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Glomerular filtration rate (GFR) is the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time. [4] Central to the physiologic maintenance of GFR is the differential basal tone of the afferent (input) and efferent (output) arterioles (see diagram).
Both GFR and C Cr may be accurately calculated by comparative measurements of substances in the blood and urine, or estimated by formulas using just a blood test result (eGFR and eC Cr) The results of these tests are used to assess the excretory function of the kidneys.
In renal physiology, the filtration fraction is the ratio of the glomerular filtration rate (GFR) over the renal plasma flow (RPF). Filtration Fraction, FF = GFR/RPF, or =. The filtration fraction, therefore, represents the proportion of the fluid reaching the kidneys that passes into the renal tubules. It is normally about 20%.
This is the numerator in the equation. The denominator is the total amount of sodium filtered by the kidneys. This is calculated by multiplying the plasma sodium concentration by the glomerular filtration rate (GFR) calculated using creatinine filtration. The flow rates then cancel out, simplifying to the standard equation: [1]
Para-aminohippurate (PAH) clearance is a method used in renal physiology to measure renal plasma flow, which is a measure of renal function. [citation needed]PAH is completely removed from blood that passes through the kidneys (PAH undergoes both glomerular filtration and tubular secretion), and therefore the rate at which the kidneys can clear PAH from the blood reflects total renal plasma flow.
Many laboratories will automatically calculate eGFR when a creatinine test is requested. Algorithms to estimate GFR from creatinine concentration and other parameters are discussed in the renal function article. Unfortunately, the MDRD Study equation was developed in people with chronic kidney disease, and its major limitations are imprecision ...
Typically, in an adult human, the net filtration pressure is 10mmHg and Kf 12.5mL/min/mmHg, giving a glomerular filtration rate (GFR) of 125mL/min. A decrease in Kf due to reduced number of glomeruli or reduced permeability will reduce the GFR at a given filtration pressure [3]
Renal corpuscle showing glomerulus and glomerular capillaries Figure 2: (a) Diagram of the juxtaglomerular apparatus: it has specialized cells working as a unit which monitor the sodiujuxtaglomerular apparatus: it has three types of specm content of the fluid in the distal convoluted tubule (not labelled - it is the tubule on the left) and adjust the glomerular filtration rate and the rate of ...