The body is an amazing collection of organs and tissues that work harmoniously to maintain human life. And the main process that supports life is metabolism. As a result of the breakdown of substances, the energy necessary for the flow of basic biological processes is synthesized. However, along with energy, potentially harmful metabolic products are also formed. They must be removed from the cell, intercellular fluid and blood by the kidneys. In the kidneys, filtration occurs in the glomerular apparatus, a special structure of the active nephron into which the bringing arteriole flows.
The structural feature of the nephron
Nephron - a collection of cells that form a capsule and glomerulus with channels extending from it, designed to filter blood plasma and drain urine. This is the elementary functional unit of the kidney, responsible for urination. Nephron consists of a glomerulus, which has its own capsule. The arteriole, a blood vessel, flows into it, through which blood enters the glomerulus. Many small arterioles depart from the arteriole, which form the glomerulus and assemble into a larger - arteriole.
The latter in diameter is much smaller than the supply, which is necessary to maintain high pressure (about 120 mmHg) at the inlet. Due to this, the hydrostatic pressure in the glomerulus increases, and therefore almost all the liquid is filtered, and not carried out into the discharge arteriole. Only due to hydrostatic pressure, approximately equal to 120 mm Hg, there is such a process as renal filtration. Moreover, in the kidneys, blood filtration occurs in the glomerulus of the nephron, and its speed is almost 120 ml per minute.
Renal Filtration Characterization
Glomerular filtration rate is one of the indicators by which the functional state of the kidneys is determined. The second indicator is reabsorption, which normally makes up almost 99%. This means that almost all of the primary urine that got from the nephron glomerulus into the convoluted tubule after passing through the descending tubule, loop of Henle and the ascending tubule is absorbed back into the blood along with nutrients.
Blood flow to the kidneys is carried out through the arteries, which normally consume a quarter of the total minute volume of blood circulation, and the filtered one is discharged through the veins. This means that if the systolic ejection of the left ventricle of the heart is 80 ml, then 20 ml of blood will be captured by the kidneys, and another 20 ml by the brain. The remaining 50% of the total systolic volume provides the needs of other organs and tissues of the body.
The kidneys are organs that take a huge part of the blood circulation, but they need blood not only for metabolism, but for filtering. This is a very fast and active process, the speed of which is easy to track by the example of intravenous dyes and radiopaque substances. After their intravenous administration in the kidneys, blood filtration occurs in the glomerular apparatus of the cortical substance. And already in 5-7 minutes after getting it can be seen in the renal pelvis.
Kidney Filtration
In fact, the contrast goes from the venous to the lung, then to the heart and then the renal artery in 20-30 seconds. In another minute, he enters the renal glomerulus, and after a minute, through the collecting ducts located in the pyramids of the kidneys, it collects in the renal cups and is secreted into the pelvis. All this takes about 2.5 minutes, but only at 5-7 minutes the concentration of contrast in the pelvis rises to values that allow you to notice the excretion on x-rays.
That is, the filtration of drugs, poisons or metabolic products is actively taking place after 2.5 minutes in the blood. This is a very fast process, which is possible due to the special structure of the nephron. In the kidneys, blood filtration occurs in these structures, the glomeruli of which are located in the cortical substance. In the medulla of the kidneys are located only the tubules of the nephron. Therefore, it is right to say that filtration occurs in the cortical layer of organs.
Many are mistaken when they claim that in the kidneys, blood filtration occurs in the pyramids. This is a mistake, since they mainly contain only collective nephron tubes, convoluted, descending and ascending tubules, as well as the Henle loop. This means that in the pyramids, the main process is reabsorption and concentration of urine, after which it is collected and secreted into the renal pelvis. The filtration itself takes place in the cortical layer of the kidney, which is richly supplied with blood.
Special functions of the renal tubules
In the kidneys, blood filtration occurs in capsules of nephrons, more precisely, in the glomerular apparatus. Here, primary urine is formed, which is a blood plasma without major high molecular weight proteins. The epithelium, which lines the renal tubules from the inside, has special functions. Firstly, it is able to absorb water and electrolytes, returning it to the vascular bed.
Secondly, epithelial cells can absorb low molecular weight proteins, which will also be transferred to the blood without destroying their structure. Thirdly, the nephron tubule epithelium is capable of independently synthesizing amino acids by transamination and glucose by gluconeogenesis from amino acid residues. But this process is not chaotic, but regulated by the body.
This means that epithelial cells have a number of receptors that receive a signal from mediator molecules, activating either the synthesis of amino acids or glucose. The fourth feature of the renal glomerular epithelial lining is its ability to absorb monosaccharides in the form of glucose-6-phosphate.
Summary
The kidneys are organs of the urinary system in which filtration occurs. Thanks to it, nephrons remove water-soluble compounds from the blood, maintaining the acid-base balance of the body. A common misconception is that in the kidneys, blood filtration occurs in the convoluted tubules. In fact, the already filtered liquid - primary urine - enters the convoluted tubule from the glomerulus capsule. In the convoluted glomerulus, the main task of the epithelium is the absorption of water and the implementation of the concentration function.