The elementary functional unit of the kidneys is the nephron, a structure that is directly responsible for the filtration of blood plasma. The most important component of its functioning is the maintenance of blood pressure at constant values. The juxtaglomerular apparatus (JGA), directly associated with the nephron, is responsible for this physiological indicator. It is the most important regulator of blood pressure in the body, supporting an adequate blood supply to the kidneys.
Features of the structure of the kidneys
The kidneys are hormone-active parenchymal paired urinary organs. A person has a lumbar arrangement of the kidneys, in which the organs are connected to the aorta by short renal arteries. They provide abundant blood supply, which is 25% of systolic discharge. Under the influence of blood pressure, the blood is pushed to small afferent arterioles, where the glomerulus enters the capsule and is filtered.
The formed elements of the blood and some of its plasma are discharged along the efferent arteriole, which is much smaller than the afferent in diameter. This is necessary to maintain a higher inlet fluid pressure, which supports filtration, providing only a small discharge into the outlet arteriole. The juxtaglomerular apparatus of the kidneys is also a pressure regulator. It is a collection of cells directly related to the synthesis of renin and its regulation.
Morphology South
The juxtaglomerular apparatus consists of three types of cells located in close proximity to the nephron and forming with it a functional system with positive feedback. The first type of cells is epithelioid (or granular), which are modified smooth myocytes of the muscle wall of the arteriole. They are in large numbers located in the muscle layer of the afferent arteriole and in a smaller one - in the efferent. This indicates their involvement in determining the difference in hydrostatic pressure in these vessels.
In granular cells, there are baroreceptors that transmit information to the justavascular cells of the South Africa. Granular cells are also the main producers of renin, an enzyme that regulates blood pressure in the circulatory system. This enzyme is also partially able to synthesize juxtavascular cells (second type) of the juxtaglomerular apparatus. The functions of these cells are reduced to the fact that they are a connecting link between epithelial cells and a dense spot of the urinary tubule. Juxtavascular cells are located in the space between the afferent and efferent arterioles of the South Autonomous Area.
Dense spot South
The third type of cells of the juxtaglomerular apparatus is dense spot cells located in the distal parts of the urinary tubule of the nephron. These components of the SGA carry osmoreceptors, through which they are able to determine the sodium concentration. They monitor changes in sodium ion content in already filtered urine, from which nutrients and fluid are reabsorbed. Depending on the concentration values, dense spot cells transmit information to juxtavascular cells.
The latter process the signal and regulate the function of epithelial cells. Based on the information received, these granular cells secrete a certain amount of the renin enzyme in order to influence the blood pressure index. Thus, SGA is the structure that directly participates in the urine filtration rate on the spot. Together with the nephron, they form an integral functional system that supports the vital functions of the human body.
The structure of juxtaglomerular cells
Juxtaglomerular apparatus cells located in the kidneys have a special structure. Epithelial cells of the south ernal arteries are modified smooth muscle cells with a flattened shape. Their core is polygonal, and organelles are represented in small numbers. Their task is the synthesis of the renin enzyme, and therefore the biosynthesis apparatus in epithelial cells, which are also called granular cells, is highly developed. In this case, the grains in the cytoplasm are plasma tanks with formed renin.
Features of blood pressure regulation
The juxtaglomerular apparatus is an example of a hormonally active structure that has input in the form of blood pressure and the ability to influence it through the synthesis of renin. Moreover, the effectiveness of blood pressure control directly depends on the amount of fluid in the body and the state of arterial vessels. In conditions of ischemia, when atherosclerotic narrowing of the arteries is observed in the main target organs of the human body, SGA provides an increase in pressure values โโin order to maintain a sufficient filtration rate in the glomeruli.
This function does not depend on how many kidneys a person has, since it is regulated by the most powerful enzyme systems. But in the case of the development of arterial hypertension, the filtration efficiency due to higher pressure (above 120 mmHg ) does not increase in proportion to the increase in blood pressure. It is most effective at a pressure of 120-140 mmHg. And in the case of an increase in blood pressure, there is a risk of damage to the glomeruli, because of which the juxtaglomerular apparatus stops or reduces the synthesis of renin.
The effect of blood pressure on the function of the south and kidneys
A prolonged increase in blood pressure leads to a shift in equilibrium and an imbalance of the angiotensin system and SGA. This means that against the background of narrowing of the renal arteries due to atherosclerosis and against the background of the subsequent development of hypertension, an increase in renin production occurs. However, due to arterial fibrosis, the efficiency of the angiotensin mechanism is not high: it leads to an increase in pressure, but it does not increase in the leading arteriole. This explains how the location of the kidneys and SGA affects all blood circulation and its regulation . In addition, hypertension leads to nephros to lerosis, a gradual death of kidney nephrons, which is why hypertension is often a prerequisite for renal failure. Then, regardless of how many kidneys a person has, there is a noticeable decrease in the rate of filtration and the effectiveness of renal functions.