The primary urine (or fore urine ) is a largely protein-free ultrafiltrate, which is formed by the kidney corpuscles when the kidneys are supplied with blood and which can essentially be described as urine that is not yet concentrated . The primary urine is also called tubular fluid .
By definition, primary urine formation is identical to the glomerular filtration rate and creatinine clearance . In this respect, the primary urine flow is a measure of the kidney's filtration function. Too little primary urine flow is known as kidney failure or kidney filter failure . Severe bilateral renal insufficiency is known as acute kidney failure or chronic kidney failure . Renal failure can have two different causes. On the one hand, kidney disease (or lower urinary tract disease ) can lead to renal failure; second, any reduction in cardiac output leads to renal insufficiency.
This process was first described in 1842 by Carl Ludwig (1816–1895) in his habilitation thesis De viribus physicis secretionem urinae adjuvantibus ("Contributions to the doctrine of the mechanism of urinary secretion").
A person's total amount of blood flows through their two kidneys about 300 times a day , a total of about 1500 liters for adults. As renal blood flow , the amount of blood is referred to, which flows per minute through the kidneys as renal plasma flow , the amount of the kidneys per minute flowing through the blood plasma . The renal plasma flow is the product of renal blood flow , and (1 - hematocrit ). From the renal plasma flow over a fifth is about in the podocytes filter the glomeruli. The filtration fraction is calculated by dividing the glomerular filtration rate (GFR) by the renal plasma flow.
As a result, the GFR of each individual kidney is about one percent of cardiac output (CO); only in parenchymal kidney diseases does this percentage decrease. But even with nephropathy , GFR and CO are roughly proportional . A proportionality factor GFR / HZV <0.02 thus proves to a certain extent the presence of an actual kidney disease. Conversely, a quotient GFR / CO ≈ 0.02 indicates kidney health in the case of renal insufficiency; the patient has extrarenal kidney syndrome .
Around 180 liters of primary urine are produced every day. This corresponds to a GFR = 125 ml / min. With the exception of the macromolecules , which are partially retained from a molecular mass of 6-15 kilodaltons (kDa) and from a molecular mass of approx. 80 kDa, the composition of the primary urine corresponds to that of the blood plasma.
On the way through the kidney tubules , the secondary urine ( urine , urine, terminal urine ) is formed from the primary urine through absorption and secretion processes . Only about one percent of the primary urine, i.e. about one and a half liters per day in adults, reaches the urinary bladder as secondary urine and is excreted as urine . The tubular resorption rate is therefore normally around 99%; in anuria it reaches almost 100%. Diuretics reduce reabsorption and increase the volume of secondary urine.
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