Glomerular filtration rate (GFR) describes the flow rate of filtered fluid through the kidneys. It represents the total amount of filtrate formed by all the renal corpuscles in both kidneys per minute. The glomerular filtration rate is directly proportional to the net filtration pressure, so a fluctuation in pressure will change the GFR. Prolonged changes in normal GFR will cause either too much or too little water and solutes to be removed from the blood. Conditions that can affect GFR include: arterial pressure, afferent arteriole constriction, efferent arteriole constriction, plasma protein concentration, and colloid osmotic pressure. The glomerular blood pressure provides the driving force for fluid and solutes to be filtered out of the blood and into the space made by Bowman's capsule. The remainder of the blood not filtered into the glomerulus passes into the narrower efferent arteriole.
Glomerular filtration rate (GFR) is the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time. Central to the physiologic maintenance of GFR is the differential basal tone of the afferent and efferent arterioles. GFR is equal to the Clearance Rate when any solute is freely filtered and is neither reabsorbed nor secreted by the kidneys.
Therefore, the rate measured is the quantity of the substance in the urine that originated from a calculable volume of blood. Relating this principle to the below equation - for the substance used, the product of urine concentration and urine flow equals the mass of substance excreted during the time that urine has been collected. This mass equals the mass filtered at the glomerulus as nothing is added or removed in the nephron. Dividing this mass by the plasma concentration gives the volume of plasma which the mass must have originally come from, and thus the volume of plasma fluid that has entered Bowman's capsule within the aforementioned period of time Figure 1. The GFR is typically recorded in units of volume per time, e.g., milliliters per minute (ml/min).
In the physiology of the kidneys, tubuloglomerular feedback (TGF) is one of several mechanisms the kidneys use to regulate glomerular filtration rate (GFR). Changes in GFR are detected by the renal tubule, which sends feedback signals to the glomerulus, initiating a cascade of events that ultimately brings GFR to an appropriate level. The macula densa serves as the detector, while the glomerulus acts as the effector.