The renal corpuscle is the name given to the structural unit of the kidney. This histologic unit consists of a capillary vascular tangle and a so-called Bowman’s capsule that surrounds the renal corpuscle.
What is a renal corpuscle?
Together with the renal tubule, the renal tubule, the renal corpuscle forms one of the smallest functional units of the nephron, the kidney. Each kidney has approximately 1.4 to 1.5 million such renal corpuscles, which are distinguished with a vascular pole and a urinary pole. The renal corpuscles act like filters, as a quarter of the blood always passes through the kidneys. When the urine passes into the renal pelvis, it is already called secondary urine and is only one percent of the primary urine volume. Controlled is the reabsorption of fluid by the hormone ADH, adiuretin.
Anatomy and structure
The renal corpuscle, also called the corpusculum renale, is a part of the so-called nephron and forms primary urine as an ultrafiltrate of blood. The renal corpuscles are approximately 0.2 millimeters in size and have a spherical shape. They are located within the cortex of the kidney. The components of the renal corpuscle are a capillary vascular tangle encased in a double-walled capsule called the Bowman capsule. This Bowman capsule, when inverted, carries a fine capillary tangle called the glomerulus. Together, these structures form a blood-urine barrier. Blood components are forced out of this glomerulus into a system of tubes that eventually excrete urine. The tube system begins at Bowman’s capsule and ends at the nephron, the kidney. There, the urine enters the renal pelvis, then the ureters and bladder. The cortical labyrinth forms a length of several kilometers in the two kidneys. The downright tiny blood vessels in the renal corpuscles have pores that are permeable to water. Thus, it is possible through the pores to filter out the toxins in the body that have been produced in metabolism. The pores let through toxins, but not the important proteins, vitamins or larger blood cells. The limit for this pore permeability is a corresponding molecular weight of 5 to 10,000.
Function and tasks
Among the most important tasks of the renal corpuscle is the ultrafiltration of blood into what is called primary urine. Approximately one liter of blood passes through the kidneys every minute. Twenty percent of this is filtered in a minute. This amount of fluid of about 125 millimeters per minute, 180 liters per day, is decisive for diagnostics. It reflects the functional capacity of the kidneys. Crucial for the filtration process is the blood pressure in the glomerular vessels, which is subject to daily fluctuations such as sleep, stress or physical confirmation. The kidney is able to adjust the blood pressure to the current requirements. This process is called autoregulation of the kidney and occurs with the help of the pressure receptors in the blood vessels supplying and discharging the renal corpuscle. If the blood pressure is too high, the supplying arteries dilate; if the blood pressure is too low, the outgoing vessels of the glomerulus constrict. Since the kidney is a detoxification organ, but also regulates the salt, water and hormone balance, the functions of the renal corpuscles are very important. After filtration, the urine is further processed. The kidney supports the formation of red blood cells and bone metabolism. It protects the human organism from possible overhydration, but also from dehydration and regulated salt content of the body. Through the hormones as well as the influences of our autonomic nervous system, the amount of water that is recovered is regulated, but also the function of the kidneys is adjusted. In the case of tubular secretion, substances foreign to the body, such as medications, uric acid, ammonia, as well as urea and other substances, are excreted more quickly. In particular, the excretion of drugs occurs with the help of active transporters called carriers. Degradation products continue to circulate in the blood. This can increase the effect of drugs or lead to an interaction between several drugs. If there is a constant excess of uric acid in the blood, deposition in the joints is possible, which can lead to gout.
Diseases
In certain diseases, such as hypertension or diabetes mellitus, blood pressure is elevated, but a blood pressure that is constant is important for filtration, which occurs in the glomeruli.The autoregulation of the kidney ensures that the blood pressure remains as constant as possible without affecting the filtration processes of the kidney. The pressure sensors react extremely sensitively and intervene in a regulating manner in the event of fluctuations. If protein is detected in the urine, this may be a sign of possible kidney disease. The concentration of urine and the subsequent recovery of salts and water requires a lot of energy. In the case of possible renal insufficiency, the important concentration of urine no longer functions completely, which requires increased urine production and often repeated emptying of the bladder, sometimes at night. If the level of the hormone ADH, adiuretin, is too low, diabetes insipidus can result, causing the excretion of up to 20 liters of fluid daily. Only a certain amount of amino acids and glucose can be reabsorbed. In the case of insulin deficiency, too much glucose circulates in the blood, which is then excreted in the urine. Glomerulonephritis is an inflammation of the renal corpuscles in which the kidney tissue is inflamed. The cause is probably that constant contact from the vascular tangles in the renal corpuscle with pollutants in the blood causes an inflammatory response, or hereditary factors are equally responsible.
