterus consists of three layers: mucous (endometrium) - internal, muscular (myometrium) - middle, serous (perimetry) - external.

In males, the excretory ducts include: straight tubules of the testis, epididymis, vas deferens and urogenital canal. The epididymis (epididymis) is located on the testis and is covered with a common serous membrane (a special vaginal membrane). It has a head, body and tail. The vas deferens (ductus deferens) begins from the tail of the epididymis and, as part of the spermatic cord, enters the abdominal cavity, runs dorsally from the bladder and passes into the genitourinary canal. The urogenital canal has two parts: the pelvic (located at the bottom of the pelvic cavity) and the oud (located on the ventral surface of the penis). The initial part of the pelvic part is called the prostate part (Fig.).

Rice. Urogenital canal of male domestic animals: 1 - ischium; 2 - ilium; 3 - bladder; 4 - ureter; 5 - seed tube; 6- ampoule of the vas deferens; 7- vesicular glands; 8 - body of the prostate; 9 - pelvic part of the genitourinary canal; 10 - bulbous glands; 11 - penis retractor; 12 - bulb of the genitourinary canal; 13 - ischiocavernosus muscle, ischial bulbous muscle

The accessory sex glands are associated with the excretory ducts in males and females. In females these are vestibular glands located in the wall of the genitourinary vestibule, and in males these are prostate, or prostate (located in the neck of the bladder), vesicular glands (located on the side of the bladder, absent in males) and bulbous (bulbourethral) glands (located at the transition of the pelvic part of the genitourinary canal into the audible, absent in males). All accessory sex glands of males open into the pelvic part of the urogenital canal. All organs of the reproductive system of males and females, located in the abdominal cavity, have their own mesentery (Fig.).

Rice. Cow genitourinary apparatus: 1 - lateral ligaments of the bladder; 2 - bladder; 3 - oviduct; 4, 9 - wide uterine ligament; 5 - rectum; 6 - ovary and funnel of the oviduct; 7 - interhorn ligament; 8 - uterine horns; 10 - ventral ligament of the bladder

Rice. Genitourinary apparatus of the mare: 1 - left oviduct; 2 - left horn of the uterus; 3 - ovarian bursa; 4 - right kidney; 5- caudal vena cava; 6 - abdominal aorta; 7- left kidney; 8, 12 - wide uterine ligament; 9 - left ureter; 10 - rectum; 11 - rectal-uterine cavity; 13 - bladder; 14 - lateral ligaments of the bladder; 15 - ventral ligament of the bladder; 16 - vesico-uterine recess; 17 - left horn of the uterus; 18 - peritoneum

The external genital organs in females are called the vulva and are represented by the labia (pudenda) and the clitoris, which originates from the ischial tuberosities, and its head is located in the ventral commissure of the lips. In males, the external genital organs include the penis (penis), which also originates from the ischial tuberosities and consists of two legs, a body and a head, covered by the prepuce (a fold of skin consisting of two leaves), and the testicular sac, its outer layer called the scrotum. In addition to the scrotum, the testicular sac includes the tunica vaginalis (derived from the peritoneum and transverse abdominal fascia) and the levator testis muscle (derived from the internal oblique abdominal muscle).

Reproduction(reproduction) is a biological process that ensures the preservation of a species and an increase in its population. It is associated with puberty (the beginning of the functioning of the reproductive organs, increased secretion of sex hormones and the appearance of sexual reflexes).

Pairing- a complex reflex process, manifested in the form of sexual reflexes: approach, hugging reflex, erection, copulatory reflex, ejaculation. The centers of sexual reflexes are located in the lumbar and sacral parts of the spinal cord, and their manifestation is influenced by the cerebral cortex and hypothalamus. The hypothalamus also regulates the reproductive cycle in females.

Sexual cycle- a complex of physiological and morphological changes occurring in the body of females from one estrus (or heat) to another.

2.1 Kidney examination

Cattle have kidneys of the grooved or multipapillary type. On rectal palpation, individual lobules are felt. In pigs, the kidneys are smooth, multipapillary; in horses, small cattle, deer, dogs, and cats, they are almost smooth. The topography of the kidneys in animals of different species has its own characteristics.

When examining the kidneys, the animal is examined, palpation and percussion of the kidneys, radiological and functional studies are carried out. Laboratory testing of urine is of particular importance.

Inspection. Kidney damage is accompanied by depression and immobility of animals. Diarrhea, hypotension and atony of the forestomach are possible; in carnivores - vomiting and convulsions. With chronic kidney diseases, exhaustion, itching, baldness, and dull coat occur. Small white scales of urea appear on the surface of the skin. Of particular importance is the appearance of renal (“flying”) edema. Dropsy of the serous cavities may occur. With nephrotic edema, hypoproteinemia occurs (up to 55 g/l and below).

Nephrotic edema occurs when the endothelium of the capillaries is desquamated, when fluid leaks into the tissue in large quantities. The cause of such edema may be increased blood pressure.

Edema in acute renal failure occurs against the background of uremia.

PalpaqiI allows you to determine the position, shape, size, mobility, consistency, tuberosity and sensitivity of the kidneys during external and rectal examination.

In cattle, external (with low fatness) and internal palpation are carried out. Externally, in adult animals, only the right kidney can be examined in the right hungry fossa under the ends of the transverse processes of the 1st-3rd lumbar vertebrae. Internal palpation is performed rectally. The left kidney is located under the 3rd-5th lumbar vertebrae, mobile, hanging 10-12 cm from the spine. In small cows, you can palpate the caudal edge of the right kidney, which is located under the transverse processes of the vertebrae from the last intercostal space to the 2nd-3rd lumbar on the right. It is well fixed on the short mesentery; unlike the left kidney, it almost does not move during palpation.

In horses, only internal palpation of the kidneys is possible. The left kidney extends from the last rib to the transverse process of the 3rd-4th lumbar vertebrae. In large horses it is possible to feel only the caudal edge of the left kidney. In small animals, the medial and lateral surfaces of the kidneys, the renal pelvis and the renal artery can be palpated (by pulsation).

In pigs, external palpation of the kidneys is possible only in emaciated individuals. The kidneys are located under the transverse processes of the 1st-4th lumbar vertebrae.

In sheep and goats, the kidneys are accessible to deep palpation through the abdominal wall. The left kidney is located under the transverse processes of the 4th-6th lumbar vertebrae, and the right kidney is located under the 1st-3rd. Their surface is smooth. They move little during palpation.

In small animals, the kidneys are palpated through the abdominal wall. The left kidney is located in the anterior left corner of the hungry fossa, under the 2nd-4th lumbar vertebrae. The right kidney can only be partially palpated; under the 1st-3rd lumbar vertebrae it is possible to feel its caudal edge.

Enlarged kidneys can be caused by paranephritis, pyelonephritis, hydronephrosis, nephrosis, amyloidosis. Reduction of the kidneys is noted in chronic processes - chronic nephritis and pyelonephritis, cirrhosis. Changes in the surface of the kidneys (lumpyness) may be a consequence of tuberculosis, echinococcosis, leukemia, tumor, abscess, chronic lesions (nephritis, pyelonephritis). Kidney pain is noted with glomerulo-, pyelo- and paranephritis, as well as with urolithiasis. When sharp, gentle blows are applied to the kidney area, pain occurs.

Percussion. In large animals, the kidneys are percussed using a hammer and pleximeter, in small animals - digitally. Kidneys in healthy animals cannot be detected by percussion, since they are not adjacent to the abdominal wall. In sick animals with a sharp enlargement of the kidneys (paranephritis, pyelonephritis, hydronephrosis), this method can establish a dull sound at the location of the kidneys.

For large animals, the beating method is used: the palm of the left hand is pressed to the lower back in the area of ​​​​the projection of the kidneys, and short, gentle blows are applied with the fist of the right hand.

In healthy animals, no signs of pain are detected during beating; pain is noted in the case of paranephritis, inflammation of the kidneys and renal pelvis, and urolithiasis.

Biopsy. This method is rarely used for diagnostic purposes. A piece of kidney tissue is removed through the skin using a special needle and syringe or trocar for soft tissue biopsy. The abdominal wall is pierced from the side of the right or left hungry fossa, at the site of the projection of the kidneys. The biopsy is examined histologically to establish morphological changes, sometimes using the bacteriological method to determine the microflora in the kidney tissue.

X-ray examination is of great importance in small animals for detecting stones and tumors in the urinary system, cysticity, hydronephrosis, nephritis, edema. An increase in the shadow of only one kidney is possible with hydronephrosis or the presence of a tumor.

Functional studies kidney tests are reduced to determining in the blood substances secreted by the kidneys (residual nitrogen, uric acid, creatinine, etc.), the ability of the kidneys to concentrate and dilute urine, studying the excretory function of the kidneys after exercise, as well as the cleansing function (clearance) of the kidneys.

Functional studies. They include determining the amount of urine excreted and its relative density; a test with indigo carmine (modified by K.K. Movsum-Zadeh) is also used.

Zimnitsky test: the animal is kept on a normal diet for 1 day, the water supply is not limited. Urine samples are collected into a urine bag during natural urination, the amount of urine, its relative density, and sodium chloride content are determined. The wider the boundaries of the controlled parameters, the better the kidney function is preserved. In cattle, the normal total diuresis in relation to the water drunk is 23.1%, the chloride content is 0.475%. With functional renal failure, nocturnal diuresis (nocturia) predominates, and with significant failure, a decrease in the relative density of urine is noted - hyposthenuria, often combined with polyuria.

Water load test: the animal is given tap water at room temperature through a nasopharyngeal tube in the morning on an empty stomach after emptying the bladder. The dose of water for cows is 75 ml per 1 kg of animal weight. After 4 hours, the animal is given dry food, usually included in the diet. Water is excluded from the diet until the next day. During the test, urine is collected into a urine bag and its quantity and relative density are determined.

In healthy cows, urination becomes more frequent, the relative density of urine decreases (1.002...1.003), within 4...6 hours from the start of the experiment, 33...60.9% of the water introduced inside for the purpose of loading is excreted, and for the rest of the time days - 10...23%. Total diuresis is 48.5...76.7%. An increase in water excretion by the kidneys during water load in sick animals reflects tubular failure, and water retention in the body reflects glomerular failure.

Concentration test: the animal is kept without water for 24 hours. Urine is collected during voluntary urination and its relative density is determined. Normally, in cattle, on the day the experiment begins, a decrease in urination is noted up to 1...4 times, diuresis decreases to 1...4 liters, and the relative density of urine increases by 8...19 divisions. With tubular failure in the kidneys, deviations in the studied parameters are noted.

Test with indigo carmine: 5...6 hours before the injection of indigo carmine, the animal is deprived of water. A special fixed catheter is inserted into the bladder, through which several milliliters of urine are taken into a test tube for control. After this, the cow is infused intravenously with a 4% solution of indigo carmine at a dose of 20 ml and urine samples are taken through a catheter, first after 5 minutes, and then at intervals of 15 minutes.

In healthy cows, indigo carmine begins to be excreted by the kidneys after 5...I minutes. The coloring of urine becomes more intense in the interval from 20 minutes to 1 hour 30 minutes. After 1 hour 58 minutes to 4 hours from the start of the experiment, traces of indigo carmine were detected in the urine. The release of the dye is impaired when there is a disorder of kidney function, renal blood flow, or urine outflow from the renal pelvis and ureters.

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The structure of the kidneys of mammals

KIDNEYS | Encyclopedia Around the World

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• HUMAN ANATOMY
• METABOLIC DISORDERS
• UROLOGY

KIDNEYS, the main excretory (removing end products of metabolism) organ of vertebrates. Invertebrates, such as the snail, also have organs that perform a similar excretory function and are sometimes called kidneys, but they differ from the kidneys of vertebrates in structure and evolutionary origin.

Function.

The main function of the kidneys is to remove water and metabolic end products from the body. In mammals, the most important of these products is urea, the main final nitrogen-containing product of protein breakdown (protein metabolism). In birds and reptiles, the main end product of protein metabolism is uric acid, an insoluble substance that appears as a white mass in excrement. In humans, uric acid is also formed and excreted by the kidneys (its salts are called urates).

The human kidneys excrete about 1–1.5 liters of urine per day, although this amount can vary greatly. The kidneys respond to increased water intake by increasing the production of more dilute urine, thereby maintaining normal body water levels. If water intake is limited, the kidneys help conserve water in the body by using as little water as possible to make urine. The volume of urine may decrease to 300 ml per day, and the concentration of excreted products will be correspondingly higher. Urine volume is regulated by antidiuretic hormone (ADH), also called vasopressin. This hormone is secreted by the posterior pituitary gland (a gland located at the base of the brain). If the body needs to conserve water, ADH secretion increases and urine volume decreases. On the contrary, when there is excess water in the body, ADH is not released and the daily volume of urine can reach 20 liters. Urine output, however, does not exceed 1 liter per hour.

Structure.

Mammals have two kidneys located in the abdomen on either side of the spine. The total weight of two kidneys in a person is about 300 g, or 0.5–1% of body weight. Despite their small size, the kidneys have an abundant blood supply. Within 1 minute, about 1 liter of blood passes through the renal artery and exits back through the renal vein. Thus, in 5 minutes, a volume of blood equal to the total amount of blood in the body (about 5 liters) passes through the kidneys to remove metabolic products.

The kidney is covered with a connective tissue capsule and a serous membrane. A longitudinal section of the kidney shows that it is divided into two parts, called the cortex and medulla. Most of the substance of the kidney consists of a huge number of very thin convoluted tubes called nephrons. Each kidney contains more than 1 million nephrons. Their total length in both kidneys is approximately 120 km. The kidneys are responsible for producing the fluid that eventually becomes urine. The structure of the nephron is the key to understanding its function. At one end of each nephron there is an extension - a round formation called the Malpighian body. It consists of a two-layer, so-called. Bowman's capsule, which encloses the network of capillaries that form the glomerulus. The rest of the nephron is divided into three parts. The coiled part closest to the glomerulus is the proximal convoluted tubule. Next is a thin-walled straight section, which, turning sharply, forms a loop, the so-called. loop of Henle; it distinguishes (sequentially): descending section, bend, ascending section. The coiled third part is the distal convoluted tubule, which flows together with other distal tubules into the collecting duct. From the collecting ducts, urine enters the renal pelvis (actually the expanded end of the ureter) and then along the ureter into the bladder. Urine is discharged from the bladder through the urethra at regular intervals. The cortex contains all the glomeruli and all the convoluted parts of the proximal and distal tubules. The medulla contains the loops of Henle and the collecting ducts located between them.

Urine formation.

In the glomerulus, water and substances dissolved in it leave the blood through the walls of the capillaries under the influence of blood pressure. The pores of the capillaries are so small that they trap blood cells and proteins. Consequently, the glomerulus acts as a filter that allows fluid to pass through without proteins, but with all the substances dissolved in it. This fluid is called ultrafiltrate, glomerular filtrate, or primary urine; it is processed as it passes through the rest of the nephron.

In the human kidney, the volume of ultrafiltrate is about 130 ml per minute or 8 liters per hour. Since a person's total blood volume is approximately 5 liters, it is obvious that most of the ultrafiltrate must be absorbed back into the blood. Assuming that the body produces 1 ml of urine per minute, then the remaining 129 ml (more than 99%) of water from the ultrafiltrate must be returned to the bloodstream before it becomes urine and is excreted from the body.

Ultrafiltrate contains many valuable substances (salts, glucose, amino acids, vitamins, etc.) that the body cannot lose in significant quantities. Most are reabsorbed as the filtrate passes through the proximal tubule of the nephron. Glucose, for example, is reabsorbed until it completely disappears from the filtrate, i.e. until its concentration approaches zero. Since the transport of glucose back into the blood, where its concentration is higher, goes against the concentration gradient, the process requires additional energy and is called active transport.

As a result of the reabsorption of glucose and salts from the ultrafiltrate, the concentration of substances dissolved in it decreases. The blood turns out to be a more concentrated solution than the filtrate, and “attracts” water from the tubules, i.e. water passively follows actively transported salts (see OSMOSIS). This is called passive transport. With the help of active and passive transport, 7/8 of the water and substances dissolved in it are absorbed back from the contents of the proximal tubules, and the rate of decrease in the volume of the filtrate reaches 1 liter per hour. Now the intracanalicular fluid contains mainly “waste”, such as urea, but the process of urine formation is not yet complete.

The next segment, the loop of Henle, is responsible for creating very high concentrations of salts and urea in the filtrate. In the ascending limb of the loop, active transport of dissolved substances, primarily salts, occurs into the surrounding tissue fluid of the medulla, where as a result a high concentration of salts is created; due to this, from the descending bend of the loop (permeable to water), part of the water is sucked out and immediately enters the capillaries, while the salts gradually diffuse into it, reaching their highest concentration in the bend of the loop. This mechanism is called countercurrent concentrating mechanism. The filtrate then enters the distal tubules, where other substances can pass into it due to active transport.

Finally, the filtrate enters the collecting ducts. Here it is determined how much liquid will be additionally removed from the filtrate, and therefore what the final volume of urine will be, i.e. volume of final, or secondary, urine. This stage is regulated by the presence or absence of ADH in the blood. The collecting ducts are located between the numerous loops of Henle and run parallel to them. Under the influence of ADH, their walls become permeable to water. Because the concentration of salts in the loop of Henle is so high and water tends to follow the salts, it is actually drawn out of the collecting ducts, leaving a solution with a high concentration of salts, urea, and other solutes. This solution is the final urine. If there is no ADH in the blood, then the collecting ducts remain poorly permeable to water, water does not come out of them, the volume of urine remains large and it turns out to be diluted.

Animal kidneys.

The ability to concentrate urine is especially important for animals where access to urine is difficult. drinking water. The kangaroo rat, for example, living in the desert of the southwestern United States, produces urine 4 times more concentrated than that of a human. This means that the kangaroo rat is capable of removing toxins in very high concentrations using a minimal amount of water.

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KIDNEYS

Kidney - gene (nephros) - a paired organ of dense consistency of red-brown color. The kidneys are built like branched glands and are located in the lumbar region.

The kidneys are quite large organs, approximately the same on the right and left, but not the same in animals of different species (Table 10). Young animals have relatively large kidneys.

The kidneys are characterized by a bean-shaped, somewhat flattened shape. There are dorsal and ventral surfaces, convex lateral and concave medial edges, cranial and caudal ends. Near the middle of the medial edge, vessels and nerves enter the kidney and the ureter emerges. This place is called the renal hilum.

10. Kidney mass in animals

Rice. 269. Urinary organs of cattle (from the ventral surface)

The outside of the kidney is covered with a fibrous capsule that connects to the kidney parenchyma. The fibrous capsule is surrounded externally by a fatty capsule, and on the ventral surface it is also covered with a serous membrane. The kidney is located between the lumbar muscles and the parietal layer of the peritoneum, i.e. retroperitoneally.

The kidneys are supplied with blood through the large renal arteries, which receive up to 15-30% of the blood pushed into the aorta by the left ventricle of the heart. Innervated by the vagus and sympathetic nerves.

In cattle (Fig. 269), the right kidney is located in the area from the 12th rib to the 2nd lumbar vertebra, with its cranial end touching the liver. Its caudal end is wider and thicker than the cranial one. The left kidney hangs on a short mesentery behind the right one at the level of the 2-5th lumbar vertebrae; when the scar is filled, it moves slightly to the right.

On the surface, the kidneys of cattle are divided by grooves into lobules, of which there are up to 20 or more (Fig. 270, a, b). The grooved structure of the kidneys is the result of incomplete fusion of their lobules during embryogenesis. On the section of each lobule, the cortical, medullary and intermediate zones are distinguished.

The cortical, or urinary, zone (Fig. 271, 7) is dark red in color and located superficially. It consists of microscopic renal corpuscles arranged radially and separated by stripes of the medullary rays.

The medullary or urinary drainage zone of the lobule is lighter, radially striated, located in the center of the kidney, and is shaped like a pyramid. The base of the pyramid faces outwards; From here the brain rays exit into the cortical zone. The apex of the pyramid forms the renal papilla. The medullary zone of adjacent lobules is not divided by grooves.

Between the cortical and medullary zones, an intermediate zone is located in the form of a dark strip. In it, arcuate arteries are visible, from which radial interlobular arteries are separated into the cortical zone. Along the latter there are renal corpuscles. Each body consists of a glomerulus - a glomerulus and a capsule.

The vascular glomerulus is formed by the capillaries of the afferent artery, and the two-layer capsule surrounding it is formed by special excretory tissue. The efferent artery emerges from the choroid glomerulus. It forms a capillary network on a convoluted tubule, which starts from the glomerular capsule. The renal corpuscles with convoluted tubules make up the cortical zone. In the region of the medullary rays, the convoluted tubule becomes the straight tubule. The set of straight tubules forms the basis of the medulla. Merging with each other, they form papillary ducts, which open at the apex of the papilla and form a ethmoidal field. The renal corpuscle, together with the convoluted tubule and its vessels, constitute the structural and functional unit of the kidney - the nephron. In the renal corpuscle of the nephron, liquid - primary urine - is filtered from the blood of the vascular glomerulus into the cavity of its capsule. During the passage of primary urine through the convoluted tubule of the nephron, most (up to 99%) water and some substances that cannot be removed from the body, such as sugar, are absorbed back into the blood. This explains the large number and length of nephrons. Thus, a person has up to 2 million nephrons in one kidney.

Buds that have superficial grooves and many papillae are classified as grooved multipapillary. Each papilla is surrounded by a renal calyx (see Fig. 270). Secondary urine secreted into the calyces passes through short stalks into two urinary ducts, which connect to form the ureter.

Rice. 270. Kidneys

Rice. 271. Structure of the renal lobule

Rice. 272. Topography of the kidneys (from the ventral surface)

In a pig, the kidneys are bean-shaped, long, flattened dorsoventrally, and belong to the smooth multipapillary type (see Fig. 270, c, d). They are characterized by complete fusion of the cortical zone, with a smooth surface. However, the section shows 10-16 renal pyramids. They are separated by cords of cortical substance - renal columns. Each of the 10-12 renal papillae (some papillae merge with each other) is surrounded by a renal calyx, which opens into a well-developed renal cavity - the pelvis. The wall of the pelvis is formed by mucous, muscular and adventitial membranes. The ureter begins from the pelvis. The right and left kidneys lie under the 1-3 lumbar vertebrae (Fig. 272), the right kidney does not come into contact with the liver. Smooth multipapillary buds are also characteristic of humans.

The horse's right kidney is heart-shaped, and the left kidney is bean-shaped, smooth on the surface. The section shows complete fusion of the cortex and medulla, including the papillae. The cranial and caudal parts of the renal pelvis are narrowed and are called the renal ducts. There are 10-12 renal pyramids. Such buds belong to the smooth single-papillary type. The right kidney extends cranially to the 16th rib and enters the renal depression of the liver, and caudally to the first lumbar vertebra. The left kidney lies in the area from the 18th thoracic to the 3rd lumbar vertebra.

The dog's kidneys are also smooth, single-papillary (see Fig. 270, e, f), of a typical bean-shaped shape, located under the first three lumbar vertebrae. In addition to horses and dogs, smooth single-papillary buds are characteristic of small ruminants, deer, cats, and rabbits.

In addition to the three types of kidneys described, some mammals (polar bear, dolphin) have multiple kidneys of a grape-shaped structure. Their embryonic lobules remain completely separated throughout the animal's life and are called buds. Each kidney is built according to overall plan a normal kidney, on a section it has three zones, a papilla and a calyx. The kidneys are connected to each other by excretory tubes that open into the ureter.

After the birth of an animal, the growth and development of the kidneys continues, which can be seen, in particular, in the example of the kidneys of calves. During the first year of extrauterine life, the mass of both kidneys increases almost 5 times. The kidneys grow especially intensively during the milk period after birth. At the same time, the microscopic structures of the kidneys also change. For example, the total volume of the renal corpuscles increases by 5 times during the year, and by 15 times by the age of six, the convoluted tubules lengthen, etc. At the same time, the relative mass of the kidneys decreases by half: from 0.51% in newborn calves to 0. 25% in yearlings (according to V.K. Birikh and G.M. Udovin, 1972). The number of renal lobules remains virtually constant after birth.

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Internal structure of mammals Mammalian organ systems

Compared to other amniotes, the mammalian digestive system is characterized by significant complexity. This is manifested in an increase in the total length of the intestine, its clear differentiation into sections and increased function of the digestive glands.

The structural features of the system in different species are largely determined by the type of nutrition, among which herbivory and mixed type of nutrition predominate. Eating exclusively animal food is less common and is characteristic mainly of predators. Plant foods are used by terrestrial, aquatic and underground mammals. The type of nutrition of mammals determines not only the specific structure of animals, but also in many ways their way of existence and their system of behavior.

Terrestrial inhabitants use various types of plants and their parts - stems, leaves, branches, underground organs (roots, rhizomes). Typical “vegetarians” include ungulates, proboscis, lagomorphs, rodents and many other animals.

Among herbivorous animals, specialization in food consumption is often observed. Many ungulates (giraffes, deer, antelopes), proboscideans (elephants) and a number of others feed mainly on the leaves or twigs of trees. The juicy fruits of tropical plants form the basis of nutrition for many tree inhabitants.

The wood is used by beavers. The food supply for mice, squirrels, and chipmunks consists of a variety of seeds and fruits of plants, from which reserves are made for the wintering period. There are many species that feed mainly on grasses (ungulates, marmots, gophers). The roots and rhizomes of plants are consumed by underground species - jerboas, zokor, mole rats and mole rats. The diet of manatees and dugongs consists of aquatic grasses. There are animals that feed on nectar (certain species of bats, marsupials).

Carnivores have a wide range of species that make up their food supply. Invertebrates (worms, insects, their larvae, mollusks, etc.) occupy a significant place in the diet of many animals. Insectivorous mammals include hedgehogs, moles, shrews, bats, anteaters, pangolins and many others. Insects are often eaten by herbivorous species (mice, gophers, squirrels) and even quite large predators (bears).

Among aquatic and semi-aquatic animals there are piscivores (dolphins, seals) and zooplankton feeders (baleen whales). A special group of carnivorous species consists of predators (wolves, bears, felines, etc.) that hunt large animals, either alone or in a pack. There are species that specialize in feeding on the blood of mammals (vampire bats). Carnivores often consume plant foods - seeds, berries, nuts. These animals include bears, martens, and canines.

The digestive system of mammals begins with the vestibule of the mouth, which is located between the fleshy lips, cheeks and jaws. In some animals it is expanded and is used to temporarily reserve food (hamsters, gophers, chipmunks). The oral cavity contains a fleshy tongue and heterodont teeth sitting in the alveoli. The tongue serves as an organ of taste, participates in the capture of food (anteaters, ungulates) and in chewing it.

Most animals are characterized by a complex dental system, which includes incisors, canines, premolars and molars. The number and ratio of teeth varies among species with different types of nutrition. Thus, the total number of teeth in a mouse is 16, a hare - 28, a cat - 30, a wolf - 42, a wild boar - 44, and a marsupial opossum - 50.

To describe the dental system of different types, a dental formula is used, the numerator of which reflects the number of teeth in half upper jaw, and the denominator is the lower jaw. For ease of recording, the letter designations of different teeth are accepted: incisors - i (incisive), canines - c (canini), premolars - pm (praemolares), molars - m (molares). Predatory animals have well-developed canines and molars with cutting edges, while herbivores (ungulates, rodents) have predominantly strong incisors, which is reflected in the corresponding formulas. For example, the dental formula of a fox looks like this: (42). The dental system of a hare is represented by the formula: (28), and of a boar: . (44)

The dental system of a number of species is not differentiated (pinnipeds and toothed whales) or is weakly expressed (in many insectivorous species). Some animals have a diastema - a space on the jaws devoid of teeth. It arose evolutionarily as a result of a partial reduction of the dental system. The diastema of most herbivores (ruminants, lagomorphs) was formed due to the reduction of the canines, part of the premolar teeth, and sometimes the incisors.

The formation of a diastema in predatory animals is associated with an enlargement of the fangs. The teeth of most mammals are replaced once during ontogenesis (diphyodont dental system). In many herbivorous species, teeth are capable of constant growth and self-sharpening as they wear (rodents, rabbits).

The ducts of the salivary glands open into the oral cavity, the secretion of which is involved in wetting food, contains enzymes for breaking down starch and has an antibacterial effect.

Through the pharynx and esophagus, food passes into the well-demarcated stomach, which has different volume and structure. The walls of the stomach have numerous glands that secrete hydrochloric acid and enzymes (pepsin, lipase, etc.). In most mammals, the stomach has a retort-shaped stomach and two sections - cardiac and pyloric. In the cardial (initial) part of the stomach, the environment is more acidic than in the pyloric part.

The stomach of monotremes (echidna, platypus) is characterized by the absence of digestive glands. In ruminants, the stomach has a more complex structure - it consists of four sections (rumen, mesh, book and abomasum). The first three sections make up the “forestomach,” the walls of which are lined with stratified epithelium without digestive glands. It is intended only for fermentation processes to which the absorbed herbal mass is exposed under the influence of symbiont microbes. This process takes place in an alkaline environment of three sections. The partially fermented mass is regurgitated portionwise into the mouth. Chewing it thoroughly (chewing gum) helps to enhance the fermentation process when food re-enters the stomach. Gastric digestion is completed in the rennet, which has an acidic environment.

The intestine is long and clearly divided into three sections - thin, thick and straight. The total length of the intestine varies significantly depending on the feeding pattern of the animal. For example, its length exceeds the body size in bats by 1.5–4 times, in rodents by 5–12 times, and in sheep by 26 times. At the border of the small and large intestines there is a cecum, intended for the fermentation process, so it is especially well developed in herbivorous animals.

In the first loop small intestine – duodenum The ducts of the liver and pancreas enter. The digestive glands not only secrete enzymes, but also actively participate in metabolism, excretory functions and hormonal regulation of processes.

The digestive glands also have the walls of the small intestine, so the process of digestion of food continues in it and absorption occurs nutrients into the bloodstream. In the thick section, thanks to fermentation processes, difficult-to-digest food is processed. The rectum serves to form excrement and reabsorb water.

Respiratory organs and gas exchange.

The main gas exchange in mammals is determined by pulmonary respiration. To a lesser extent, it occurs through the skin (approximately 1% of total gas exchange) and the mucous membrane of the respiratory tract. Lungs of alveolar type. The mechanism of thoracic breathing is due to the contraction of the intercostal muscles and the movement of the diaphragm - a special muscle layer separating the thoracic and abdominal cavities.

Through the external nostrils, air enters the vestibule of the nasal cavity, where it is warmed and partially cleared of dust, thanks to the mucous membrane with ciliated epithelium. Nasal cavity includes the respiratory and olfactory sections. In the respiratory section, further purification of the air from dust and disinfection occurs due to bactericidal substances secreted by the mucous membrane of its walls. This section has a well-developed capillary network, ensuring a partial supply of oxygen to the blood. The olfactory region contains outgrowths of the walls, due to which a labyrinth of cavities is formed, increasing the surface for capturing odors.

Through the choanae and pharynx, air passes into the larynx, supported by a system of cartilage. In front are unpaired cartilages - the thyroid (characteristic only for mammals) with the epiglottis and cricoid. The epiglottis covers the entrance to Airways when swallowing food. At the back of the larynx lie the arytenoid cartilages. Between them and the thyroid cartilage are the vocal cords and vocal muscles, which determine the production of sounds. Cartilaginous rings also support the trachea, which follows the larynx.

Two bronchi originate from the trachea, which enter the spongy tissue of the lungs with the formation of numerous small branches (bronchioles), ending in alveolar vesicles. Their walls are densely permeated with blood capillaries that ensure gas exchange. The total area of ​​the alveolar vesicles significantly (50–100 times) exceeds the body surface, especially in animals with a high degree of mobility and level of gas exchange. An increase in the respiratory surface is also observed in mountain species constantly experiencing oxygen deficiency.

The respiratory rate is largely determined by the size of the animal, the intensity metabolic processes and motor activity. The smaller the mammal, the relatively higher the heat loss from the body surface and the more intense the level of metabolism and oxygen demand. The most energy-intensive animals are small species, due to which they feed almost constantly (shrews, shrews). During the day they consume 5–10 times more feed than their own biomass.

Ambient temperature has a significant influence on breathing rate. An increase in summer temperature by 10° leads to an increase in the respiratory rate of predatory species (fox, polar bear, black bear) by 1.5–2 times.

The respiratory system plays a significant role in maintaining temperature homeostasis. Along with exhaled air, a certain amount of water (“polypnoe”) and thermal energy are removed from the body. The higher the summer temperature, the more often the animals breathe and the higher the “polypnoe” indicators. Thanks to this, animals manage to avoid overheating of the body.

The circulatory system of mammals is basically similar to that of birds: the heart is four-chambered, lies in the pericardial sac (pericardium); two circles of blood circulation; complete separation of arterial and venous blood.

The systemic circulation begins with the left aortic arch, emerging from the left ventricle, and ends with the vena cava, returning venous blood to the right atrium.

The unpaired innominate artery (Fig. 73) originates from the left aortic arch, from which the right subclavian and paired carotid arteries depart. Each carotid artery, in turn, is divided into two arteries - the external and internal carotid arteries. The left subclavian artery arises directly from the aortic arch. Having circled the heart, the aortic arch stretches along the spine in the form of the dorsal aorta. Large arteries depart from it, supplying blood to internal systems and organs, muscles and limbs - splanchnic, renal, iliac, femoral and caudal.

Venous blood from the body organs is collected through a number of vessels (Fig. 74), from which the blood drains into the common vena cava, carrying blood to the right atrium. From the front of the body it runs through the anterior vena cava, which takes blood from the jugular veins of the head and the subclavian veins, which extend from the forelimbs. On each side of the neck there are two jugular vessels - the external and internal veins, which merge with the corresponding subclavian vein, forming the vena cava.

Many mammals exhibit asymmetrical development of the anterior vena cava. The innominate vein flows into the right anterior vena cava, formed by the confluence of the veins on the left side of the neck - the left subclavian and jugular. It is also typical for mammals to preserve rudiments of the posterior cardinal veins, which are called azygos (vertebral) veins. An asymmetry can also be traced in their development: the left azygos vein connects with the right azygos vein, which flows into the right anterior vena cava.

From the back of the body, venous blood returns through the posterior vena cava. It is formed by the fusion of vessels extending from the organs and hind limbs. The largest of venous vessels, forming the posterior vena cava - azygos caudal, paired femoral, iliac, renal, genital and a number of others. The posterior vena cava passes, without branching, through the liver, penetrates the diaphragm and carries venous blood into the right atrium.

Gate system The liver is formed by one vessel - the portal vein of the liver, which arises as a result of the confluence of veins coming from the internal organs.

These include: the splenogastric vein, anterior and posterior mesenteric veins. Portal vein forms complex system capillaries that penetrate the liver tissue, which at the exit unite again and form short hepatic veins that flow into the posterior vena cava. The renal portal system in mammals is completely reduced.

The pulmonary circulation originates from the right ventricle, where venous blood from the right atrium enters, and ends at the left atrium. From the right ventricle, venous blood exits through the pulmonary artery, which splits into two vessels leading to the lungs. Blood oxidized in the lungs enters the left atrium through paired pulmonary veins.

The heart varies in size among different species of mammals. Small and active animals have a relatively larger heart. The same pattern can be observed in relation to the heart rate. Thus, the pulse rate of a mouse is 600 per minute, that of a dog is 140, and that of an elephant is 24.

Hematopoiesis occurs in different organs mammals. Red blood cells (erythrocytes), granulocytes (neutrophils, eosinophils and basophils) and platelets are produced by the bone marrow. Red blood cells are anucleate, which increases their transfer of oxygen to organs and tissues, without wasting it on their own respiration processes. Lymphocytes are formed in the spleen, thymus and lymph nodes. The reticuloendothelial system produces cells of the monocytic series.

Excretory system.

IN water-salt metabolism in mammals, it is mainly carried out by the kidneys, the work of which is coordinated by pituitary hormones. A certain proportion of water-salt exchange is performed skin, equipped with sweat glands, and intestines.

The kidneys of mammals, like all amniotes, are of the metanephridial type (pelvic). The main excretion product is urea. The kidneys are bean-shaped, suspended from the dorsal side on the mesentery. The ureters depart from them, flowing into the bladder, the ducts of which open in males on the copulatory organ, and in females - in the vestibule of the vagina.

Mammalian kidneys have a complex structure and are characterized by a high filtering function.

The outer (cortical) layer is a system of glomeruli, consisting of Bowman's capsules with glomeruli of blood vessels (Malpighian corpuscles). Filtration of metabolic products occurs from the blood vessels of the Malpighian corpuscles into Bowman's capsules. The primary filtrate in its content is blood plasma, devoid of proteins, but containing many substances useful to the body.

An efferent tubule (nephron) arises from each Bowman's capsule. It has four sections - the proximal convoluted, loop of Henle, distal convoluted and collecting duct. The nephron system forms lobules (pyramids) in the medulla of the kidneys, clearly visible on a macro section of the organ.

In the upper (proximal) section, the nephron makes several bends that are intertwined with blood capillaries. It reabsorbs (reabsorbs) water and other beneficial substances into the blood - sugars, amino acids and salts.

In the following sections (loop of Henle, distal convoluted) further absorption of water and salts occurs. As a result of the complex filtering work of the kidney, the final metabolic product is formed - secondary urine, which flows through the collecting ducts into the renal pelvis, and from it into the ureter. The reabsorption activity of the kidneys is enormous: up to 180 liters of water per day pass through the human renal tubules, while only about 1–2 liters of secondary urine are formed.

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Kidney physiology

The kidneys play an exceptional role in the normal functioning of the body. By removing decay products, excess water, salts, harmful substances and some medications, the kidneys thereby perform an excretory function.

In addition to the excretory function, the kidneys also have others, no less important functions. By removing excess water and salts from the body, mainly sodium chloride, the kidneys thereby maintain osmotic pressure internal environment body. Thus, the kidneys take part in water-salt metabolism and osmoregulation.

The kidneys, along with other mechanisms, ensure the constancy of the reaction (pH) of the blood by changing the intensity of the release of acidic or alkaline salts of phosphoric acid when the blood pH shifts to the acidic or alkaline side.

The kidneys are involved in the formation (synthesis) of certain substances, which they subsequently remove. The kidneys also perform a secretory function. They have the ability to secrete organic acids and bases, K+ and H+ ions. This ability of the kidneys to secrete various substances plays a significant role in the implementation of their excretory function. And finally, the role of the kidneys has been established not only in mineral, but also in lipid, protein and carbohydrate metabolism.

Thus, the kidneys, regulating osmotic pressure in the body, the constancy of the blood reaction, carrying out synthetic, secretory and excretory functions, take an active part in maintaining the constancy of the composition of the internal environment of the body (homeostasis).

The structure of the kidneys. In order to more clearly understand the work of the kidneys, it is necessary to become familiar with their structure, since the functional activity of the organ is closely related to its structural features. The kidneys are located on both sides of the lumbar spine. On their inner side there is a depression in which there are vessels and nerves surrounded by connective tissue. The kidneys are covered with a connective tissue capsule. The size of an adult human kidney is about 11 × 10-2 × 5 × 10-2 m (11 × 5 cm), weight on average 0.2-0.25 kg (200-250 g).

On a longitudinal section of the kidney, two layers are visible: the cortex is dark red and the medulla is lighter (Fig. 39).

Rice. 39. Structure of the kidney. A - general structure; B - a section of renal tissue enlarged several times; 1 - Shumlyansky capsule; 2 - convoluted tubule of the first order; 3 - loop of Henle; 4 - convoluted tubule of the second order

A microscopic examination of the structure of mammalian kidneys shows that they consist of a large number of complex formations - the so-called nephrons. The nephron is the functional unit of the kidney. The number of nephrons varies depending on the type of animal. In humans, the total number of nephrons in the kidney reaches an average of 1 million.

The nephron is a long tubule, the initial section of which, in the form of a double-walled bowl, surrounds the arterial capillary glomerulus, and the final section flows into the collecting duct.

The following sections are distinguished in the nephron: 1) the Malpighian corpuscle consists of the Shumlyansky vascular glomerulus and the surrounding Bowman’s capsule (Fig. 40); 2) the proximal segment includes the proximal convoluted and straight tubules; 3) the thin segment consists of thin ascending and descending limbs of the loop of Henle; 4) the distal segment is composed of the thick ascending limb of the loop of Henle, the distal convoluted and communicating tubules. The excretory duct of the latter flows into the collecting duct.

Rice. 40. Scheme of the Malpighian glomerulus. 1 - bringing vessel; 2 - efferent vessel; 3 - capillaries of the glomerulus; 4 - capsule cavity; 5 - convoluted tubule; 6 - capsule

Different segments of the nephron are located in specific areas of the kidney. The cortical layer contains vascular glomeruli, elements of the proximal and distal segments urinary tubules. The medulla contains elements of the thin segment of the tubules, thick ascending limbs of the loops of Henle and collecting ducts (Fig. 41).

Rice. 41. Diagram of the structure of the nephron (according to Smith). 1 - glomerulus; 2 - proximal convoluted tubule; 3 - descending part of the loop of Henle; 4 - ascending part of the loop of Henle; 5 - distal convoluted tubule; 6 - collecting tube. In circles - the structure of the epithelium in various parts of the nephron

The collecting ducts, merging, form common excretory ducts, which pass through the medulla of the kidney to the tips of the papillae, protruding into the cavity of the renal pelvis. The renal pelvis opens into the ureters, which in turn empty into the bladder.

Blood supply to the kidneys. The kidneys receive blood from the renal artery, which is one of the large branches of the aorta. The artery in the kidney is divided into a large number of small vessels - arterioles, bringing blood to the glomerulus (afferent arteriole a), which then break up into capillaries (the first network of capillaries). The capillaries of the vascular glomerulus, merging, form an efferent arteriole, the diameter of which is 2 times less than the diameter of the afferent arteriole. The efferent arteriole again breaks up into a network of capillaries intertwining the tubules (the second network of capillaries).

Thus, the kidneys are characterized by the presence of two networks of capillaries: 1) capillaries of the vascular glomerulus; 2) capillaries intertwining the renal tubules.

Arterial capillaries turn into venous capillaries, which later, merging into veins, give blood to the inferior vena cava.

The blood pressure in the capillaries of the glomerulus is higher than in all capillaries of the body. It is equal to 9.332-11.299 kPa (70-90 mm Hg), which is 60-70% of the pressure in the aorta. In the capillaries entwining the kidney tubules, the pressure is low - 2.67-5.33 kPa (20-40 mm Hg).

All blood (5-6 l) passes through the kidneys in 5 minutes. During the day, about 1000-1500 liters of blood flows through the kidneys. Such abundant blood flow allows you to completely remove all substances that are unnecessary and even harmful to the body.

The lymphatic vessels of the kidneys accompany the blood vessels, forming a plexus at the porta renal, surrounding the renal artery and vein.

Innervation of the kidneys. In terms of the wealth of innervation, the kidneys occupy second place after the adrenal glands. Efferent innervation is carried out mainly by sympathetic nerves.

Parasympathetic innervation of the kidneys is slightly expressed. A receptor apparatus is found in the kidneys, from which afferent (sensitive) fibers depart, running mainly as part of the splanchnic nerves.

A large number of receptors and nerve fibers are found in the capsule surrounding the kidneys. Excitation of these receptors can cause pain.

Recently, the study of the innervation of the kidneys has attracted Special attention due to the problem of their transplantation.

Juxtaglomerular apparatus. The juxtaglomerular, or periglomerular, apparatus (JGA) consists of two main elements: myoepithelial cells, located mainly in the form of a cuff around the afferent arteriole of the glomerulus, and cells of the so-called macula densa of the distal convoluted tubule.

JGA is involved in the regulation of water-salt homeostasis and maintaining constant blood pressure. JGA cells secrete a biologically active substance - renin. The secretion of renin is inversely related to the amount of blood flowing through the afferent arteriole and to the amount of sodium in the primary urine. With a decrease in the amount of blood flowing to the kidneys and a decrease in the amount of sodium salts in it, the release of renin and its activity increase.

In the blood, renin interacts with the plasma protein hypertensinogen. Under the influence of renin, this protein passes into its active form - hypertensin (angiotonin). Angiotonin has a vasoconstrictor effect, due to which it is a regulator of renal and general blood circulation. In addition, angiotonin stimulates the secretion of the hormone of the adrenal cortex - aldosterone, which is involved in the regulation of water-salt metabolism.

In a healthy body, only small amounts of hypertensin are produced. It is destroyed by a special enzyme (hypertensinase). In some kidney diseases, the secretion of renin increases, which can lead to a persistent increase in blood pressure and disruption of water-salt metabolism in the body.

Mechanisms of urine formation

Urine is formed from blood plasma flowing through the kidneys and is a complex product of the activity of nephrons.

Currently, urine formation is considered as a complex process consisting of two stages: filtration (ultrafiltration) and reabsorption (reabsorption).

Glomerular ultrafiltration. In the capillaries of the Malpighian glomeruli, water with all inorganic and organic substances of low molecular weight dissolved in it is filtered from the blood plasma. This fluid enters the glomerular capsule (Bowman's capsule), and from there into the renal tubules. By chemical composition it is similar to blood plasma, but contains almost no proteins. The resulting glomerular filtrate is called primary urine.

In 1924, the American scientist Richards obtained direct evidence in experiments on animals glomerular filtration. He used microphysiological research methods in his work. In frogs, guinea pigs and the rats, Richards exposed the kidney and inserted a thin micropipette into one of Bowman’s capsules with a microscope, with the help of which he collected the resulting filtrate. An analysis of the composition of this liquid showed that the content of inorganic and organic substances (with the exception of protein) in the blood plasma and primary urine is exactly the same.

The filtration process is facilitated by high blood pressure (hydrostatic) in the capillaries of the glomeruli - 9.33-12.0 kPa (70-90 mm Hg).

The higher hydrostatic pressure in the capillaries of the glomeruli compared with the pressure in the capillaries of other areas of the body is due to the fact that the renal artery arises from the aorta, and the afferent arteriole of the glomerulus is wider than the efferent arteriole. However, the plasma in the glomerular capillaries is not filtered under all this pressure. Blood proteins retain water and thereby prevent urine from filtering. The pressure created by plasma proteins (oncotic pressure) is 3.33-4.00 kPa (25-30 mmHg). In addition, the filtration force is also reduced by the pressure of the liquid located in the cavity of Bowman's capsule, which is 1.33-2.00 kPa (10-15 mm Hg).

Thus, the pressure under the influence of which the filtration of primary urine is carried out is equal to the difference between the blood pressure in the capillaries of the glomeruli, on the one hand, and the sum of the pressure of blood plasma proteins and the pressure of the fluid located in the cavity of Bowman’s capsule, on the other. Therefore, the filtration pressure value is 9.33-(3.33+2.00)=4.0 kPa. Urine filtration stops if blood pressure is below 4.0 kPa (30 mmHg) (critical value).

A change in the lumen of the afferent and efferent vessels causes either an increase in filtration (narrowing of the efferent vessel) or its decrease (narrowing of the afferent vessel). The amount of filtration is also affected by changes in the permeability of the membrane through which filtration occurs. The membrane includes the endothelium of the glomerular capillaries, the main (basal) membrane and the cells of the inner layer of Bowman's capsule.

Tubular reabsorption. In the renal tubules, reabsorption (reabsorption) of water, glucose/part of the salts and a small amount of urea from primary urine into the blood occurs. As a result of this process, final, or secondary, urine is formed, which in its composition differs sharply from the primary. It does not contain glucose, amino acids, or some salts and the concentration of urea is sharply increased (Table 11).

Table 11. Contents of certain substances in blood plasma and urine

During the day, 150-180 liters of primary urine are formed in the kidneys. Due to the reabsorption of water and many dissolved substances in the tubules, the kidneys excrete only 1-1.5 liters of final urine per day.

Reabsorption can occur actively or passively. Active reabsorption is carried out due to the activity of the epithelium of the renal tubules with the participation of special enzyme systems with energy consumption. Glucose, amino acids, phosphates, and sodium salts are actively reabsorbed. These substances are completely absorbed in the tubules and are absent in the final urine. Due to active reabsorption, reabsorption of substances from urine into the blood is possible even when their concentration in the blood is equal to the concentration in the tubular fluid or higher.

Passive reabsorption occurs without energy consumption due to diffusion and osmosis. A major role in this process belongs to the difference in oncotic and hydrostatic pressure in the capillaries of the tubules. Due to passive reabsorption, water, chlorides, and urea are reabsorbed. The removed substances pass through the wall of the tubules only when their concentration in the lumen reaches a certain threshold value. Substances that are to be eliminated from the body undergo passive reabsorption. They are always found in urine. The most important substance in this group is the final product of nitrogen metabolism - urea, which is reabsorbed in small quantities.

The reabsorption of substances from urine into the blood varies in different parts of the nephron. Thus, in the proximal part of the tubule, glucose, partially sodium and potassium ions are absorbed, in the distal part - sodium chloride, potassium and other substances. Throughout the entire tubule, water is absorbed, and in its distal part it is 2 times more than in the proximal part. The loop of Henle occupies a special place in the mechanism of reabsorption of water and sodium ions due to the so-called rotary-countercurrent system. Let's consider its essence. The loop of Henle has two branches: descending and ascending. The epithelium of the descending limb allows water to pass through, and the epithelium of the ascending limb is not permeable to water, but is capable of actively absorbing sodium ions and transferring them into the tissue fluid, and through it back into the blood (Fig. 42).

Rice. 42. Scheme of operation of the rotary-counterflow system (according to Best and Taylor). The darkened background shows the concentration of urine and tissue fluid. White arrows - release of water, black arrows - sodium ions; 1 - convoluted tubule, passing into the proximal part of the loop; 2 - convoluted tubule emerging from the distal part of the loop; 3 - collecting tube

Passing through descending department loops of Henle, urine releases water, thickens, and becomes more concentrated. The release of water occurs passively due to the fact that at the same time active reabsorption of sodium ions occurs in the ascending section. Entering the tissue fluid, sodium ions increase the osmotic pressure in it and thereby contribute to the attraction of water from the descending limb into the tissue fluid. In turn, an increase in urine concentration in the loop of Henle due to the reabsorption of water facilitates the transition of sodium ions from urine into tissue fluid. Thus, in the loop of Henle, large amounts of water and sodium ions are reabsorbed.

In the distal convoluted tubules, further absorption of sodium, potassium, water and other substances occurs. Unlike the proximal convoluted tubules and the loop of Henle, where the reabsorption of sodium and potassium ions does not depend on their concentration (obligatory reabsorption), the amount of reabsorption of these ions in the distal tubules is variable and depends on their level in the blood (facultative reabsorption). Consequently, the distal sections of the convoluted tubules regulate and maintain the constant concentration of sodium and potassium ions in the body.

In addition to reabsorption, the process of secretion occurs in the tubules. With the participation of special enzyme systems, active transport of certain substances from the blood into the lumen of the tubules occurs. Of the products of protein metabolism, creatinine and para-aminohippuric acid undergo active secretion. This process manifests itself in full force when substances foreign to it are introduced into the body.

Thus, active transport systems function in the renal tubules, especially in their proximal segments. Depending on the state of the body, these systems can change the direction of active transfer of substances, i.e., they provide either their secretion (excretion) or reverse absorption.

In addition to carrying out filtration, reabsorption and secretion, renal tubular cells are capable of synthesizing certain substances from various organic and inorganic products. Thus, hippuric acid (from benzoic acid and glycocol) and ammonia (by deamination of some amino acids) are synthesized in the cells of the renal tubules. The synthetic activity of the tubules is also carried out with the participation of enzyme systems.

Function of collecting ducts. Further absorption of water occurs in the collecting ducts. This is facilitated by the fact that the collecting ducts pass through the medulla of the kidney, in which the tissue fluid has a high osmotic pressure and therefore attracts water.

Thus, urine formation is a complex process in which, along with the phenomena of filtration and reabsorption, the processes of active secretion and synthesis play an important role. If the filtration process occurs mainly due to energy blood pressure, i.e. ultimately due to the functioning of cardio-vascular system, then the processes of reabsorption, secretion and synthesis are the result of the active activity of tubular cells and require energy expenditure. This is associated with the kidneys' greater need for oxygen. They use 6-7 times more oxygen than muscles (per unit mass).

Regulation of kidney activity

Regulation of kidney activity is carried out by neurohumoral mechanisms.

Nervous regulation. It has now been established that the autonomic nervous system regulates not only the processes of glomerular filtration (by changing the lumen of blood vessels), but also tubular reabsorption.

The sympathetic nerves innervating the kidneys are mainly vasoconstrictor. When they are irritated, the excretion of water decreases and the excretion of sodium in the urine increases. This is due to the fact that the amount of blood flowing to the kidneys decreases, the pressure in the glomeruli drops, and, consequently, the filtration of primary urine decreases. Transection of the celiac nerve leads to increased urine output from the denervated kidney.

Parasympathetic (vagus) nerves act on the kidneys in two ways: 1) indirectly, by changing the activity of the heart, they cause a decrease in the strength and frequency of heart contractions, as a result of which blood pressure decreases and the intensity of diuresis changes; 2) regulating the lumen of the kidney vessels.

With painful stimulation, diuresis reflexively decreases until it stops completely (painful anuria). This is due to the fact that narrowing occurs renal vessels due to stimulation of the sympathetic nervous system and an increase in the secretion of the pituitary hormone - vasopressin.

The nervous system has a trophic effect on the kidneys. Unilateral denervation of the kidney is not accompanied by significant difficulties in its functioning. Bilateral transection of nerves causes disruption of metabolic processes in the kidneys and a sharp decrease in their functional activity. A denervated kidney cannot quickly and subtly rearrange its activity and adapt to changes in the level of water-salt load. After introducing 1 liter of water into the animal's stomach, an increase in diuresis in the denervated kidney occurs later than in a healthy one.

In the laboratory of K. M. Bykov, through the development of conditioned reflexes, a pronounced influence of the higher parts of the central nervous system on the functioning of the kidneys was shown. It has been established that the cerebral cortex causes changes in the functioning of the kidneys either directly through the autonomic nerves or through the pituitary gland, changing the release of vasopressin into the bloodstream.

Humoral regulation is carried out mainly by the hormones vasopressin (antidiuretic hormone) and aldosterone.

The posterior pituitary hormone vasopressin increases the permeability of the wall of the distal convoluted tubules and collecting ducts for water and thereby promotes its reabsorption, which leads to a decrease in urine output and an increase in the osmotic concentration of urine. With an excess of vasopressin, a complete cessation of urine formation (anuria) may occur. The lack of this hormone in the blood leads to the development serious illness- diabetes insipidus. With this disease, a large amount of light-colored urine with a low relative density, which lacks sugar, is released.

Aldosterone (hormone of the adrenal cortex) promotes the reabsorption of sodium ions and the excretion of potassium ions in the distal portions of the tubules and inhibits the reabsorption of calcium and magnesium in their proximal portions.

Quantity, composition and properties of urine

A person excretes on average about 1.5 liters of urine per day, but this amount is not constant. For example, diuresis increases after drinking heavily and consuming protein, the breakdown products of which stimulate urine formation. On the contrary, urine formation decreases with the consumption of small amounts of water, protein, and with increased sweating, when a significant amount of liquid is excreted through sweat.

The intensity of urine formation fluctuates throughout the day. More urine is produced during the day than at night. A decrease in urine formation at night is associated with a decrease in the body’s activity during sleep, with a slight drop in blood pressure. Night urine is darker and more concentrated.

Physical activity has a pronounced effect on urine formation. With prolonged work, there is a decrease in urine excretion from the body. This is explained by the fact that with increased physical activity, blood flows in greater quantities to the working muscles, as a result of which the blood supply to the kidneys decreases and urine filtration decreases. At the same time, physical activity is usually accompanied by increased sweating, which also helps to reduce diuresis.

Urine color. Urine is a clear, light yellow liquid. When it settles in the urine, a sediment forms, which consists of salts and mucus.

Urine reaction. Urine reaction healthy person predominantly slightly acidic, its pH ranges from 4.5 to 8.0. The reaction of urine may vary depending on nutrition. When eating mixed food (animal and plant origin) human urine has a slightly acidic reaction. When eating primarily meat and other protein-rich foods, the urine reaction becomes acidic; plant foods contribute to the transition of the urine reaction to neutral or even alkaline.

Relative density of urine. The density of urine is on average 1.015-1.020 and depends on the amount of fluid taken.

Composition of urine. The kidneys are the main organ for removing nitrogenous products of protein breakdown from the body - urea, uric acid, ammonia, purine bases, creatinine, indican.

Urea is the main product of protein breakdown. Up to 90% of all urine nitrogen comes from urea. In normal urine, protein is absent or only traces of it are detected (no more than 0.03% o). The appearance of protein in the urine (proteinuria) usually indicates kidney disease. However, in some cases, namely during intense muscular work (long-distance running), protein may appear in the urine of a healthy person due to a temporary increase in the permeability of the membrane of the choroidal glomerulus of the kidneys.

Among the organic compounds of non-protein origin in the urine there are: salts of oxalic acid, which enter the body with food, especially plant foods; lactic acid released after muscle activity; ketone bodies formed when the body converts fats into sugar.

Glucose appears in the urine only in cases when its content in the blood is sharply increased (hyperglycemia). The excretion of sugar in the urine is called glucosuria.

The appearance of red blood cells in the urine (hematuria) is observed in diseases of the kidneys and urinary organs.

The urine of a healthy person and animals contains pigments (urobilin, urochrome), on which it depends. yellow. These pigments are formed from bilirubin in bile in the intestines and kidneys and are secreted by them.

A large amount of inorganic salts is excreted in the urine - about 15·10-3-25·10-3 kg (15-25 g) per day. Sodium chloride, potassium chloride, sulfates and phosphates are excreted from the body. The acidic reaction of urine also depends on them (Table 12).

Table 12. Amount of substances included in urine (excreted in 24 hours)

Excretion of urine. The final urine flows from the tubules into the pelvis and from it into the ureter. The movement of urine through the ureters into the bladder is carried out under the influence of gravity, as well as due to the peristaltic movements of the ureters. The ureters, entering the bladder obliquely, form a kind of valve at its base that prevents the reverse flow of urine from the bladder.

Urine accumulates in the bladder and is periodically removed from the body through the act of urination.

The bladder contains so-called sphincters, or sphincters (ring-shaped muscle bundles). They tightly close the outlet of the bladder. The first of the sphincters - the sphincter of the bladder - is located at its exit. The second sphincter - the urethral sphincter - is located slightly lower than the first and closes the urethra.

The bladder is innervated by parasympathetic (pelvic) and sympathetic nerve fibers. Excitation of sympathetic nerve fibers leads to increased peristalsis of the ureters, relaxation of the muscular wall of the bladder (detrusor) and increased tone of its sphincters. Thus, stimulation of the sympathetic nerves promotes the accumulation of urine in the bladder. When parasympathetic fibers are stimulated, the wall of the bladder contracts, the sphincters relax and urine is expelled from the bladder.

Urine continuously flows into the bladder, which leads to increased pressure in it. An increase in pressure in the bladder to 1.177-1.471 Pa (12-15 cm water column) causes the need to urinate. After urination, the pressure in the bladder decreases to almost 0.

Urination is a complex reflex act consisting of simultaneous contraction of the bladder wall and relaxation of its sphincters. As a result, urine is expelled from the bladder.

An increase in pressure in the bladder leads to the emergence of nerve impulses in the mechanoreceptors of this organ. Afferent impulses enter spinal cord to the center of urination (II-IV segments of the sacral region). From the center, along the efferent parasympathetic (pelvic) nerves, impulses go to the detrusor and sphincter of the bladder. A reflex contraction of its muscle wall and relaxation of the sphincter occurs. At the same time, from the center of urination, excitation is transmitted to the cerebral cortex, where a feeling of the urge to urinate occurs. Impulses from the cerebral cortex travel through the spinal cord to the urethral sphincter. The act of urination begins. Cortical control manifests itself in delaying, intensifying, or even voluntarily inducing urination. In young children, cortical control of urinary retention is absent. It is produced gradually with age.

The kidneys are paired organs of dense consistency, red-brown in color, smooth, covered on the outside with three membranes: fibrous, fatty, serous. They are bean-shaped and located in the abdominal cavity. The kidneys are located retroperitoneally, i.e. between the psoas muscles and the parietal layer of the peritoneum. The right kidney (except in pigs) borders the caudate process of the liver, leaving a renal depression on it. udder vegetative pituitary gland trophoblast

Structure. Outside, the kidney is surrounded by a fatty capsule, and on the ventral surface it is also covered with a serous membrane - the peritoneum. The inner edge of the kidneys, as a rule, is strongly concave, and represents the portal of the kidney - the place where vessels, nerves and the exit of the ureter enter the kidney. In the depths of the hilum there is a renal cavity, and the renal pelvis is located in it. The kidney is covered with a dense fibrous capsule, which is loosely connected to the renal parenchyma. Near the middle of the inner layer, vessels and nerves enter the organ and the ureter emerges. This place is called the renal hilum. On the section of each kidney, the cortical, or urinary, cerebral, or urinary, and intermediate zones, where the arteries are located, are distinguished. The cortical (or urinary) zone is located on the periphery and is dark red in color; On the cut surface, renal corpuscles are visible in the form of points located radially. The rows of corpuscles are separated from each other by stripes of the medullary rays. The cortical zone protrudes into the medullary zone between the pyramids of the latter; in the cortical zone, the products of nitrogen metabolism are separated from the blood, i.e. urine formation. In the cortical layer there are renal corpuscles, consisting of a glomerulus - a glomerulus (vascular glomerulus), formed by the capillaries of the afferent artery, and a capsule, and in the medulla - convoluted tubules. The initial section of each nephron is a vascular glomerulus surrounded by the Shumlyansky-Bowman capsule. The glomerulus of capillaries (Malpighian glomerulus) is formed by the afferent vessel - the arteriole, which breaks up into many (up to 50) capillary loops, which then merge in the efferent vessel. A long convoluted tubule begins from the capsule, which in the cortical layer has a highly convoluted shape - the proximal convoluted tubule of the first order, and straightening, it passes into the medulla, where it makes a bend (loop of Henle) and returns to the cortex, where it convolutes again, forming the distal convoluted tubule second order tubule. After this, they flow into the collecting duct, which serves as a collector for many tubules.

Cattle kidneys. Topography: right in the area from the 12th rib to the 2-3rd lumbar vertebra, and left - in the area of ​​the 2-5th lumbar vertebra.

In cattle, the weight of the kidneys reaches 1-1.4 kg. Type of kidneys in cattle: grooved multipapillary - individual kidneys are fused with their central sections. On the surface of such a bud, lobules separated by grooves are clearly visible; The section shows numerous passages, and the latter already form a common ureter.

Horse kidneys. The right kidney is heart-shaped and located between the 16th rib and the 1st lumbar vertebra, and the left kidney, bean-shaped, is located between the 18th thoracic and 3rd lumbar vertebrae. Depending on the type of feeding, an adult horse excretes 3-6 liters (maximum 10 liters) of slightly alkaline urine per day. Urine is a clear, straw-yellow liquid. If it is colored intense yellow or Brown color, this indicates any health problems.

Type of kidney in a horse: smooth single-papillary kidneys, characterized by complete fusion of not only the cortical, but also the medullary zones - they have only one common papilla, immersed in the renal pelvis.

The urinary system includes the kidneys, ureters, bladder, urethra, urogenital sinus (in females) or genitourinary canal (in males). The urinary organs produce, temporarily store and excrete from the body liquid end products of metabolism - urine. Perform an excretory function, extracting from the blood and removing from the body harmful products nitrogen metabolism (urea, uric acid, ammonia, creatine, creatinine), foreign substances (paints, drugs, etc.), some hormones (prolan, androsterone, etc.). By removing excess water, minerals and acidic foods, the kidneys regulate water-salt metabolism and maintain relative constancy of osmotic pressure and active blood reaction. The kidneys synthesize hormones (renin, angiotensin) that are involved in the regulation of blood pressure and diuresis (urination).

Brief data on the development of the urinary system

In the most primitively organized multicellular animals (hydra), the excretory function is carried out diffusely over the entire surface of the body without any structural adaptations. However, in the majority of athoracic (flatworms) and protocavitary invertebrates, the body parenchyma has a system of primary excretory tubes - protonephridia. This is a system of very thin tubules running inside long cells. One end of the tubule sometimes opens on the surface of the body, the other is closed by special process cells. From the surrounding tissues, cells absorb liquid metabolic products and move them along the tubules with the help of flagella lowered into the tubule. The actual excretory function here is inherent in the cells. The tubules are only excretory pathways.

With the appearance of the coelom, the secondary body cavity (in the larvae of annelids), the protonephridial system becomes morphologically associated with it. The walls of the tubules protrude somewhat as a whole and are washed by tissue fluid. The function of selective absorption and excretion of metabolic products passes to them. Process cells are reduced. They retain ciliated flagella that move fluid along the tubule. Subsequently, the closed end of the tubule breaks through an opening into the secondary body cavity. A flickering funnel is formed. The tubules themselves thicken, lengthen, and bend, continuing from one segment of the coelom to another (the coelom is segmented). These modified tubules are called nephridia. The latter are located metamerically on two sides of the body and are connected to each other by their terminal sections. This leads to the formation of a longitudinal duct on each side of the body - a primitive ureter, into which all segmental nephridia are torn off along its course. The primitive ureter opens outward either through an independent opening or into the cloaca. In the body cavity, next to the nephridia, blood vessels form a dense network of capillaries in the form of glomeruli. The excretory system of primitive chordates - lancelets, cyclostomes, and fish larvae - has a similar structure. It is located in the front part of the animal’s body and is called the preference, or head kidney.

The further course of changes in the excretory system is characterized by a gradual shift of its elements in the caudal direction with the simultaneous complication of structures and formation into a compact organ. A pelvic or definitive kidney and a trunk or intermediate kidney appear. The intermediate kidney functions throughout life in fish and amphibians, and during the embryonic period of development in reptiles, birds and mammals. Definitive kidney or metanephros develops only in reptiles, birds and mammals. It develops from two rudiments: urinary and urinary. The urinary part is formed by nephrons - complex convoluted urinary tubes, bearing at the end a capsule into which the vascular glomerulus protrudes. Nephrons differ from the tubules of the trunk kidney in their greater length, tortuosity, and a large number of capillaries in the vascular glomerulus. Nephrons and the blood vessels that surround them are united by connective tissue into a compact organ. The urinary part develops from the posterior end of the duct of the intermediate kidney and is called definitive ureter. Growing to a compact mass of nephrogenic tissue, the ureter forms the renal pelvis, stalks and calyces and comes into contact with the urinary tubules of the kidney. At the other end, the definitive ureter unites with the genital canal into the urogenital canal and in reptiles, birds and monotreme mammals opens into the cloaca. In placental mammals, it opens with an independent opening of the urogenital canal (sinus). The intermediate section of the outflow tract between the ureter and the genitourinary canal forms a pouch-like expansion - the bladder. It is formed in placental mammals from areas of the walls of the allantois and cloaca at the place of their contact.

During ontogenesis in mammals, nephrogenic tissue differentiates in the region of the segmental legs of the mesoderm of all somites sequentially, starting from the head and ending with the pelvic. At the same time, during the intrauterine development of an individual, first the head kidney is formed, then the trunk and, finally, the pelvic kidney with their characteristic structures. The kidney is formed at an early stage of embryo development in the area of ​​the first 2–10 somites from the material of the segmental legs, exists for several tens of hours and does not function as a urinary organ. During the process of differentiation, the material of the segmental legs is detached from the somites and extended towards the ectoderm in the form of tubes that maintain connection with the coelum. This is the renal tubule with the funnel facing the whole. The opposite ends of the tubules merge and form tubular ducts running caudally. Soon the preference is reduced. At the base of its ducts, oviducts are formed. After the formation of the bud, the nephrogenic tissue of the next 10–29 segments begins to differentiate with the formation of an intermediate (trunk) kidney. The intermediate kidney functions as an excretory organ. Excretory products (urea, uric acid, etc.) flow through the duct of the intermediate kidney into the cloaca, and from there into the allantois, where they accumulate.

By the end of the embryonic period, rapid growth and differentiation of the nephrogenic tissue of the posterior segments - the pelvic kidney - occurs. The function of the mesonephros attenuates. Nephrons begin to form from the 3rd month, and their new formation continues not only during uterine development, but also after birth (in a horse up to 8 years, in a pig up to 1.5 years). Nephron differentiation begins with the formation of the renal corpuscle. Then the nephron tubule and finally the collecting duct develop. During the fetal period, the mass of the kidneys increases 94 times, from birth to adulthood - 10 times. The relative mass of the kidneys decreases from 0.4 to 0.2%. Simultaneously with the formation of the definitive kidney, a diverticulum grows from the duct of the intermediate kidney - the rudiment of the ureter. Growing into the nephrogenic rudiment, it forms the pelvis and renal calyces. The bulk of nephrons develop in the peripheral parts of the kidney - in the cortex. The cortex grows very intensively at the beginning of the fetal period. Then, in terms of growth rate, it is overtaken by the medulla - the central parts of the organ, where the structures that drain urine are concentrated. In newborn animals, compared to adults, the cortical layer is poorly developed. Its growth and nephron differentiation occur actively in the first year of life and continue, although with less intensity, until puberty. In old animals, cellular renewal processes in the kidney are disrupted, and the ability of the renal epithelium to reabsorb substances is reduced.

Types of kidneys

In the process of phylogenesis of animals of different families and genera, several types of definitive bud were formed, depending on the degree of fusion of its sections:

1. multiple

2. sulcal multipapillary

3. smooth multipapillary

4. smooth unipapillary

Multiple kidney most fragmented. It consists of individual kidneys (up to 100 or more), united by layers of connective tissue and a capsule into a single compact organ. Each kidney consists of a cortex and medulla and is connected to its own calyx. A stem extends from each calyx. The stalks unite into the ureter, which drains urine from the kidney. Multiple kidneys are characteristic of bears, otters, and cetaceans.

In a grooved multipapillary bud individual buds - kidney lobules are connected to each other by middle sections. The cortical substance of the lobules is delimited by grooves from each other, and the medulla forms a large number of papillae, each of which is lowered into its own calyx. Such kidneys are found in cattle.

IN smooth multipapillary buds the cortex of the renal lobes has merged, and the medulla forms separate papillae. These are the kidneys of a pig and a human.

IN smooth single-papillary buds not only the cortex, but also the medulla merged to form one large roll-shaped papilla. Most mammals have such kidneys, and among domestic animals, horses, small cattle, and dogs.

Kidney structure

Bud– hep – in most cases bean-shaped, brown-red in color. On the kidney, there are dorsal and ventral surfaces, lateral and medial edges, cranial and caudal ends. On the medial edge there is a depression - hilum of the kidney leading to the renal fossa - sinus. Arteries enter the portal of the kidney, veins and the ureter exit. The sinus contains the pelvis and other branches of the ureter. On top, the kidney is covered with a fibrous capsule, which grows tightly only in the area of ​​the hilum. A large amount of adipose tissue accumulates on top of the capsule and in the sinus of the kidney, forming the fatty capsule of the kidney. The ventral surface of the kidney is covered with a serous membrane. On a longitudinal section in the kidney, 3 zones are visible: cortical, medullary and intermediate. Cortical zone lies on the periphery, is brown-red in color and is urinary, as it mainly consists of nephrons. Brain zone lies in the central parts of the organ, is brownish-yellowish in color and is urinary. Border zone located between the cortical and medullary zones, dark red in color, contains a large number of large vessels.

Fig.1. Kidneys and adrenal glands of cattle from the ventral surface

1 – right adrenal gland; 2 – left adrenal gland; 3 – right kidney; 4 – left kidney; 5 – caudal vena cava; 6 – abdominal aorta; 7 – right ureter; 8 – left ureter; 9 – right renal artery and vein; 10 – left renal artery and vein; 11 – caudal adrenal branch of the right renal artery; 12 – caudal suprarenal branch of the left renal artery.

The kidneys of cattle are oval and belong to the type of grooved multipapillary. The fibrous capsule of the kidney extends deep into the grooves. The cranial end of the kidney is narrower than the caudal one. The kidney hilum is wide. The left kidney is twisted longitudinal axis, hangs on the mesentery, which allows it to move behind the right kidney when the scar fills. The mass of each kidney is 500–700 g, and the relative mass is 0.2–0.3%. The cortical urinary zone of the kidney is divided into lobes. The border zone is well defined. The medullary zone in each lobe has the shape of a pyramid, with its base directed towards the cortical zone, and its apex, called papilla, - into a cup. There are 16–35 renal pyramids in the kidney of cattle. The apices of the renal papillae are dotted with papillary openings through which urine flows into the renal calyces - the final branches of the ureter. From the calyces, urine flows down the stalks into two ducts, which in the area of ​​the hilum are combined into one ureter. The right kidney is in contact with the liver, lies at the level from the 12th rib to the 2nd–3rd lumbar vertebrae, the left kidney – from the 2nd to the 5th lumbar vertebrae. Innervated by the vagus and sympathetic nerves. Vascularized by the renal artery.

Fig.2. Pig kidneys and adrenal glands from the dorsal surface

1 – left kidney; 2 – right kidney; 3 – left adrenal gland; 4 – right adrenal gland; 5 – left ureter; 6 – abdominal aorta; 7 – caudal vena cava; 8 – right ureter; 9 – right middle adrenal artery; 10 – left middle adrenal arteries; 11 – left renal artery and vein; 12 – right renal artery and vein.

The pig's kidneys are smooth, multi-spectacled, bean-shaped, dorsoventrally flattened. There are 10–12 pyramids, the same number of papillae. Some papillae may become fused. The papillae are approached by calyxes that open directly into the renal pelvis, located in the sinus of the kidney. Both kidneys lie in the lumbar region at the level of 1–4 lumbar vertebrae.

The horse's kidneys are smooth and single-papillary. The right kidney is heart-shaped, the left is bean-shaped. The border zone is wide and well defined. The number of renal pyramids reaches 40–64. The papillae are fused into one, directed into the renal pelvis. The right kidney lies almost entirely in the hypochondrium, at the level from the 16th (14–15th) rib to the 1st lumbar vertebra. The left kidney lies at the level of 1–3 lumbar vertebrae and rarely extends into the hypochondrium.

Rice. 3. Horse kidneys from the ventral surface

1 – right kidney; 2 – left kidney; 3 – right adrenal gland; 4 – left adrenal gland; 5 – caudal vena cava; 6 – abdominal aorta; 7 – celiac artery; 8 – right renal artery and vein; 9 – cranial mesenteric artery; 10 – left renal artery and vein; 11, 12 – renal lymph nodes; 13 – right ureter; 14 – left ureter.

Histological structure. The kidney is a compact organ. The stroma forms a capsule and thin layers inside the organ, which run mainly along the vessels. Parenchyma is formed by epithelium, the structures of which can function only in close contact with the circulatory system. All types of kidneys are divided into lobes. A lobe is a renal pyramid with a portion of the cortex covering it. The lobes are separated from each other by renal columns - areas of the cortex penetrating between the pyramids. The lobes consist of lobes that do not have clear boundaries. A lobule is a group of nephrons flowing into one collecting duct, which runs through the center of the lobule and is called the medullary ray because it descends into the medulla. In addition to the branching collecting duct, the medullary ray contains straight tubules (loops) of the nephron.

Nephron – the main structural and functional unit of the kidney. There are up to 8 million nephrons in the kidneys of cattle. 80% of them are located in the cortex - these are cortical nephrons. 20% are located in the medulla and are called juxtamedullary. The length of one nephron is from 2 to 5 cm. The nephron is formed by single-layer epithelium and consists of nephron capsule, proximal part, nephron loop (Henle) and distal part. The nephron capsule has the appearance of a double-walled bowl, its inner wall (inner leaf) is closely connected with the blood capillaries. The outer layer of the capsule is composed of single-layer squamous epithelium. Between the leaves of the capsule there is a slit-like capsule cavity. The capillaries anastomose with each other, forming a vascular glomerulus of 50≈100 loops. Blood enters the glomerulus through the afferent arteriole. The capillaries of the glomerulus unite to form the efferent arteriole. The arrangement of capillaries between two arterioles is called wonderful arterial system kidneys

The nephron capsule together with the glomerulus is called renal corpuscle. All renal corpuscles are located in the renal cortex. In the renal corpuscle, the formation of primary urine, the glomerular filtrate, occurs by filtering the components of the blood plasma. This becomes possible due to the structural features of the renal corpuscle. The afferent arteriole has a lumen of a larger diameter than the efferent arteriole. This creates increased pressure in the capillaries of the glomerulus. In the endothelium of the capillaries there are cracks and numerous fenestrae - similar to very small pores, which facilitates the leakage of plasma. The epithelium of the inner layer of the capsule is closely adjacent to the endothelium of the capillaries, repeating all their bends, separated only by the basement membrane. It is formed by peculiar flat process cells with a diameter of 20–30 microns - podocytes. Each podocyte has several large processes - cytotrabeculae, from which numerous small processes - cytopodia - attach to the basement membrane. There are gaps between the cytopodia. As a result, a biological kidney filter is formed with selective ability. Normally, blood cells and large protein molecules do not pass through it. The remaining parts of the plasma can become part of the primary urine, which therefore differs little from blood plasma. The amount of primary urine - glomerular filtrate in large animals is several hundred liters per day. The glomerular filtrate enters the lumen of the renal corpuscle capsule, and from there into the nephron tubule. It undergoes reverse selective absorption into the bloodstream - reabsorption components of the glomerular filtrate, so that the secondary urine removed from the body is only 1–2% in volume of the primary urine and does not at all correspond to it in chemical composition. Secondary urine contains 90 times less water and sodium, 50 times less chlorides, 70 times more concentration of urea, 30 times more phosphates, 25 times more uric acid. Sugar and protein are normally absent. Reabsorption begins and most actively occurs in the proximal nephron.

Part proximal part The nephron includes a proximal convoluted tubule and a straight tubule, which at the same time is part of the nephron loop. The lumen of the renal corpuscle capsule passes into the lumen of the proximal convoluted tubule. Its walls are formed by single-layer cubic epithelium, which is a continuation of the epithelium of the outer layer of the nephron capsule. The proximal convoluted tubules have a diameter of about 60 μm, lie in the cortex, curving in close proximity to the renal corpuscle. The cells of the proximal convoluted tubule at the apical pole, facing the lumen of the tubule, bear a large number of microvilli that form a brush border - a device for the active absorption of substances. The rounded nucleus is shifted to the basal pole. The plasmalemma of the basal pole forms deep invaginations in the form of folds into the cell. Between these folds lie elongated mitochondria in rows. At the light level, these structures have the appearance of basal striations. The cells actively absorb glucose, amino acids, water and salts and have a cloudy, oxyphilic cytoplasm. Throughout the proximal section, the entire amount of sugar, amino acids and small protein molecules trapped in the glomerular filtrate, 85% of water and sodium are reabsorbed.

The proximal convoluted tubule becomes nephron loop (Henle). This is a straight tubule that extends into the medulla to varying depths. The nephron loop has descending and ascending parts. The descending part is first formed by cuboidal epithelium, the same in structure and function as in the proximal convoluted tubule, and therefore this section is also included in the proximal nephron as its straight tubule. The lower portion of the descending part of the nephron loop has a diameter of 15 μm, is formed by squamous epithelium, the nuclei of which protrude into the lumen of the tubule and is called the thin tubule. Its cells have light cytoplasm, few organelles, single microvilli and basal striations. The thin tubule of the nephron loop continues into its ascending part. It absorbs salts and removes them into tissue fluid. In the upper section, the epithelium becomes cubic and passes into the distal convoluted tubule with a diameter of up to 50 μm. The thickness of its walls is smaller, and the lumen is larger than in the proximal convoluted tubule.

Walls distal convoluted tubule formed by cuboidal epithelium with light cytoplasm without a brush border, but with basal striations. Reabsorption of water and salts occurs in it. The distal convoluted tubule is located in the cortex and one of its sections is in contact with the renal corpuscle between the afferent and efferent arterioles. In this place called dense spot, the cells of the distal convoluted tubule are tall and narrow. They are thought to sense changes in sodium levels in the urine. During normal kidney function, 30–50% of nephrons are actively functioning. When diuretics are administered – 95–100%.

Juxtamedullary nephrons differ in structure and function from cortical nephrons. Their renal corpuscles are larger and lie in deep areas of the cortex. The afferent and efferent arterioles have the same diameter. The nephron loop, especially its thin tubule, is much longer, reaching the deep layers of the medulla. In the area of ​​the macula densa there is a juxtaglomerular (periglomerular) apparatus - an accumulation of several types of cells, together forming endocrine kidney complex, regulating renal blood flow and urine formation. It is involved in the synthesis of renin, a hormone that stimulates the production of vasoconstrictor substances (angiotensins) in the body, and also stimulates the production of the hormone aldosterone in the adrenal glands. From the distal nephron, urine enters the collecting duct.

Collecting ducts are not components of nephrons. These are the terminal branches of the ureter, penetrating the kidney parenchyma and fused with the ends of the nephrons. The areas of the collecting ducts lying in the cortex are formed by cuboidal epithelium with very light cytoplasm, in the medulla - by columnar epithelium. Some absorption of water continues in the collecting ducts due to the hypertonicity of the surrounding tissue fluid. As a result, the urine becomes even more concentrated. The collecting ducts form a branched system. They pass in the center of the medullary rays of the cortex and in the medulla and unite into papillary ducts, opening with holes at the top of the papillae.

Rice. 5. Diagram of the kidney structure

1 – kidney capsule; 2 – arcuate artery; 3 – renal artery; 4 – renal vein; 5 – renal pelvis; 6 – renal calyx; 7 – ureter; 8 – urine; 9 – cortex; 10 – brain zone.

Blood supply to the kidney carried out by a large paired renal artery, which enters the kidney in the hilum area and branches into interlobar arteries. In the border zone of the kidney they become the arcuate arteries. From them a large number of interlobular arteries extend into the cortex. These arteries branch into intralobular arteries, from which afferent arterioles branch, branching into the capillaries of the choroid glomerulus. The capillaries gather into the efferent arteriole. Here we see the wonderful arterial system of the kidney– capillaries between two arteries. In these capillaries, blood is filtered with the formation of primary urine. The efferent arteriole again branches into capillaries that intertwine the nephron tubules. Reabsorbed substances enter these capillaries from the nephron tubules. The capillaries unite into veins that carry blood out of the kidney.

Ureters, bladder, urethra

Ureters– ureteres – long narrow tubes running from the hilum of the kidneys to the bladder along the lateral walls of the abdominal cavity. They enter the dorsal wall of the bladder, run obliquely for some time in the thickness of its wall between the muscular and mucous membranes and open into its cavity in the neck area. Because of this, when the bladder is stretched by incoming urine, the ureters are pinched and the flow of urine into the bladder stops. The ureters have a well-developed muscular layer. Thanks to its peristaltic contractions (1-4 times per minute), urine is driven through the ureter to the bladder.

Bladder– vesica urinaria – a hollow pear-shaped organ. It is distinguished by a cranially directed apex, the main part - the body and a narrowed, caudally directed neck. It lies unfilled for days in the pelvic cavity. When full, the top of the bladder descends into the pubic region. The neck of the bladder passes into the urethra.

Urethra– uretra – a short tube that extends from the bladder and flows into the genital tract. In females, it opens with a slit-like opening in the ventral wall of the vagina, after which the common area of ​​the urinary and genital tract is called genitourinary vestibule, or sine. In males, near the beginning of the urethra, the vas deferens flow into it, after which it is called genitourinary canal and opens on the head of the penis.

Rice. 6. Boar bladder

1 – apex of the bladder; 2 – body of the bladder (the serous membrane has been removed); 3 – serous membrane; 4 – outer layer of the muscle membrane; 5 - middle layer muscle membrane; 6 – inner layer of the muscle membrane; 7 – mucous membrane of the bladder; 8 – ureteral cushion; 9 – opening of the ureter; 10 – bladder triangle; 11 – ureteral folds; 12 – adventitia; 13 – sphincter of the bladder; 14 – urethral ridge; 15 – mucous membrane of the urethra; 16 – seminal mound; 17 – urethra (urethra); 18 – layer of smooth muscle tissue; 19 – urethral muscle.

Histological structure of the urinary tract

The ureters, bladder and urethra are tube-shaped organs. Their mucous membrane is lined with stratified transitional epithelium. The lamina propria of the mucous membrane is formed by loose connective tissue. The muscular layer is formed by smooth muscle tissue and is well developed, especially in the ureters and bladder, where it forms three layers: the outer and inner - longitudinal, the middle - annular. Due to the annular layer in the area of ​​the bladder neck, a sphincter is formed. Externally, the ureters and the cranial part of the bladder (apex and body) are covered with a serous membrane. The caudal part of the bladder (neck) and the urethra are covered with adventitia.