Glomerular Filtration Rate
Dr.V.Kasiviswanathan
Erode
Definition
Glomerular filtration rate (GFR) is the rate of fluid filtered through the glomerulus into the Bowman's capsule of the kidney per minute per 1.73 m²
Normal results range from 90 to 120 mL/min/1.73 m2. Older people will have lower than normal GFR levels, because GFR decreases with age.
Factors regulating GFR
Changes in renal blood flow
Changes in systemic blood pressure
Changes in glomerular capillary hydrostatic pressure
Afferent or efferent arteriolar constriction
Changes in hydrostatic pressure in Bowman's capsule
Ureteral obstruction
Edema of kidney inside tight renal capsule
Changes in concentration of plasma : dehydration, hypoproteinemia etc
Changes in K
Changes in glomerular capillary permeability
Changes in effective filtration surface area
Molecular weight
< 7000 Daltons - molecules will be freely filtered
> 70000 Daltons - molecules are essentially not filtered at all
In between 7000 and 70000 Daltons - the percentage of a given molecule that is filtered decreases with increasing weight
The surface area of the filter
The thickness or permeability of the filter
Magnitude of any forces favouring filtration
Magnitude of any forces opposing filtration
GFR increases with:
Increased glomerular blood flow
Decreased afferent arteriolar resistance
Increased efferent arteriolar resistance
Sympathetic stimulation (extreme situations only) lowers GFR - Norepinephrin and Epinephrin lower GFR
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Define glomerular filtration rate and mention its normal value. Explain the factors regulating glomerular filtration rate. (1+1+8=10)
