In renal physiology, the<unk>  is the ratio of the glomerular<unk>  rate (GFR) over the renal plasma flow (RPF).<unk> ,<unk>  = GFR/RPF, or . The<unk> , therefore, represents the proportion of the fluid reaching the kidneys that passes into the renal tubules. It is normally about 20%. GFR on its own is the most common and important measure of renal function. However, in conditions such as renal artery stenosis, blood flow to the kidneys is reduced.<unk>  must therefore be increased in order to perform the normal functions of the kidney. Loop diuretics and thiazide diuretics decrease<unk> . Catecholamines (norepinephrine and epinephrine) increase<unk>  by vasoconstriction of afferent and efferent arterioles, possibly through activation of alpha-1 adrenergic receptors. Severe hemorrhage will also result in an increased<unk> .
Filtration fraction
Diffusing capacity
PAH clearance
Gas exchange
Renal threshold
Effective circulating volume
Tidal volume
Free water clearance