Yuxtaglomerular apparatus of the kidney: structure and function
The elementary functional unit of the kidneys is nephron, a structure that is directly responsible for the filtration of blood plasma. The most important component of its functioning is the maintenance of arterial pressure in constant values. For this physiological indicator is the Yuxtaglomerular apparatus( SOA), directly related to the nephron. It is the most important regulator of blood pressure in the body, which maintains adequate blood supply to the kidneys.
Features of the structure of the kidneys
Kidneys are hormone-active parenchymatous paired organs of urination. A person has a lumbar location 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 the systolic ejection. Under the influence of blood pressure, blood is pushed to small afferent arterioles, where it enters the capsule of the glomerulus and is filtered.
Formal blood elements and some part of its plasma are diverted from the efferent arteriole, which is much less afferent in diameter. This is necessary to maintain a higher inlet fluid pressure, which supports filtration, providing only a small discharge to the discharging arteriol. Also, the regulator of pressure 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 South
The Yuxtaglomerular apparatus consists of three types of cells located in the immediate vicinity of the nephron and forming with it a functional system with positive feedback. The first type of cells is epithelioid( or granular), which is a modified smooth muscle wall myocytes of the arteriola. They are located in a large number in the muscular layer of the afferent arteriol and in the smaller - in the efferent. This indicates their involvement in the determination of the difference in hydrostatic pressure in these vessels.
In granular cells there are baroreceptors that transmit information to the juxtavascular cells of the SOUTH.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 the link between the epithelial cells and the dense spot of the urinary tubule. The juxtavascular cells are located in the space between the afferent and outgoing arterioles of the SOUTH.
Dense spot of the South
The third type of cells of the juxtaglomerular apparatus are cells of a dense spot located in the distal parts of the urinary tubule of the nephron. These components of the SOA are carried by osmoreceptors, through which they are able to determine the sodium concentration. They track the changes in the content of sodium ions in the already filtered urine, from which nutrients and liquid were 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. These granular cells, on the basis of the information obtained, release a certain amount of the enzyme renin in order to influence the blood pressure index. Thus, SOA is the structure that directly participates in the urine filtration rate. Together with the nephron they form an integral functional system supporting 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. Epitheliocytes of the SOA are modified smooth muscle cells having a flattened shape. Their nucleus is polygonal, and organelles are presented in small amounts. Their task is to synthesize the enzyme renin, and therefore the biosynthetic apparatus in epithelial cells, also called granular cells, is highly developed. In this case, the grains in the cytoplasm are plasma tanks with formed renin.
Features of the regulation of blood pressure
The Yuxtaglomerular apparatus is an example of a hormonal-active structure that has input data in the form of arterial pressure and the ability to influence it through the synthesis of renin. And the effectiveness of monitoring blood pressure directly depends on the amount of fluid in the body and the state of arterial vessels. In conditions of ischemia, when atherosclerotic narrowing of arteries is observed in the main target organs of the human body, the SOUTH provides an increase in pressure values in order to maintain a sufficient rate of filtration in the glomeruli.
This function does not depend on how many kidneys a person has, since it is regulated by the strongest enzyme systems. But in the case of hypertension, the filtration efficiency due to higher pressure( above 120 mmHg ) does not increase in proportion to the growth of blood pressure. It is most effective at a pressure of 120-140 mmHg. And in the case of an increase in the index of blood pressure, there is a risk of damage to the glomeruli, because of which the uxtaglomerular apparatus stops or reduces the synthesis of renin.
Effect of AD on the functions of SOHA and kidneys
Prolonged increase in blood pressure leads to a shift in the balance and unbalance of the angiotensin system and SOUTH.This means that against a 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 fibrosis of the arteries, the efficiency of the angiotensin mechanism is small: it leads to an increase in pressure, but it does not grow in the arterial artery. This explains how the location of the kidneys and the SOUTH affect the whole blood circulation and its regulation . In addition to this, hypertension leads to nephrosis to lerosis - the gradual death of kidney nephrons, which is why AH is often a prerequisite for renal failure. Then, no matter how many kidneys a person has, there is a marked decrease in the rate of filtration and the effectiveness of renal functions.