The elementary functional unit of the kidneys is the nephron, a structure that is directly responsible for filtering blood plasma. The most important component of its functioning is the maintenance of arterial pressure at constant values. The juxtaglomerular apparatus (JGA), which is directly connected with the nephron, is responsible for this physiological indicator. It is the most important regulator of blood pressure in the body, maintaining an adequate blood supply to the kidneys.
Features of the structure of the kidneys
Kidneys are hormonally active parenchymal paired urinary organs. In humans, there is a lumbar location of the kidneys, in which the organs are connected to the aorta by short renal arteries. They provide an abundant blood supply, which is 25% of systolic output. Under the influence of blood pressurepushes to small afferent arterioles, where it enters the glomerular 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 one in diameter. This is necessary to maintain a higher inlet fluid pressure, which maintains filtration by providing only a small discharge to the efferent arteriole. Also, the pressure regulator is the juxtaglomerular apparatus of the kidneys. It is a collection of cells directly related to the synthesis of renin and its regulation.
Morphology of the YUGA
The juxtaglomerular apparatus consists of three types of cells located in close proximity to the nephron and forming a functional system with positive feedback with it. The first type of cells is epithelioid (or granular), which are modified smooth myocytes of the muscular wall of the arteriole. They are located in large numbers in the muscular layer of the afferent arteriole and in smaller numbers in the efferent. This indicates their involvement in determining the difference in hydrostatic pressure in these vessels.
The granular cells have baroreceptors that transmit information to the juxtavascular cells of the JGA. Granular cells are also the main producers of renin, an enzyme that regulates blood pressure in the circulatory system. This enzyme is also partially capable of synthesizing juxtavascular cells (the second type) of the juxtaglomerular apparatus. The functions of these cells are reduced to the fact that they are a link between epitheliocytes and a dense spot of the urinary tubule. Juxtavascular cells are located in the space between the afferent and efferent arterioles of the JUGA.
Dense Stain SOUTH
The third type of cells of the juxtaglomerular apparatus - cells of the dense spot located in the distal parts of the urinary tubule of the nephron. These JGA components carry osmoreceptors, through which they are able to determine the sodium concentration. They track changes in the sodium ion content of already filtered urine from which nutrients and fluid have been reabsorbed. Depending on the concentration values, the macula densa cells transmit information to the juxtavascular cells.
The latter process the signal and regulate the function of epitheliocytes. These granular cells, based on the information received, secrete a certain amount of the enzyme renin to influence the blood pressure. Thus, the JGA is the structure that is directly involved in the site in the rate of urine filtration. Together with the nephron, they form an integral functional system that supports the vital activity of the human body.
Structure of juxtaglomerular cells
The cells of the juxtaglomerular apparatus located in the kidneys have a special structure. JGA epitheliocytes are modified smooth muscle cells with a flattened shape. Their nucleus is polygonal, and organelles are represented in small numbers. Themthe task is to synthesize the enzyme renin, and therefore the apparatus of biosynthesis in epitheliocytes, which are also called granular cells, is highly developed. At the same time, grains in the cytoplasm are plasmatic tanks with formed renin.
Features of blood pressure regulation
The juxtaglomerular apparatus is an example of a hormonally active structure that has blood pressure input and the ability to influence it through renin synthesis. 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, JGA provides an increase in pressure values in order to maintain a sufficient glomerular filtration rate.
This function does not depend on how many kidneys a person has, as it is regulated by the strongest 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 pressures of 120-140 mmHg. And in the case of an increase in blood pressure, there is a risk of damage to the glomeruli, due to which the juxtaglomerular apparatus stops or reduces the synthesis of renin.
Effect of blood pressure on the functions of JUGA and kidneys
Prolonged increase in blood pressure leads to a shift in the balance and imbalance of the angiotensin system and JGA. This means that onagainst the background of narrowing of the renal arteries due to atherosclerosis and against the background of the subsequent development of hypertension, there is an increase in renin production. However, due to arterial fibrosis, the efficiency of the angiotensin mechanism is low: it leads to an increase in pressure, but it does not increase in the afferent arteriole. This explains how the location of the kidneys and the JGA affects the entire circulation and its regulation. In addition, hypertension leads to nephrosclerosis - the gradual death of kidney nephrons, which is why hypertension is often a prerequisite for renal failure. Then, no matter how many kidneys a person has, there is a noticeable decrease in the filtration rate and efficiency of kidney functions.
