Wonderful capillary network. Rectum

A person who has been at a depth of more than 20 m for a long time is threatened with decompression sickness upon ascent. At depth, under high pressure, air nitrogen dissolves in the blood. With a sharp rise, the pressure drops, the solubility of nitrogen decreases, and gas bubbles form in the blood and tissues. They clog small blood vessels, cause severe pain, and in the central nervous system, their release can lead to death, so special safety measures have been developed for divers and divers: they ascend very slowly or breathe special gas mixtures that do not contain nitrogen.

How do animals that constantly dive (seals, penguins, whales) avoid decompression sickness? Physiologists have been interested in this question for a long time, and they, of course, found explanations: penguins dive for a short time, seals exhale before diving, in whales, air at depth is squeezed out of the lungs into a large incompressible trachea. And if there is no air in the lungs, then nitrogen does not enter the blood. Another explanation for the absence of decompression sickness in whales was recently proposed by specialists from the University of Tromsø ( University of Tromsø) and the University of Oslo ( University of Oslo). According to scientists, whales are protected by an extensive network of thin-walled arteries that supply blood to the brain.

This vast vascular network, which occupies a significant part of the chest, penetrates the spine, neck region and base of the head of cetaceans, was first described in 1680 by the English anatomist Edward Tyson in his work “Anatomy of a harbor porpoise, opened at Gresham College; with a preliminary discussion of the anatomy and natural history of animals", and called it a wonderful network - retia mirabilia. Subsequently, this network was described by different scientists in different species, including the bottlenose dolphin. Tursiops truncates, narwhal Monodon monoceros, belugas Delphinapterus leucas and sperm whale Physeter macrocephalus. Researchers have come up with various hypotheses about the functions of the miraculous network, the most popular being that it regulates blood pressure.

Norwegian scientists return to Tyson's object, the porpoise Phocoena phocoena. They got two medium-sized females - 32 and 36 kg, killed by fishermen during industrial fishing in the Lofoten Islands. Detailed study of the thoracic region retia mirabilia showed that relatively thick arteries, forming a network visible to the naked eye, are divided into many tiny vessels that communicate with each other through thin-walled sinuses. These vascular structures are recessed into adipose tissue. It is through this network that blood enters the brain.

There are few muscle cells in the walls of the arteries of the network, and they are not innervated, that is, the lumen of the vessels is always constant. But the researchers note that it does not need to be regulated, since the brain needs a constant amount of blood.

The total cross-sectional area of ​​all vessels and vessels is so large that the rate of blood flow in the network drops to almost zero, which significantly increases the possibility of exchange between blood and surrounding adipose tissue through the vascular wall. The researchers hypothesized that in diving cetaceans, nitrogen from supersaturated blood diffuses into fat, in which it is six times more soluble than in water. So diffusion in retia mirabilia prevents the formation of nitrogen bubbles that can reach the brain and cause decompression sickness.

Among the works cited by Norwegian researchers, there is also an article by a leading researcher at the Pacific Oceanological Institute. V. I. Ilyichev FEB RAS Vladimir Vasilievich Melnikov, who in 1997 dissected the sperm whale. He writes that retia mirabilia in the sperm whale it is more developed than in other cetaceans (of course, those that have been dissected). But it is the sperm whale that is the champion among cetaceans in terms of depth and duration of diving. Perhaps this fact indirectly confirms the hypothesis of Norwegian scientists.

Photo from article: Arnoldus Schytte Blix, Lars Walløe and Edward B. Messelt. On how whales avoid decompression sickness and why they sometimes strand // J. Exp Biol, 2013, doi:10.1242/jeb.087577.

The kidneys are located in the lumbar region (region lumbalis) on both sides of the spinal column, on the inner surface of the posterior abdominal wall and lie retroperitoneally (retroperitoneally).

The left kidney is slightly higher than the right.

The upper end of the left kidney is at the level of the middle XI thoracic vertebra, and the upper end of the right kidney corresponds to the lower edge of this vertebra.

The lower end of the left kidney lies at the level of the upper edge III lumbar vertebra, and the lower end of the right kidney is at the level of its middle.

Vessels and nerves of the kidney

The bloodstream of the kidney is represented by arterial and venous vessels and capillaries.

Blood enters the kidney through the renal artery (a branch of the abdominal aorta), which divides into the anterior and posterior branches at the hilum of the kidney. In the renal sinus, the anterior and posterior branches of the renal artery pass anterior and posterior to the renal pelvis and divide into segmental arteries.

The anterior branch gives off four segmental arteries: to the superior, superior anterior, inferior anterior, and inferior segments. The posterior branch of the renal artery continues into the posterior segment of an organ called the posterior segmental artery. The segmental arteries of the kidney branch into the interlobar arteries, which run between adjacent renal pyramids in the renal columns.

At the border of the medulla and cortex, the interlobar arteries branch and form arcuate arteries.

Numerous interlobular arteries depart from the arcuate arteries into the cortex, giving rise to the afferent glomerular arterioles. Each afferent glomerular arteriole (afferent vessel) arteriola glomerularis afferens, breaks up into capillaries, the loops of which form glomerulus,glomerulus.

The efferent glomerular arteriole emerges from the glomerulus arteriola glomerularis efferens.

After leaving the glomerulus, the efferent glomerular arteriole breaks up into capillaries that braid the renal tubules, forming a capillary network of the cortical and medulla of the kidney.

miraculous kidney network

This branching of the afferent arterial vessel into the capillaries of the glomerulus and the formation of the efferent arterial vessel from the capillaries is called wonderful network, rete mirabile. In the medulla of the kidney from the arcuate and interlobar arteries and from some of the efferent glomerular arterioles, direct arterioles depart, supplying the renal pyramids.

Arc veins

From the capillary network of the cortical substance of the kidney, venules are formed, which, merging, form interlobular veins that flow into arcuate veins, located on the border of the cortex and medulla. The venous vessels of the medulla of the kidney also flow here. In the most superficial layers of the cortical substance of the kidney and in the fibrous capsule, the so-called stellate venules are formed, which flow into the arcuate veins. They, in turn, pass into the interlobar veins, which enter the renal sinus, merge with each other into larger veins that form the renal vein. The renal vein exits the hilum of the kidney and empties into the inferior vena cava

The kidneys are located retroperitoneally (retroperitoneally) on both sides of the spine, with the right kidney slightly lower than the left. The lower pole of the left kidney lies at the level of the upper edge of the body of the third lumbar vertebra, and the lower pole of the right kidney corresponds to its middle. The XII rib crosses the posterior surface of the left kidney almost in the middle of its length, and the right one - closer to its upper edge.

The kidneys are bean-shaped. The length of each kidney is 10-12 cm, width - 5-6 cm, thickness - 3-4 cm. The mass of the kidney is 150-160 g. The surface of the kidneys is smooth. In the middle section of the kidney there is a recess - the renal gate (hilus renalis), into which the renal artery and nerves flow. The renal vein and lymphatic ducts emerge from the renal hilum. Here is the renal pelvis, which passes into the ureter.

On the section of the kidney, 2 layers are clearly visible: the cortical and medulla of the kidney. In the tissue of the cortical substance there are renal (Malpighian) bodies. In many places, the cortical substance penetrates deeply into the thickness of the medulla in the form of radially located renal columns, which divide the medulla into renal pyramids, consisting of straight tubules forming a nephron loop, and collecting ducts passing through the medulla. The tops of each renal pyramid form the renal papillae, with openings opening into the renal calyces. The latter merge and form the renal pelvis, which then passes into the ureter. The renal calyces, pelvis and ureter make up the urinary tract of the kidney. From above, the kidney is covered with a dense connective tissue capsule.

The bladder is located in the pelvic cavity and lies behind the pubic symphysis. When filling the bladder with urine, its tip protrudes above the pubis and comes into contact with the anterior abdominal wall. In women, the posterior surface of the bladder is in contact with the anterior wall of the cervix and vagina, while in men it is adjacent to the rectum.

The female urethra is short - 2.5–3.5 cm long. The length of the male urethra is about 16 cm; its initial (prostate) part passes through the prostate gland.

The main feature of the blood supply to the renal (cortical) nephron is that the interlobular arteries split twice into arterial capillaries. This is the so-called "miraculous network" of the kidney. The afferent arteriole, after entering the glomerular capsule, breaks up into glomerular capillaries, which then unite again and form the efferent glomerular arteriole. The latter, after leaving the Shumlyansky-Bowman capsule, again breaks up into capillaries, densely braiding the proximal and distal sections of the tubules, as well as the loop of Henle, providing them with blood.

The second important feature of blood circulation in the kidney is the existence of two circles of blood circulation in the kidneys: large (cortical) and small (juxtamedullary), corresponding to two types of nephrons of the same name.

The glomeruli of juxtamedullary nephrons are also located in the renal cortex, but somewhat closer to the medulla. The loops of Henle of these nephrons descend deep into the renal medulla, reaching the tops of the pyramids. The efferent arteriole of the juxtamedullary nephrons does not split into a second capillary network, but forms several direct arterial vessels that go to the tops of the pyramids, and then, forming a turn in the form of a loop, return back to the cortical substance in the form of venous vessels. Direct vessels of the juxtamedullary nephrons, located near the ascending and descending parts of the loop of Henle and being essential elements of the countercurrent-turning system of the kidneys, play an important role in the processes of osmotic concentration and dilution of urine.

The kidneys are the main excretory organ. They perform many functions in the body. Some of them are directly or indirectly related to the extraction processes, while others do not have such a connection.

A person has a pair of kidneys lying at the back of the abdominal cavity on both sides of the spine at the level of the lumbar vertebrae. The weight of one kidney is about 0.5% of the total body weight, the left kidney is slightly advanced compared to the right kidney.

Blood enters the kidneys through the renal arteries, and flows out of them through the renal veins, which empty into the inferior vena cava. The urine formed in the kidneys flows down the two ureters to the bladder, where it accumulates until it is excreted through the urethra.

On the transverse section of the kidney, two clearly distinguishable zones are visible: the cortical substance of the kidney lying closer to the surface and the inner medulla of the kidney. The renal cortex is covered with a fibrous capsule and contains renal glomeruli, barely visible to the naked eye. The medulla is made up of renal tubules, renal collecting ducts, and blood vessels, assembled together to form renal pyramids. The tops of the pyramids, called the renal papillae, open into the renal pelvis, which forms an enlarged orifice of the ureter. Many vessels pass through the kidneys, forming a dense capillary network.

The main structural and functional unit of the kidney is the nephron with its blood vessels (Fig. 1.1).

The nephron is the structural and functional unit of the kidney. In humans, each kidney contains about a million nephrons, each about 3 cm long.

Each nephron includes six sections that differ greatly in structure and physiological functions: the renal corpuscle (Malpighian corpuscle), consisting of the Bowman's capsule and the renal glomerulus; proximal convoluted renal tubule; descending limb of the loop of Henle; ascending limb of the loop of Henle; distal convoluted renal tubule; collecting duct.

There are two types of nephrons - cortical nephrons and juxtamedullary nephrons. Cortical nephrons are located in the renal cortex and have relatively short loops of Henle that extend only a short distance into the renal medulla. Cortical nephrons control the volume of blood plasma with a normal amount of water in the body, and with a lack of water, its increased reabsorption in juxtamedullary nephrons occurs. In the juxtamedullary nephrons, the renal corpuscles are located near the border of the renal cortex and renal medulla. They have long descending and ascending limbs of the loop of Henle, penetrating deep into the medulla. Juxtamedullary nephrons intensively reabsorb water when there is a lack of it in the body.

Blood enters the kidney through the renal artery, which branches first into the interlobar arteries, then into the arcuate arteries and interlobular arteries, the afferent arterioles supplying blood to the glomeruli depart from the latter. From the glomeruli, the blood, the volume of which has decreased, flows through the efferent arterioles. Further, it flows through a network of peritubular capillaries located in the renal cortex and surrounding the proximal and distal convoluted tubules of all nephrons and the loop of Henle of the cortical nephrons. From these capillaries depart the renal direct vessels, running in the renal medulla parallel to the loops of Henle and collecting ducts. The function of both vascular systems is the return of blood, which contains nutrients valuable for the body, to the general circulatory system. Much less blood flows through the direct vessels than through the peritubular capillaries, due to which the high osmotic pressure necessary for the formation of concentrated urine is maintained in the interstitial space of the renal medulla.

Vessels are straight. The narrow descending and wider ascending renal capillaries of the rectus vessels run parallel to each other throughout their length and form branching loops at different levels. These capillaries pass very close to the tubules of the loop of Henle, but there is no direct transfer of substances from the loop filtrate to the direct vessels. Instead, the solutes exit first into the interstitial spaces of the renal medulla, where urea and sodium chloride are retained due to the low blood flow velocity in the direct vessels, and the osmotic gradient of the tissue fluid is maintained. The cells of the walls of the straight vessels freely pass water, urea and salts, and since these vessels run side by side, they function as a system of countercurrent exchange. When the descending capillary enters the medulla from the blood plasma, due to a progressive increase in the osmotic pressure of the tissue fluid, water leaves by osmosis, and sodium chloride and urea enter back by diffusion. In the ascending capillary, the reverse process occurs. Due to this mechanism, the osmotic concentration of plasma leaving the kidneys remains stable regardless of the concentration of plasma entering them.

Since all movements of solutes and water occur passively, countercurrent exchange in straight vessels occurs without energy expenditure.

The convoluted proximal tubule. The proximal convoluted tubule is the longest (14 mm) and widest (60 μm) part of the nephron, through which the filtrate enters the loop of Henle from the Bowman's capsule. The walls of this tubule consist of a single layer of epithelial cells with numerous long (1 μm) microvilli forming a brush border on the inner surface of the tubule. The outer membrane of the epithelial cell is adjacent to the basement membrane, and its invaginations form the basal labyrinth. The membranes of neighboring epithelial cells are separated by intercellular spaces, and fluid circulates through them and the labyrinth. This fluid bathes the cells of the proximal convoluted tubules and the surrounding network of peritubular capillaries, forming a link between them. In the cells of the proximal convoluted tubule, numerous mitochondria are concentrated near the basement membrane, generating ATP, which is necessary for the active transport of substances.

The large surface of the proximal convoluted tubules, numerous mitochondria in them, and the proximity of the peritubular capillaries are all adaptations for the selective reabsorption of substances from the glomerular filtrate. Here more than 80% of substances are absorbed back, including all glucose, all amino acids, vitamins and hormones, and about 85% of sodium chloride and water. About 50% of the urea is also reabsorbed from the filtrate by diffusion, which enters the peritubular capillaries and thus returns to the general circulatory system, the rest of the urea is excreted in the urine.

Proteins with a molecular weight of less than 68,000 entering the lumen of the renal tubule during ultrafiltration are removed from the filtrate by pinocytosis at the base of the microvilli. They find themselves inside pinocytic vesicles, to which primary lysosomes are attached, in which hydrolytic enzymes break down proteins into amino acids, which are used by tubular cells or pass by diffusion into peritubular capillaries.

In the proximal convoluted tubules, the secretion of creatinine and the secretion of foreign substances also occur, which are transported from the intercellular fluid washing the tubules into the tubular filtrate and excreted in the urine.

The convoluted distal tubule. The distal convoluted tubule approaches the Malpighian body and lies entirely in the renal cortex. The cells of the distal tubules are brush-bordered and contain many mitochondria. It is this section of the nephron that is responsible for the fine regulation of the water-salt balance and the regulation of blood pH. The permeability of the cells of the distal convoluted tubule is regulated by antidiuretic hormone.

Collecting tube. The collecting duct originates in the renal cortex from the renal distal convoluted tubule and descends through the renal medulla, where it joins with several other collecting ducts to form larger ducts (Bellini's ducts). The permeability of the walls of the collecting ducts for water and urea is regulated by antidiuretic hormone, and thanks to this regulation, the collecting duct participates, together with the distal convoluted tubule, in the formation of hypertonic urine, depending on the body's need for water.

Loop of Henle. The loop of Henle, together with the capillaries of the renal rectus vessels and the renal collecting duct, creates and maintains a longitudinal gradient of osmotic pressure in the renal medulla in the direction from the renal cortex to the renal papilla by increasing the concentration of sodium chloride and urea. Due to this gradient, more and more water can be removed by osmosis from the lumen of the tubule into the interstitial space of the renal medulla, from where it passes into the direct renal vessels. Ultimately, hypertonic urine is formed in the renal tubing. The movement of ions, urea, and water between the loop of Henle, the rectus vessels, and the collecting duct can be described as follows:

The short and relatively wide (30 µm) upper segment of the descending limb of the loop of Henle is impervious to salts, urea, and water. In this area, the filtrate passes from the proximal convoluted renal tubule to a longer thin (12 μm) segment of the descending limb of the loop of Henle, which freely passes water.

Due to the high concentration of sodium chloride and urea in the tissue fluid of the renal medulla, a high osmotic pressure is created, water is sucked out of the filtrate and enters the renal direct vessels.

As a result of the release of water from the filtrate, its volume decreases by 5% and it becomes hypertonic. At the apex of the medulla (in the renal papilla), the descending limb of the loop of Henle bends and passes into the ascending limb, which is permeable to water along its entire length.

The lower section of the ascending knee - a thin segment - is permeable to sodium chloride and urea, and sodium chloride diffuses out of it, and urea diffuses inward.

In the next thick segment of the ascending genu, the epithelium consists of flattened cuboidal cells with a rudimentary brush border and numerous mitochondria. In these cells, there is an active transfer of sodium and chloride ions from the filtrate.

Due to the release of sodium and chloride ions from the filtrate, the osmolarity of the renal medulla increases, and a hypotonic filtrate enters the distal convoluted renal tubules. Epithelial cells that perform a barrier function (mainly) epithelial cells of the genitourinary tract that perform a barrier function.

The glomerulus is renal. The renal glomerulus consists of approximately 50 capillaries collected in a bundle, into which the only afferent arteriole approaching the glomerulus branches and which then merge into the efferent arteriole.

As a result of ultrafiltration occurring in the glomeruli, all substances with a molecular weight of less than 68,000 are removed from the blood, and a fluid is formed, called glomerular filtrate.

Malpighian body. Malpighian body - the initial section of the nephron, it consists of the renal glomerulus and Bowman's capsule. This capsule is formed as a result of the invagination of the blind end of the epithelial tubule and covers the renal glomerulus in the form of a two-layer sac. The structure of the Malpighian body is entirely related to its function - blood filtration. The walls of the capillaries consist of a single layer of endothelial cells, between which there are pores with a diameter of 50 - 100 nm. These cells lie on a basement membrane that completely surrounds each capillary and forms a continuous layer that completely separates the blood in the capillary from the lumen of the Bowman's capsule. The inner layer of the Bowman's capsule is made up of cells with processes called podocytes. The processes support the basement membrane and the capillary surrounded by it. The cells of the outer leaf of the Bowman's capsule are squamous non-specialized epithelial cells.

As a result of ultrafiltration occurring in the glomeruli, all substances with a molecular weight of less than 68,000 are removed from the blood and a liquid is formed, called glomerular filtrate.

In total, 1,200 ml of blood passes through both kidneys in 1 minute (i.e., all the blood in the circulatory system passes in 4-5 minutes). This volume of blood contains 700 ml of plasma, of which 125 ml is filtered in the Malpighian bodies. Substances filtered from the blood in the glomerular capillaries pass through their pores and the basement membrane under the action of pressure in the capillaries, which can vary with a change in the diameter of the afferent and efferent arterioles, which are under nervous and hormonal control. The narrowing of the efferent arteriole leads to a decrease in the outflow of blood from the glomerulus and an increase in hydrostatic pressure in it. In this state, substances with a molecular weight of more than 68,000 can pass into the glomerular filtrate.

The chemical composition of the glomerular filtrate is similar to blood plasma. It contains glucose, amino acids, vitamins, certain hormones, urea, uric acid, creatinine, electrolytes, and water. Leukocytes, erythrocytes, platelets and plasma proteins such as albumin and globulins cannot leave the capillaries - they are retained by the basement membrane, which acts as a filter. The blood flowing from the glomeruli has an increased oncotic pressure, since the concentration of proteins in the plasma is increased, but its hydrostatic pressure is reduced.

Renal circulation. The average rate of renal blood flow at rest is about 4.0 ml / g per minute, i.e. in general, for kidneys weighing about 300 g, about 1200 ml per minute. This represents approximately 20% of total cardiac output. The peculiarity of the renal circulation is the presence of two successive capillary networks. The afferent arterioles break up into the glomerular capillaries of the kidneys, separated from the peritubular capillary bed of the kidneys by the efferent arterioles. The efferent arterioles are characterized by high hydrodynamic resistance. The pressure in the glomerular capillaries of the kidneys is quite high (about 60 mm Hg), and the pressure in the peritubular capillaries of the kidneys is relatively low (about 13 mm Hg).

On a longitudinal section through the kidney, it can be seen that the kidney as a whole is composed, firstly, from the cavity, sinus renalis, in which the renal cups and the upper part of the pelvis are located, and, secondly, from the renal substance itself, adjacent to the sinus on all sides, with the exception of the gate. In the kidney, a cortical substance is distinguished, cortex renis, and the medulla medulla renis.

cortex occupies the peripheral layer of the organ, has a thickness of about 4 mm. The medulla is composed of conical-shaped formations called renal pyramids, pyramides renales. The broad bases of the pyramids face the surface of the organ, and the tops face the sinus.

The tops are connected in two or more rounded elevations, called papillae, papillae renales; less often one apex corresponds to a separate papilla. There are an average of 12 papillae in total.

Each papilla is dotted with small holes, foramina papillaria; across foramina papillaria urine is excreted in the initial parts of the urinary tract (cups). The cortical substance penetrates between the pyramids, separating them from each other; these parts of the cortex are called columnae renales. Due to the urinary tubules and vessels located in them in the forward direction, the pyramids have a striped appearance. The presence of pyramids reflects the lobular structure of the kidney, which is characteristic of most animals.

The newborn retains traces of the former division even on the outer surface, on which furrows are visible (lobular kidney of the fetus and newborn). In an adult, the kidney becomes smooth on the outside, but inside, although several pyramids merge into one papilla (which explains the smaller number of papillae than the number of pyramids), it remains divided into slices - pyramids.

Strips of medullary substance also continue into the cortical substance, although they are less clearly visible here; they make up pars radiata cortical substance, the gaps between them - pars convoluta(convolutum - bundle).
Pars radiata and pars convoluta united under the name lobulus corticalis.

The kidney is a complex excretory (excretory) organ. It contains tubes called renal tubules, tubuli renales. The blind ends of these tubules in the form of a double-walled capsule cover the glomeruli of blood capillaries.

Each glomerulus, glomerulus, lies in deep cup-shaped capsule, capsula glomeruli; the gap between the two leaves of the capsule is the cavity of this latter, being the beginning of the urinary tubule. Glomerulus together with the enclosing capsule is renal corpuscle, corpusculum renis.

The renal corpuscles are located in pars convoluta cortex, where they can be seen with the naked eye as red dots. A convoluted tubule arises from the renal corpuscle tubulus renalis contdrtus, which is already in the pars radiata of the cortex. Then the tubule descends into the pyramid, turns back there, making a loop of the nephron, and returns to the cortical substance.

The final part of the renal tubule - the intercalary section - flows into the collecting duct, which receives several tubules and goes in a straight direction (tubulus renalis rectus) through pars radiata of the cortex and through the pyramid. Straight tubules gradually merge with each other and in the form of 15 - 20 short ducts, ductus papillares, open foramina papillaria in the region of area cribrosa at the top of the papilla.

renal corpuscle and the tubules related to it constitute the structural and functional unit of the kidney - nephron, nephron. Urine is produced in the nephron. This process takes place in two stages: in the renal body, the liquid part of the blood is filtered from the capillary glomerulus into the cavity of the capsule, making up the primary urine, and reabsorption occurs in the renal tubules - the absorption of most of the water, glucose, amino acids and some salts, resulting in the formation of final urine.

In each kidney there are up to a million nephrons, the totality of which makes up the main mass of the renal substance. To understand the structure of the kidney and its nephron, one must keep in mind its circulatory system. The renal artery originates from the aorta and has a very significant caliber, which corresponds to the urinary function of the organ associated with the "filtration" of blood.

At the hilum of the kidney, the renal artery divides according to the departments of the kidney into arteries for the upper pole, aa. polares superiores, for the bottom, aa. polares inferiores, and for the central part of the kidneys, aa. centrales. In the parenchyma of the kidney, these arteries go between the pyramids, that is, between the lobes of the kidney, and therefore are called aa. interlobares renis. At the base of the pyramids on the border of the medulla and cortex, they form arcs, aa. arcuatae, from which they extend into the thickness of the cortical substance aa. interlobulares.

From each a. interlobularis the bringing vessel departs vas afferens, which breaks down into tangle of tortuous capillaries, glomerulus, covered by the beginning of the renal tubule, the capsule of the glomerulus. The efferent artery that emerges from the glomerulus vas effects, secondarily breaks up into capillaries, which braid the renal tubules and only then pass into the veins. The latter accompany the arteries of the same name and leave the gate of the kidney with a single trunk, v. renalis falling into v. cava inferior.

Venous blood from the cortex flows first into stellate veins, venulae stellatae, then in vv. interlobulares accompanying the arteries of the same name, and in vv. arcuatae. The venulae rectae emerge from the medulla. from major tributaries v. renalis the trunk of the renal vein develops. In the region of sinus renalis veins are located in front of the arteries.

Thus, the kidney contains two systems of capillaries; one connects the arteries with the veins, the other is of a special nature, in the form of a vascular glomerulus, in which the blood is separated from the capsule cavity by only two layers of flat cells: the capillary endothelium and the capsule epithelium. This creates favorable conditions for the release of water and metabolic products from the blood.

Kidney anatomy instructional video

Understanding the structure and function of the kidney is impossible without knowing the characteristics of its blood supply. The renal artery is a large caliber vessel, it is a branch of the abdominal aorta. During the day, about 1500-1700 liters of blood passes through the human kidneys. Having entered the gate of the kidney, the artery divides into two branches, which successively branch into smaller and smaller vessels. Numerous interlobular arteries depart into the cortex, directed perpendicular to the cortex of the kidney. A large number of arteriole-bearing glomeruli depart from each interlobular artery; the latter break up into glomerular blood capillaries ("wonderful network" - the vascular glomerulus of the renal corpuscle), coil and pass into the arterial efferent vessels, which are divided into capillaries feeding tubules. From the secondary capillary network, blood flows into venules, continuing into the interlobular veins, then flowing into the arcuate and further into the interlobar veins. The latter, merging, form the renal vein. The medulla is nourished by blood, which, for the most part, has not passed through the glomeruli, which means that it has not been cleared of toxins.

There are two systems of capillaries in the kidneys: one of them (typical) lies on the path between arteries and veins, the other -