The urination system serves to cleanse the blood of harmful products (mainly protein, salt metabolism, water) in the form of urine, remove it from the body and maintain a constant blood composition. The urinary organs include the kidneys, ureters, bladder, and urethra. The kidneys are the urinary organs, and the rest make up the urinary tract. Together with urine, more than 80% of the end products of metabolism are excreted from the body. The kidneys also perform an endocrine function. A number of hormones are synthesized in them: erythropoietin (stimulates erythropoiesis), prostaglandins and bradykinin (the main function of these hormones is the regulation of blood flow in the kidney), renin, etc.
STRUCTURE AND TYPES OF THE KIDNEYS
gene (perigoya) - paired organ, bean-shaped, dense texture, red-brown color. The kidneys are located in the abdominal cavity on the sides of the spinal column, in the lumbar region between the lumbar muscles and the parietal sheet of the peritoneum. They lie in the region of the center of gravity of the third quarter of the body of the animal, and therefore, are located in the center of relative rest (Fig. 6.1).The kidney is covered with a dense fibrous capsule, which loosely connects to the parenchyma of the kidney, is surrounded on the outside by a fatty capsule, and on the underside is covered, in addition, by a serous membrane - the peritoneum. On the inner surface there is a recess - the gates of the kidneys, through which vessels and nerves enter the kidneys, veins and ureters exit. In the depths of the gate is the renal cavity, the renal pelvis is placed in it.
Three zones are distinguished in the kidneys: cortical (urinary), borderline (vascular) and cerebral (urinary).
The cortical zone is dark red, located on the periphery. It contains convoluted urinary tubules - nephrons - structural and functional units of the kidneys, where all the processes of blood purification and urine formation take place. The renal corpuscle consists of a vascular glomerulus and a two-layer capsule, which passes into the convoluted tubule. The renal artery branches into the interlobar arteries, from which the arcuate arteries depart. These arteries form
Rice. 6.1.
a- cattle; b- pigs; v- horses (with ureters and bladder);
- 1 - kidneys; 2 - adrenal gland; 3 - abdominal aorta; 4 - ureter;
- 5 - the top of the bladder; 6 - the body of the bladder;
- 7 - mucous membrane of the bladder (organ opened); 8 - renal lobule; 9 - renal pyramid; 10 - urinary area;
- 11 - border zone; 12 - urine diverting zone;
- 13 - renal papilla: 14, 15 - stalks
[Pismenskaya V.N., Boev V.I. Workshop on anatomy and histology of farm animals. M.: KolosS, 2010. S. 201]
the border zone, which in the form of a dark-colored strip separates the cortical zone. Radial arteries depart from the arcuate arteries to the cortical zone. Along them lie the renal corpuscles, the rows of which are separated from each other by the brain rays. The terminal branches of the radial arteries form a network of arterial capillaries that form vascular glomeruli. The cerebral zone lies in the center of the kidney, it is lighter, divided into renal pyramids. The bases of the pyramids face the periphery. Brain rays come out of them into the cortical zone. The opposite ends of the pyramids - the tops - form one or more renal papillae. The tubules that conduct urine open into the renal calyces (in ruminants, pigs) or the renal pelvis (in horses, sheep).
The following types of kidneys are distinguished: multiple, striated multi-papillary, smooth multi-papillary, smooth single-papillary (Fig. 6.2).
Rice. 6.2. Scheme of the structure of nights of different types: a- multiple kidney; 6 - furrowed multipapillary kidney; v- smooth multipapillary kidney; G- smooth single-papillary kidney;
I - kidney; 2 - stalks of the ureter; 3 - ureter;
- 4 - renal papilla; 5 - renal calyx; 6 - renal grooves;
- 7 - pelvis; 8 - common papilla; 9 - cut arcuate vessels;
I- urinary layer; II- boundary layer;
III- urine-diverting layer
[Pismenskaya V.N., Boev V.I. Workshop on anatomy and histology of farm animals. M.: KolosS, 2010. S. 202]
Multiple kidney consists of many individual small kidneys. Each bud has a hollow stem. The stalks join into large branches that flow into the common ureter. In the area of its exit is the renal fossa. Such a structure has the kidneys of the fruits of cattle.
V furrowed multipapillary kidneys individual kidneys grow together with their middle sections. Outside, the kidney is divided by grooves into separate lobules, and numerous papillae are visible on the cut. The renal pelvis is absent, and therefore the stalks in the kidneys open in two main passages, and the latter form a common ureter. Such a structure have kidneys in cattle.
V smooth multipapillary kidneys the surfaces are smooth, since the cortical zone has merged completely, and the renal pyramids with the papilla are visible on the cut. The renal calyces open into the renal pelvis, from which the ureter emerges. Pigs have such kidneys.
Smooth single papillary buds are characterized by the fusion of the cortical and cerebral zones with one common papilla protruding into the renal pelvis. Such kidneys are found in horses, small ruminants, deer, and rabbits. Kidneys are classified as offal category I.
The incidence of kidney infections is not properly detected and farmers do not receive sufficient information about the reasons for the decline in livestock
Early recognition and treatment of kidney disease often leads to a favorable outcome. The strength of these organs in cattle is quite great, so that you can not notice any signs of disease for a long time until they are affected by two-thirds.
Kidney intoxication can occur for a variety of reasons, but this article focuses specifically on infectious diseases of the organ, namely what veterinarians generally call pyelonephritis (infection and pus in the kidneys).
Infection occurs when bacteria enter the bloodstream, from where they go directly to the kidneys. After all, the main function of the kidneys is to filter the blood. Another way is through the ureters, the partial blockage of which encourages the growth and multiplication of bacteria.
Livestock acquires kidney infections individually. Sources may be different (through the mother's placenta, feeding, after suffering from pneumonia, etc.) These infections reduce immunity and allow bacteria to gain access to the kidneys.
The first sign of kidney disease in cattle is weight loss. I (Roy Lewis) have seen many similar cases in late pregnancy and just after calving. The kidneys of a pregnant cow have a double load, they must filter not only their own blood, but also the blood of future calves. These increased loads greatly affect the ability of the kidneys to filter, so this is the ideal time for infection to enter. In cows that bear two calves at the same time, the load on the organs doubles.
Taking a cow to the vet after weight loss is not a complete solution. The veterinarian can palpate the left kidney and ureters (the tubes that run from the kidneys to the bladder). You can also take a urine sample and check for blood, bacteria, pus deposits, and other parameters that will either confirm or rule out a kidney infection. Blood tests may show elevated levels of white blood cells. Other indicators, such as nitrogenous urea (BUN) will only grow even after each of the kidneys is deformed separately, and then the result will be very deplorable.
My experience is that if cattle are still eating and drinking well, then early diagnosis and timely treatment promise a favorable prognosis. If there is no appetite and the BUN score is high, despite intensive treatment, including intravenous injections, then the worst is to be expected.
Cases have become more frequent
There are many kidney diseases, many more than we can imagine. It became obvious to me after I saw a huge number of dissected cows as part of the BSE research program. Both kidneys were infected, and the left one barely functioned.
The classic scenario is that the farmer notices that the cow has lost weight, but does not notice other symptoms, after which the cow stops eating and soon dies.
Most of the sick cows can be saved and returned to normal life, or at least sent to slaughter ahead of time. I am convinced that the number of cows that die on farms from undiagnosed kidney disease cannot be accurately determined.
Growers may notice increased frequency of urination or pain when urinating.
Look closely at the urine, especially towards the end of urination (for blood and pus, or just redness).
This may be the key that will move us forward in the search for infection.
The appearance of reddish urine in cattle can be due to many reasons. For example, due to bacterial hemoglobinuria or phosphorus deficiency, or simply colored with red clover. All these and many other causes of red urine can sometimes complicate the diagnosis.
Treatment
The most common bacterium that causes kidney disease in cattle is well killed by penicillin. There are two main keys to successful treatment. First, it is necessary (the sooner the better) to detect the disease; before the kidneys are severely damaged. Secondly, the duration of treatment should correspond to the time of complete recovery in order to avoid re-infection.
This will definitely require treatment with injections of penicillin and novocaine in the early days, until the first noticeable improvement. Then several long-acting drugs in the next two weeks.
A common mistake is also to stop the treatment too early when the situation improves and the urine clears.
This is a smoldering infection and may return if not completely cured. Like any relapse, it is much more difficult to treat, as the infection has settled deeper.
Such cattle are like a time bomb: weakened kidneys make them unsuitable for breeding, and they can also fail kidneys. It is better even to score them before their condition worsens.
Kidney infections can occasionally be found in pastures in the prairie zone.
Each herd periodically faces these problems, however, careful monitoring of the condition of the animals, timely intervention and the right treatment will be rewarded.
Penicillin is by far the most effective drug, it passes through the kidneys and is excreted through the urine.
If your herd is losing weight, contact your veterinarian to check the cows and prescribe the appropriate treatment.
Let's admit that timely diagnosis and treatment is not so expensive, effective and, at current livestock prices, economically justified.
| Animal | Palpation | Topography | Structure | Mobility |
| Horse | Internal | Right kidney: from the 14th-15th rib to the last lumbar vertebrae Left kidney: from the last rib to the 3rd-4th lumbar vertebrae | Smooth, right kidney heart-shaped | |
| cattle | Internal | Right kidney: from the 12th rib to the 2nd - 3rd lumbar vertebrae. Left kidney: 3rd – 5th lumbar vertebra | bumpy | The left kidney is mobile |
| MRS | outdoor | .Right kidney: up to 1 - 3 lumbar spine. Left kidney: 4–6 lumbar vertebra | bumpy | motionless |
| Pig | Difficulty | 1-4 lumbar vertebrae | Smooth | motionless |
| Dog | outdoor | 1-4 lumbar vertebrae | Smooth | motionless |
| Cat | outdoor | 1-4 lumbar vertebrae | Smooth | motionless |
The topography of the kidneys is associated with the species characteristics of animals, with the nature of the structure and location of the abdominal organs. The location of the kidneys can be affected by the state of the abdominal organs, as normal (for example, displacement of the left mobile kidney of ruminants when the scar is filled) or if there are pathological processes in them. Displacement of the kidneys is observed with the development of inflammatory processes in nearby organs, with their hypertrophy, them neoplasms..
An increase in the kidneys is possible with the development of inflammatory processes in them (paranephritis, nephritis, pyelonephritis), in the presence of congenital anomalies of the structure (polycystic, hydronephrosis), with the development of neoplasms, as well as with compensatory hypertrophy of one of the kidneys, with insufficient function or removal of the second.
A decrease in kidney size is much less common. This phenomenon occurs with congenital underdevelopment of the kidneys (congenital hypoplasia of the kidneys), as well as due to chronic inflammatory processes, atrophic and degenerative changes in the renal parenchyma.
A change in the relief or structure of the kidneys is observed in the presence of tumors, cysts, abscesses in them. In chronic inflammatory processes (chronic glomerulonephritis, chronic pyelonephritis) and degenerative changes (nephrosclerosis, amyloidosis), the kidneys become dense.
Soreness of the kidneys is observed in acute inflammatory processes, kidney injuries, urolithiasis.
Percussion of the kidneys . The diagnostic value of percussion of the kidneys is primarily for identifying pain when tapping in the lumbar region. In large animals, percussion is carried out with a hammer with a plessimeter, and in small animals - digitally. In cattle, only the right kidney can be percussed. When applying sharp, mild blows to the surface of the lower back in the area of the projection of the kidneys, one can establish their soreness by the behavior of the animal. If a sick animal feels pain when tapping, then they talk about positive symptom of Pasternatsky, and if not, negative. A positive symptom of Pasternatsky is determined in nephrolithiasis, paranephritis, pyelonephritis and other inflammatory diseases of the kidneys, as well as in myositis and radiculitis, which significantly reduces its diagnostic value.
Functional methods for examining the kidneys . These methods are not widely used in veterinary practice and are used mainly for experimental purposes.
1) Determination of the relative density of urine(Zimnitsky test). This test involves the collection of eight portions of urine (every 3 hours) with voluntary urination and a certain water regime in order to determine the volume and relative density of urine of each portion. Further, comparing the amount of urine in the night and daytime portions, they learn about the predominance of nighttime and daytime diuresis. In a healthy animal, daytime diuresis significantly exceeds nighttime diuresis and amounts to 2/3 - 2/4 of the total amount of daily urine. With functional failure of the kidneys, nocturnal diuresis predominates, which indicates an increase in the time of the kidneys due to a decrease in their functional ability. Investigating the density and volume of various portions, they judge their fluctuations during the day and the maximum value. If in the Zimnitsky sample the maximum value of relative density is 1.012 or less, or there is a limitation of relative density fluctuations within 1.008 - 1.010, then this indicates a pronounced violation of the concentration ability of the kidneys. This state is called isosthenuria, which means the loss of the ability of the kidneys to excrete urine of a different osmolarity, except as equal to the osmolarity of the protein-free plasma filtrate. The phenomenon of isosthenuria is characterized by the release of watery, colorless and odorless urine.
The human body is a reasonable and fairly balanced mechanism.
Among all infectious diseases known to science, infectious mononucleosis has a special place ...
The disease, which official medicine calls "angina pectoris", has been known to the world for quite a long time.
Mumps (scientific name - mumps) is called an infectious disease ...
Hepatic colic is a typical manifestation of cholelithiasis.
Cerebral edema is the result of excessive stress on the body.
There are no people in the world who have never had ARVI (acute respiratory viral diseases) ...
A healthy human body is able to absorb so many salts obtained from water and food ...
Bursitis of the knee joint is a widespread disease among athletes...
The structure of the kidneys of mammals
KIDNEYS | Encyclopedia Around the World
Also on topic
- 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 vertebrate kidneys in structure and evolutionary origin.
Function.
The main function of the kidneys is to remove water and end products of metabolism from the body. In mammals, the most important of these products is urea, the main nitrogen-containing end 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 feces. In humans, uric acid is also formed and excreted by the kidneys (its salts are called urates).
Human kidneys excrete about 1-1.5 liters of urine per day, although this value can vary greatly. The kidneys respond to an increase in water intake by increasing the production of more dilute urine, thereby maintaining a normal water content in the body. If water intake is limited, the kidneys help retain water in the body by using as little water as possible to form 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, with an excess of water in the body, ADH is not excreted and the daily volume of urine can reach 20 liters. Urine excretion, however, does not exceed 1 liter per hour.
Structure.
Mammals have two kidneys located in the abdomen on either side of the spine. The combined weight of two kidneys in humans is about 300 g, or 0.5–1% of body weight. Despite their small size, the kidneys have an abundant blood supply. Within 1 min, 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 cortical and medulla. Most of the substance of the kidney consists of a huge number of the thinnest 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 twisted part closest to the glomerulus is the proximal convoluted tubule. Next is a thin-walled straight section, which, turning abruptly, forms a loop, the so-called. loop of Henle; it distinguishes (sequentially): a descending section, a bend, an ascending section. The twisted 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 (in fact, the expanded end of the ureter) and further along the ureter into the bladder. Urine is expelled from the bladder through the urethra at regular intervals. The cortex contains all the glomeruli and all the convoluted portions of the proximal and distal tubules. In the medulla lie the loops of Henle and the collecting ducts located between them.
Urine formation.
In the renal glomerulus, water and substances dissolved in it, under the action of arterial pressure, leave the blood through the walls of the capillaries. The pores of the capillaries are so small that they trap blood cells and proteins. Consequently, the glomerulus works 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 the total human blood volume is approximately 5 liters, it is obvious that most of the ultrafiltrate must be reabsorbed 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.
The ultrafiltrate contains many valuable substances (salts, glucose, amino acids, vitamins, etc.) that the body cannot lose in significant quantities. Most of them are reabsorbed (reabsorbed) as the filtrate passes through the proximal tubules of the nephron. Glucose, for example, is reabsorbed until it completely disappears from the filtrate, i.e. until its concentration approaches zero. Since the transfer 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 OSMOS). This is called passive transport. With the help of active and passive transport, 7/8 of the water and substances dissolved in it are reabsorbed 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 intratubular fluid contains mainly "slags", such as urea, but the process of urine formation is not yet over.
The next segment, the loop of Henle, is responsible for creating very high concentrations of salts and urea in the filtrate. In the ascending section of the loop, there is an active transport of dissolved substances, primarily salts, into the surrounding tissue fluid of the medulla, where as a result a high concentration of salts is created; due to this, part of the water is sucked out from the descending bend of the loop (permeable to water) and immediately enters the capillaries, while salts gradually diffuse into it, reaching the highest concentration in the bend of the loop. This mechanism is called countercurrent concentrating mechanism. Then the filtrate 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 will be the final volume of urine, i.e. the volume of the 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 action of ADH, their walls become permeable to water. Since the concentration of salts in the loop of Henle is very 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 impermeable 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 that have difficulty accessing drinking water. A kangaroo rat, for example, living in the desert in the southwestern United States, excretes urine 4 times more concentrated than that of a person. This means that the kangaroo rat is able to excrete toxins in a very high concentration, using a minimal amount of water.
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KIDNEYS
Kidney - gene (nephros) - a paired organ of a dense consistency of red-brown color. The kidneys are built according to the type of branched glands, located in the lumbar region.
The kidneys are rather large organs, approximately the same on the right and left, but not the same in animals of different species (Table 10). In young animals, the kidneys are relatively large.
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 margin, vessels and nerves enter the kidney and the ureter exits. This place is called the hilum of the kidney.
10. Weight of kidneys in animals
Rice. 269. Urinary organs of cattle (from the ventral surface)
Outside, the kidney is covered with a fibrous capsule, which is connected to the parenchyma of the kidney. The fibrous capsule is surrounded on the outside by a fatty capsule, and from the ventral surface, in addition, it is covered with a serous membrane. The kidney is located between the lumbar muscles and the parietal sheet 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 region 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 2nd-5th lumbar vertebrae; when the scar is filled, it shifts slightly to the right.
From the surface, the kidneys of cattle are divided by furrows into lobules, of which there are up to 20 or more (Fig. 270, a, b). The striated structure of the kidneys is the result of incomplete fusion of their lobules in embryogenesis. On the section of each lobule, the cortical, cerebral and intermediate zones are distinguished.
The cortical, or urinary, zone (Fig. 271, 7) is dark red in color, located superficially. It consists of microscopic renal corpuscles arranged radially and separated by streaks of brain rays.
The cerebral, or urinary, zone of the lobule is lighter, radially striated, located in the center of the kidney, shaped like a pyramid. The base of the pyramid faces outward; from here brain rays go to the cortical zone. The top of the pyramid forms the renal papilla. The brain zone of adjacent lobules is not divided by furrows.
Between the cortical and cerebral zones in the form of a dark strip is an intermediate zone. Arc arteries are visible in it, from which radial interlobular arteries are separated into the cortical zone. Along the latter 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 a special excretory tissue. The efferent artery emerges from the vascular glomerulus. It forms a capillary network on the convoluted tubule, which starts from the glomerular capsule. Renal corpuscles with convoluted tubules make up the cortical zone. In the region of the brain rays, the convoluted tubule passes into the straight tubule. The collection of direct tubules forms the basis of the medulla. Merging with each other, they form the papillary ducts, which open at the top of the papilla and form a lattice field. The renal corpuscle together with the convoluted tubule and its vessels make up the structural and functional unit of the kidney - the nephron - nephron. In the renal corpuscle of the nephron from the blood of the vascular glomerulus, a liquid is filtered into the cavity of its capsule - the primary urine. During the passage of primary urine through the convoluted tubule of the nephron, most (up to 99%) of 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. So, in a person in one kidney, there are up to 2 million nephrons.
Kidneys with superficial furrows and many papillae are classified as striated multipapillary. Each papilla is surrounded by a renal calyx (see Fig. 270). Secondary urine secreted into the calyces enters two urinary ducts through short stalks, which join into 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 type of smooth multi-papillary (see Fig. 270, c, d). They are characterized by complete fusion of the cortical zone, smooth from the surface. However, the section shows 10-16 renal pyramids. They are separated by strands of the cortical substance - the renal columns. Each of 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. From the pelvis begins the ureter. The right and left kidneys lie under 1-3 lumbar vertebrae (Fig. 272), the right kidney does not come into contact with the liver. Smooth multi-papillary kidneys are also characteristic of humans.
In a horse, the right kidney is heart-shaped, and the left kidney is bean-shaped, smooth from the surface. The section shows the complete fusion of the cortex and medulla, including the papillae. The cranial and caudal parts of the renal pelvis are narrowed and are called renal passages. Renal pyramids 10-12. Such kidneys belong to the type of smooth single-papillary. 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.
In a dog, the kidneys are also smooth, single-papillary (see Fig. 270, e, e), of a typical bean-shaped form, located under the first three lumbar vertebrae. In addition to the horse and dog, smooth single-papillary kidneys 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 grape-shaped kidneys. Their embryonic lobules remain completely separated throughout the life of the animal and are called kidneys. Each kidney is built according to the general plan of an ordinary kidney; on the cut it has three zones, a papilla and a calyx. The kidneys are connected to each other by excretory tubules that open into the ureter.
After the birth of the animal, the growth and development of the kidneys continue, 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 in them by 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 renal corpuscles increases during the year by 5, and by six years - by 15 times, the convoluted tubules lengthen, etc. At the same time, the relative mass of the kidneys is halved: from 0.51% in newborn calves to 0, 25% in one-year-olds (according to V.K. Birich and G.M. Udovin, 1972). The number of renal lobules remains almost constant after birth.
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Internal structure of mammals Mammalian organ systems
Compared with other amniotes, the digestive system of mammals is characterized by significant complication. This is manifested in an increase in the total length of the intestine, its clear differentiation into sections, and an increase in the 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 a mixed type of nutrition predominate. Eating exclusively animal food is less common and is mainly characteristic of predators. Plant food is used by terrestrial, aquatic and underground mammals. The type of nutrition of mammals determines not only the specifics of the structure of animals, but also in many respects the way of existence, the system of their behavior.
Terrestrial inhabitants use various types of plants and their parts - stems, leaves, branches, underground organs (roots, rhizomes). Among the typical "vegetarians" are ungulates, proboscis, lagomorphs, rodents and many other animals.
Among herbivorous animals, specialization in the consumption of feed is often observed. Many ungulates (giraffes, deer, antelopes), proboscis (elephants) and a number of others feed mainly on leaves or twigs of trees. The juicy fruits of tropical plants form the basis of nutrition for many tree dwellers.
The wood is used by beavers. The food base for mice, squirrels, chipmunks is made up of a variety of seeds and fruits of plants, from which stocks are also made for the wintering period. There are many species that feed mainly on grasses (ungulates, marmots, ground squirrels). The roots and rhizomes of plants consume underground species - jerboas, zokors, mole rats and mole voles. The diet of manatees and dugongs is made up of aquatic grasses. There are animals that feed on nectar (certain types of bats, marsupials).
Carnivores have a wide range of species that make up their prey base. A significant place in the diet of many animals is occupied by invertebrates (worms, insects, their larvae, mollusks, etc.). Insectivorous mammals include hedgehogs, moles, shrews, bats, anteaters, pangolins and many others. Often insects are eaten by herbivorous species (mice, ground squirrels, squirrels) and even rather large predators (bears).
Among aquatic and semi-aquatic animals there are fish-eating (dolphins, seals) and zooplankton-eating (baleen whales). A special group of carnivorous species are carnivores (wolves, bears, felines, etc.), which hunt large animals either alone or in packs. 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 mammalian digestive system 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 for temporary food reservation (hamsters, ground squirrels, chipmunks). In the oral cavity there is a fleshy tongue and heterodont teeth sitting in the alveoli. The tongue performs the function of an organ of taste, participates in the capture of food (anteaters, ungulates) and in its chewing.
Most animals are characterized by a complex dental system, in which incisors, canines, premolars and molars are distinguished. The number and ratio of teeth varies in species with different types of food. So, the total number of teeth in mice is 16, a hare - 28, cats - 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 of the upper jaw, and the denominator - the number of teeth in the lower jaw. For ease of recording, letter designations of different teeth are adopted: incisors - i (incisive), canines - c (canini), premolars - rm (praemolares), molars - m (molares). Predatory animals have well-developed fangs and molars with cutting edges, while herbivorous animals (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 (pinniped 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 canines, part of the premolars, and sometimes incisors.
The formation of a diastema in predatory animals is associated with an increase in 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 secret of which is involved in the wetting of food, contains enzymes for the breakdown of starch and has an antibacterial effect.
Through the pharynx and esophagus, food passes into a well-demarcated stomach, which has a 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 shape and two sections - cardiac and pyloric. In the cardial (initial) section of the stomach, the environment is more acidic than in the pyloric section.
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 departments make up the "prestomach", the walls of which are lined with stratified epithelium without digestive glands. It is intended only for fermentation processes, which are subjected to absorbed herbal mass under the influence of symbiont microbes. This process takes place in an alkaline environment of three departments. Partially processed by fermentation, the mass is burped in portions into the mouth. Careful chewing (chewing gum) enhances the fermentation process when food enters the stomach again. Gastric digestion is completed in the abomasum, 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 considerably depending on the nature of the animal's diet. So, 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. On the border of the small and large intestines there is a caecum, intended for the fermentation process, therefore it is especially well developed in herbivorous animals.
The ducts of the liver and pancreas flow into the first loop of the small intestine - the duodenum. Digestive glands not only secrete enzymes, but also actively participate in metabolism, excretion function 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 the absorption of nutrients into the bloodstream takes place. In the thick section, due to fermentation processes, the processing of hard-to-digest food takes place. 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 is carried out through the skin (about 1% of the total gas exchange) and the respiratory mucosa. The lungs are of the alveolar type. The respiratory mechanism is thoracic, due to the contraction of the intercostal muscles and the movement of the diaphragm - a special muscle layer that separates the chest 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. The 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 released by the mucous membrane of its walls. In this department, a capillary network is well developed, providing a partial supply of oxygen to the blood. The olfactory section contains outgrowths of the walls, due to which a labyrinth of cavities is formed, increasing the surface for trapping odors.
Air passes through the choanae and pharynx into the larynx, which is supported by a cartilage system. In front are unpaired cartilages - the thyroid (characteristic only for mammals) with the epiglottis and the cricoid. The epiglottis covers the entrance to the respiratory tract when food is swallowed. At the back of the larynx lie the arytenoid cartilages. Between them and the thyroid cartilage are the vocal cords and vocal muscles that determine the production of sounds. Cartilage 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 provide gas exchange. The total area of alveolar vesicles significantly (50–100 times) exceeds the body surface, especially in animals with a high degree of mobility and gas exchange. An increase in the respiratory surface is also observed in mountain species that are constantly experiencing oxygen deficiency.
The respiratory rate is largely determined by the size of the animal, the intensity of metabolic processes and motor activity. The smaller the mammal, the relatively higher the loss of heat from the surface of the body and the more intense the level of metabolism and oxygen demand. The most “energy-consuming” animals are small species, which is why they feed almost constantly (shrews, shrews). During the day, they consume feed 5–10 times more than their own biomass.
Ambient temperature has a significant effect on the respiratory rate. An increase in summer temperature by 10° leads to an increase in the frequency of respiration in predatory species (fox, polar bear, black bear) by 1.5–2 times.
The respiratory system plays a significant role in maintaining temperature homeostasis. Together with the exhaled air, a certain amount of water (“polyps”) and thermal energy are removed from the body. The higher the summer temperature values, 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, which emerges from the left ventricle and ends with the vena cava, which returns venous blood to the right atrium.
The unpaired innominate artery originates from the left aortic arch (Fig. 73), from which the right subclavian and paired carotid arteries depart. Each carotid artery, in turn, divides 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 a 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 organs of the body is collected in a number of vessels (Fig. 74), from which the blood merges into the common vena cava, carrying blood to the right atrium. From the front of the body, it goes along the anterior vena cava, which draws blood from the jugular veins of the head and subclavian veins extending from the forelimbs. On each side of the neck, two jugular vessels pass - the external and internal veins, which merge with the corresponding subclavian vein, forming the vena cava.
Many mammals show asymmetric development of the anterior vena cava. The innominate vein flows into the right anterior vena cava, which is formed by the confluence of the veins of the left side of the neck - the left subclavian and jugular. Characteristic of mammals is the preservation of rudiments of the posterior cardinal veins, which are called unpaired (vertebral) veins. Asymmetry is also traced in their development: the left unpaired vein connects with the right unpaired 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 the venous vessels that form the posterior vena cava are the unpaired caudal, paired femoral, iliac, renal, genital and a number of others. The posterior vena cava passes without branching through the liver, pierces the diaphragm and carries venous blood into the right atrium.
The portal system of the liver is formed by one vessel - the portal vein of the liver, resulting from the fusion of veins coming from the internal organs.
These include: splenogastric vein, anterior and posterior mesenteric veins. The portal vein forms a complex system of capillaries penetrating the liver tissue, which at the exit recombine and form short hepatic veins that flow into the posterior vena cava. The portal system of the kidneys in mammals is completely reduced.
The pulmonary circulation originates from the right ventricle, where venous blood enters from the right atrium, and ends with the left atrium. From the right ventricle, venous blood exits through the pulmonary artery, which splits into two vessels going to the lungs. Oxidized blood in the lungs enters the left atrium through the paired pulmonary veins.
The heart of different species of mammals differs in its size. Small and mobile animals have a relatively larger heart. The same pattern can be traced in relation to the frequency of contractions of the heart. So, the pulse rate in a mouse is 600 per minute, in a dog - 140, in an elephant - 24.
Hematopoiesis is carried out in different organs of mammals. Red blood cells (erythrocytes), granulocytes (neutrophils, eosinophils and basophils) and platelets are produced by the bone marrow. Erythrocytes are non-nuclear, which increases their oxygen transfer to organs and tissues, without wasting it on the processes of their own respiration. Lymphocytes are produced in the spleen, thymus, and lymph nodes. The reticuloendothelial system produces monocytic cells.
excretory system.
Water-salt metabolism in mammals is mainly carried out by the kidneys, the work of which is coordinated by pituitary hormones. A certain proportion of water-salt metabolism is performed by the skin, supplied with sweat glands, and the 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 - on the eve of the vagina.
The kidneys of mammals 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 bodies). The filtration of metabolic products comes from the blood vessels of the Malpighian bodies into the Bowman's capsules. The primary filtrate in its content is blood plasma, devoid of proteins, but containing many substances useful for the body.
An efferent tubule (nephron) departs from each Bowman's capsule. It has four sections - proximal convoluted, loop of Henle, distal convoluted and collecting duct. The system of nephrons forms lobules (pyramids) in the medulla of the kidneys, which are clearly visible on the macrosection of the organ.
In the upper (proximal) section, the nephron makes several bends, which are braided by blood capillaries. It reabsorbs (reabsorbs) water and other nutrients into the blood - sugars, amino acids and salts.
In the following departments (loop of Henle, distal convoluted) there is a further absorption of water and salts. As a result of the complex filtering work of the kidney, the end product of metabolism is formed - secondary urine, which flows down 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 passes through the human renal tubules, while only about 1–2 liters of secondary urine is formed.
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Physiology of the kidneys
The kidneys play an exceptional role in the normal functioning of the body. By removing decay products, excess water, salts, harmful substances and some drugs, the kidneys perform an excretory function.
In addition to excretory, the kidneys have other equally important functions. By removing excess water and salts from the body, mainly sodium chloride, the kidneys maintain the osmotic pressure of the internal environment of the body. Thus, the kidneys are involved 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 excrete. The kidneys also carry out a secretory function. They have the ability to secrete organic acids and bases, K+ and H+ ions. This feature 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, by regulating the osmotic pressure in the body, the constancy of the reaction of the blood, performing 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 imagine the work of the kidneys, it is necessary to get acquainted 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 recess in which there are vessels and nerves surrounded by connective tissue. The kidneys are covered with a connective tissue capsule. The dimensions of an adult kidney are about 11 10-2 × 5 10-2 m (11 × 5 cm), weight is on average 0.2-0.25 kg (200-250 g).
On a longitudinal section of the kidney, two layers are visible: cortical - dark red and cerebral - lighter (Fig. 39).
Rice. 39. The structure of the kidney. A - general structure; B - several times enlarged area of the renal tissue; 1 - Shumlyansky's capsule; 2 - convoluted tubule of the first order; 3 - loop of Henle; 4 - convoluted tubule of the second order Microscopic examination of the structure of the kidneys of mammals 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 cup, 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 body consists of the vascular glomerulus of Shumlyansky and the surrounding Bowman's capsule (Fig. 40); 2) the proximal segment includes the proximal convoluted and straight tubules; 3) 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 connecting 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 certain areas of the kidney. In the cortical layer there are vascular glomeruli, elements of the proximal and distal segments of the urinary tubules. In the medulla there are elements of a thin segment of the tubules, thick ascending limbs of the loops of Henle and collecting ducts (Fig. 41).
Rice. 41. Scheme 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 the common excretory ducts, which pass through the medulla of the kidney to the tops of the papillae, protruding into the cavity of the renal pelvis. The renal pelvis opens into the ureters, which in turn drain into the bladder.
Blood supply to the kidneys. The kidneys receive blood from the renal artery, which is one of the major branches of the aorta. The artery in the kidney is divided into a large number of small vessels - arterioles, bringing blood to the glomerulus (bringing arteriole a), which then break up into capillaries (the first network of capillaries). The capillaries of the vascular glomerulus, merging, form the efferent arteriole, the diameter of which is 2 times smaller than the diameter of the afferent. The efferent arteriole again breaks up into a network of capillaries braiding 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 braiding the renal tubules.
Arterial capillaries pass into venous capillaries, which later, merging into veins, give blood to the inferior vena cava.
The blood pressure in the capillaries of the vascular glomerulus is higher than in all the 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 surrounding the tubules of the kidney, 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 an abundant blood flow allows you to completely remove all the resulting unnecessary and even harmful substances for the body.
The lymphatic vessels of the kidneys accompany the blood vessels, forming a plexus at the hilum of the kidney that surrounds the renal artery and vein.
Innervation of the kidneys. In terms of richness of innervation, the kidneys are second only to the adrenal glands. Efferent innervation is carried out mainly due to sympathetic nerves.
Parasympathetic innervation of the kidneys is expressed slightly. A receptor apparatus was found in the kidneys, from which afferent (sensory) fibers depart, which go mainly as part of the celiac nerves.
A large number of receptors and nerve fibers were 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 in connection with 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 glomerular afferent arteriole, and cells of the so-called dense spot (macula densa) of the distal convoluted tubule.
JGA is involved in the regulation of water-salt homeostasis and maintaining a constant blood pressure. JGA cells secrete a biologically active substance - renin. Renin secretion is inversely related to the amount of blood flowing through the afferent arteriole and 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 a plasma protein, hypertensinogen. Under the influence of renin, this protein passes into its active form - hypertensin (angiotonin). Angiotonin has a vasoconstrictive effect, due to which it is a regulator of the renal and general 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 formed. It is destroyed by a special enzyme (hypertensinase). In some kidney diseases, renin secretion increases, which can lead to a persistent increase in blood pressure and a violation of water-salt metabolism in the body.
Mechanisms of urinary formation
Urine is formed from the blood plasma flowing through the kidneys and is a complex product of the activity of the 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 is filtered from the blood plasma with all inorganic and organic substances dissolved in it, which have a low molecular weight. This fluid enters the glomerular capsule (Bowman's capsule), and from there into the tubules of the kidneys. In terms of 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 of glomerular filtration in experiments on animals. He used microphysiological research methods in his work. In frogs, guinea pigs, and rats, Richards exposed the kidney and floor with a microscope into one of Bowman's capsules with the finest micropipette, with which he collected the resulting filtrate. An analysis of the composition of this fluid 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 to the pressure in the capillaries of other areas of the body is due to the fact that the renal artery departs from the aorta, and the afferent arteriole of the glomerulus is wider than the efferent one. However, the plasma in the glomerular capillaries is not filtered under all this pressure. Blood proteins retain water and thus prevent the filtration of urine. The pressure created by plasma proteins (oncotic pressure) is 3.33-4.00 kPa (25-30 mmHg). In addition, the filtration force also decreases by the pressure of the liquid in the cavity of the Bowman's capsule, which is 1.33-2.00 kPa (10-15 mm Hg).
Thus, the pressure under the influence of which primary urine is filtered 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 in the cavity of Bowman's capsule, on the other. Therefore, the value of the filtration pressure 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 a decrease in it (narrowing of the afferent vessel). The amount of filtration is also affected by the change in the permeability of the membrane through which filtration occurs. The membrane includes the endothelium of the capillaries of the glomerulus, the main (basal) membrane and the cells of the inner layer of the Bowman's capsule.
tubular reabsorption. Reabsorption (reabsorption) from the primary urine into the blood of water, glucose / part of the salts and a small amount of urea occurs in the renal tubules. As a result of this process, the final, or secondary, urine is formed, which differs sharply from the primary in its composition. It does not contain glucose, amino acids, some salts, and the concentration of urea is sharply increased (Table 11).
Table 11. The content 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 reverse absorption in the tubules of water and many substances dissolved in it, only 1-1.5 liters of final urine is excreted by the kidneys 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, sodium salts are actively reabsorbed. These substances are completely absorbed in the tubules and are absent in the final urine. Due to active reabsorption, the reverse absorption of substances from the urine into the blood is also possible even when their concentration in the blood is equal to the concentration in the liquid of the tubules or higher.
Passive reabsorption occurs without energy expenditure due to diffusion and osmosis. A large role in this process belongs to the difference between oncotic and hydrostatic pressure in the tubule capillaries. Due to passive reabsorption, water, chlorides, and urea are reabsorbed. Removed substances pass through the wall of the tubules only when their concentration in the lumen reaches a certain threshold value. Substances to be excreted from the body undergo passive reabsorption. They are always found in urine. The most important substance of this group is the end product of nitrogen metabolism - urea, which is reabsorbed in small quantities.
The reverse absorption of substances from urine into the blood in different parts of the nephron is not the same. So, 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. A special place in the mechanism of reabsorption of water and sodium ions is occupied by the loop of Henle due to the so-called turn-countercurrent system. Let's consider its essence. The loop of Henle has two limbs: descending and ascending. The epithelium of the descending section is permeable to water, and the epithelium of the ascending knee is not permeable to water, but is able to actively absorb sodium ions and transfer them into the tissue fluid, and through it back into the blood (Fig. 42).
Rice. 42. Scheme of operation of the rotary-countercurrent system (according to Best and Taylor). The darkened background shows the value of the concentration of urine and tissue fluid. White arrows - water release, black arrows - sodium ions; 1 - convoluted tubule, passing into the proximal loop; 2 - convoluted tubule emerging from the distal loop; 3 - collecting tube Passing through the descending loop of Henle, urine gives off water, thickens, becomes more concentrated. The release of water occurs passively due to the fact that at the same time in the ascending section, active reabsorption of sodium ions is carried out. Entering the tissue fluid, sodium ions increase the osmotic pressure in it and thereby contribute to the attraction of water from the descending knee into the tissue fluid. In turn, an increase in the concentration of urine in the loop of Henle due to the reabsorption of water facilitates the transition of sodium ions from the urine into the tissue fluid. Thus, large amounts of water and sodium ions are reabsorbed in the loop of Henle.
In the distal convoluted tubules, further absorption of sodium, potassium, water and other substances is carried out. Unlike the proximal convoluted tubules and the loop of Henle, where the reabsorption of sodium and potassium ions does not depend on their concentration (mandatory reabsorption), the reabsorption of these ions in the distal tubules is variable and depends on their level in the blood (facultative reabsorption). Consequently, the distal convoluted tubules regulate and maintain a constant concentration of sodium and potassium ions in the body.
In addition to reabsorption, the process of secretion is carried out in the tubules. With the participation of special enzyme systems, there is an active transport of certain substances from the blood into the lumen of the tubules. Of the products of protein metabolism, active secretion undergoes creatinine, paraaminohippuric acid. In full force, this process is manifested when foreign substances 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 organism, these systems can change the direction of the active transfer of substances, that is, they provide either their secretion (excretion) or reabsorption.
In addition to filtering, reabsorbing and secreting, the cells of the renal tubules are able to synthesize certain substances from various organic and inorganic products. So, in the cells of the renal tubules, hippuric acid (from benzoic acid and glycocol), ammonia (by deamination of some amino acids) are synthesized. The synthetic activity of the tubules is also carried out with the participation of enzyme systems.
The function of the collecting ducts. Further absorption of water takes place 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 to itself.
Thus, urination 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 proceeds mainly due to the energy of blood pressure, i.e., ultimately due to the functioning of the cardiovascular system, then the processes of reabsorption, secretion and synthesis are the result of the activity of tubular cells and require energy expenditure. As a result, the kidneys need more 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 (due to changes in the lumen of the 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 decreases, and, consequently, the filtration of primary urine also decreases. Transection of the sciatic nerve leads to an increase in urine output by 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 the blood pressure decreases and the intensity of diuresis changes; 2) regulating the lumen of the vessels of the kidneys.
With painful stimuli, diuresis decreases reflexively until its complete cessation (painful anuria). This is due to the fact that there is a narrowing of the renal vessels due to the excitation 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 work. Bilateral transection of nerves causes a violation of metabolic processes in the kidneys and a sharp decrease in their functional activity. A denervated kidney cannot quickly and subtly reorganize its activity and adapt to changes in the level of water-salt load. After the introduction of 1 liter of water into the animal's stomach, the increase in diuresis in the denervated kidney occurs later than in the healthy one.
In the laboratory of K. M. Bykov, by developing 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 work 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 due to 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 urination and an increase in the osmotic concentration of urine. With an excess of vasopressin, complete cessation of urination (anuria) can occur. The lack of this hormone in the blood leads to the development of a serious disease - diabetes insipidus. With this disease, a large amount of light urine with a low relative density is excreted, in which there is no sugar.
Aldosterone (hormone of the adrenal cortex) promotes the reabsorption of sodium ions and the excretion of potassium ions in the distal tubules and inhibits the reabsorption of calcium and magnesium in their proximal sections.
Quantity, composition and properties of urine
During the day, a person allocates an average of about 1.5 liters of urine, but this amount is not constant. So, for example, diuresis increases after heavy drinking, consumption of protein, the breakdown products of which stimulate urine formation. On the contrary, urination decreases with the consumption of a small amount of water, protein, with increased sweating, when a significant amount of fluid is excreted with sweat.
The intensity of urination fluctuates throughout the day. More urine is produced during the day than at night. Decreased urination at night is associated with a decrease in body activity during sleep, with a slight drop in blood pressure. Night urine is darker and more concentrated.
Physical activity has a pronounced effect on the formation of urine. With prolonged work, there is a decrease in the excretion of urine from the body. This is due to the fact that with increased physical activity, more blood flows 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 settling in the urine, a precipitate forms, which consists of salts and mucus.
urine reaction. The reaction of the urine of a healthy person is predominantly slightly acidic, its pH ranges from 4.5 to 8.0. The reaction of urine may vary depending on the diet. When eating mixed food (animal and vegetable origin), human urine has a slightly acidic reaction. When eating mainly meat food and other foods rich in proteins, the urine reaction becomes acidic; vegetable food contributes 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.
The composition of urine. The kidneys are the main organ for excretion of nitrogenous protein breakdown products - urea, uric acid, ammonia, purine bases, creatinine, indican - from the body.
Urea is the main product of protein breakdown. Up to 90% of all urine nitrogen is urea. In normal urine, protein is absent or only its traces are determined (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 vascular glomerulus of the kidneys.
Among the organic compounds of non-protein origin in the urine there are: oxalic acid salts that enter the body with food, especially vegetable; lactic acid released after muscle activity; ketone bodies formed when fats are converted into sugar in the body.
Glucose appears in the urine only when its content in the blood is sharply increased (hyperglycemia). The excretion of sugar in the urine is called glycosuria.
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 its yellow color depends. These pigments are formed from bile bilirubin in the intestines and kidneys and are excreted 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 acid reaction of urine also depends on them (Table 12).
Table 12. The amount of substances that make up the urine (excreted in 24 hours) Excretion of urine. The final urine flows from the tubules to the pelvis and from it to the ureter. The movement of urine through the ureters to the bladder is carried out under the influence of gravity, as well as due to the peristaltic movements of the ureters. The ureters, obliquely entering the bladder, 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 excreted from the body through the act of urination.
In the bladder there are so-called sphincters, or sphincter (annular muscle bundles). They tightly close the exit from the bladder. The first of the sphincters - the sphincter of the bladder - is located at its exit. The second sphincter - the sphincter of the urethra - is located slightly below 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 an increase in the tone of its sphincters. Thus, the excitation of the sympathetic nerves contributes to the accumulation of urine in the bladder. When the parasympathetic fibers are stimulated, the bladder wall contracts, the sphincters relax, and urine is expelled from the bladder.
Urine continuously flows into the bladder, which leads to an increase in pressure in it. An increase in pressure in the bladder up to 1.177-1.471 Pa (12-15 cm of water column) causes the need to urinate. After the act of urination, the pressure in the bladder decreases to almost 0.
Urination is a complex reflex act, consisting in the 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 appearance of nerve impulses in the mechanoreceptors of this organ. Afferent impulses enter the 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. There is a reflex contraction of its muscular wall and relaxation of the sphincter. Simultaneously, from the center of urination, excitation is transmitted to the cerebral cortex, where there is a sensation of the urge to urinate. Impulses from the cerebral cortex through the spinal cord arrive at the sphincter of the urethra. There comes the act of urination. Cortical control manifests itself in delay, intensification or even voluntary induction of urination. In young children, there is no cortical control of urinary retention. It develops gradually with age.
2.1 Examination of the kidneys
In cattle, the kidneys are of the striated or multipapillary type. On rectal palpation, separate lobules are felt. In pigs, the kidneys are smooth, multi-papillary; in horses, small cattle, deer, dogs, and cats, they are almost smooth. The topography of the kidneys in animals of different species has features.
Examining the kidneys, they examine the animal, palpation and percussion of the kidneys, radiological and functional studies. Of particular importance is the laboratory study of urine.
Inspection. Kidney damage is accompanied by depression, immobility of animals. Diarrhea, hypotension and atony of the proventriculus are possible, in carnivores - vomiting and convulsions. With chronic kidney disease, exhaustion, itching, baldness, matte coat occurs. Small white scales of urea appear on the surface of the skin. Of particular importance is the appearance of renal (“flying”) edema. There may be dropsy of the serous cavities. 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 in large quantities sweats into the tissue. The cause of such edema may be an increase in blood pressure.
Edema in acute renal failure is formed against the background of uremia.
PalpaqiI am allows you to determine the position, shape, size, mobility, consistency, tuberosity and sensitivity of the kidneys during external and rectal examinations.
In cattle, external (with low fatness) and internal palpation are performed. Outside, 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 3-5th lumbar vertebrae, is mobile, hangs 10-12 cm from the spine. In small cows, you can feel the caudal edge of the right kidney, which is located under the transverse processes of the vertebrae from the last intercostal space to the 2-3rd lumbar on the right. It is well fixed on a 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 vertebra. In large horses, only the caudal edge of the left kidney can be felt. In small animals, the medial and lateral surfaces of the kidneys, the renal pelvis, and the renal artery (by pulsation) can be palpated.
In pigs, external palpation of the kidneys is possible only in malnourished individuals. The kidneys are located under the transverse processes of the 1st-4th lumbar vertebrae.
In sheep and goats, the kidneys are accessible for 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 under the 1st-3rd. Their surface is smooth. They move a little on 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 be palpated only partially, under the 1st-3rd lumbar vertebrae it is possible to feel its caudal edge.
An increase in the kidneys can be caused by paranephritis, pyelonephritis, hydronephrosis, nephrosis, amyloidosis. A decrease in the kidneys is noted in chronic processes - chronic nephritis and pyelonephritis, cirrhosis. Changes in the surface of the kidneys (tuberosity) may be the result of tuberculosis, echinococcosis, leukemia, tumors, abscesses, chronic lesions (nephritis, pyelonephritis). Soreness of the kidneys is noted with glomerulo-, pyelo- and paranephritis, as well as with urolithiasis. When applying sharp, gentle blows to the kidney area, pain occurs.
Percussion. In large animals, the kidneys are percussed with a mallet and a plessimeter, in small animals, digitally. Kidneys in healthy animals are not detected by percussion, since they are not adjacent to the abdominal wall. In sick animals with a sharp increase in the kidneys (paranephritis, pyelonephritis, hydronephrosis), this method can establish a dull sound at the location of the kidneys.
In large animals, the tapping method is used: the palm of the left hand is pressed against the lower back in the area of the projection of the kidneys, and short, mild blows are applied with the fist of the right hand.
In healthy animals, no signs of pain are found during effleurage; soreness is noted in the case of paranephritis, inflammation of the kidneys and renal pelvis, with urolithiasis.
Biopsy. This method is rarely used for diagnostic purposes. A piece of kidney tissue is taken through the skin using a special needle with a syringe or a soft tissue biopsy trocar. 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 bacteriologically - determine the microflora in the tissues of the kidneys.
X-ray examination is of great importance in small animals for the detection of stones and tumors in the urinary system, cysticity, hydronephrosis, nephritis, edema. An increase in the shadow of only one kidney is possible with hydronephrosis, the presence of a tumor.
Functional Research kidneys are reduced to the determination in the blood of substances secreted by the kidneys (residual nitrogen, uric acid, creatinine, etc.), the ability of the kidneys to concentrate and dilute urine, the study of the excretory function of the kidneys after exercise, as well as the cleansing function (clearance) of the kidneys.
Functional Research. They include determining the amount of urine excreted and its relative density; a test with indigo carmine (modified by K. K. Movsum-Zade) is also used.
Test according to Zimnitsky: the animal is kept on a normal diet for 1 day, water supply is not limited. Urine samples are collected in a urinal during natural urination, the amount of urine, its relative density, sodium chloride content are determined. The wider the boundaries of controlled parameters, the better preserved kidney function. In cattle, the normal total diuresis in relation to the drunk water is 23.1%, the chloride content is 0.475%. With functional kidney failure, nocturnal diuresis (nocturia) predominates, and with significant insufficiency, a decrease in the relative density of urine is noted - hypostenuria, often combined with polyuria.
Test with a load of water: the animal in the morning on an empty stomach after emptying the bladder is injected through a nasopharyngeal probe with tap water at room temperature. 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 from the diet is excluded until the next day. During the test, urine is collected in a urinal 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), in 4 ... 6 hours from the start of the experiment, 33 ... days - 10 ... 23%. The total diuresis is 48.5...76.7%. An increase in the excretion of water by the kidneys during a water load in sick animals reflects tubular insufficiency, and water retention in the body reflects glomerular insufficiency.
Concentration test: the animal is kept without water for 24 hours. Urine is collected during an arbitrary act of urination and its relative density is determined. Normally, in cattle on the day of the start of the experiment, a decrease in urination is noted up to 1...4 times, diuresis decreases to 1...4 l, the relative density of urine increases by 8...19 divisions. With tubular insufficiency 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 a few milliliters of urine are taken into a test tube for control. After that, the cow is infused intravenously with a 4% solution of indigo carmine at a dose of 20 ml and urine samples are taken through the 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 ... And min. Urine coloration becomes more intense in the range 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 are found in the urine. The release of the dye is disturbed in disorders of kidney function, renal blood flow, outflow of urine from the renal pelvis and ureters.
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