3. Physiology
        3.12. Renal
3.12.3. Glomerular filtration rate

Glomerular filtration rate

[Ref: AV6:Chp2]

Normal values


Filtration process

Filtrates go through

  1. Fenestrae in the glomerular capillary endothelial layer
  2. Basement membrane
  3. Slit diaphragms between podocyte foot processes


Properties that influence filtration

Filtration depends on

Molecular size

MW < 7000d
--> Passes freely

[WG21:p710] <3.6-4nm --> Also pass freely if neutral or cation

Electric charge

Barrier is negative charged



Starling forces

GFR = k x (HPc-HPb-OPc)


Filtration coefficient

Contraction of glomerular mesangial cells
--> Reduction in area available for filtration
--> Increase filtration coefficient
--> Decrease GFR

Hydrostatic pressure in glomerular capillaries

Vasoconstriction of the afferent arteriole
--> Reduction in HPc
--> Decrease GFR

Vasoconstriction of the efferent arteriole
--> Increase in HPc
--> Increase GFR


GFR can be regulated independently of RBF.

Hydrostatic pressure in Bowman's capsule

Significant only in cases like urinary tract obstruction.

Oncotic pressure in glomerular capillaries

Oncotic pressure of plasma increases progressively as it moves from the afferent arteriole to the efferent arteriole side


Autoregulation of GFR

GFR is strongly influenced by renal arterial pressure

Increase in BP
--> Increased salt and water excretion
--> i.e. Pressure natriuresis and diuresis


Autoregulation of GFR

Myogenic autoregulation blunts changes in GFR due to changes in blood pressure
--> But the small changes in BP and GFR still cause large changes in urine output

Autoregulation of RBF


Regulation of RBF


Renal sympathetic nerve activity
* Strong sympathetic stimulation causes a marked decrease in RBF (mediated by alpha1-receptors)

Angiotensin II
* Efferent more than afferent

RBF is decreased during exercise and on standing

Regulation of GFR

GFR is mostly controlled by changing the resistance of the afferent arterioles and efferent arterioles

GFR is decreased by

Other factors that influence GFR


Other notes


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