The GFR is affected by changes in pressure in the glomerular capillaries. If the pressure rises, the amount of fluid pushed into Bowman's capsule increases; and if the pressure drops, the amount of fluid being filtered decreases. Alterations to the diameter of the efferent and afferent arterioles control the pressure in the glomerular capillaries when arterial pressure changes—a process called autoregulation.

Click the buttons to change the diameters
of the Afferent and Efferent arterioles.

Afferent:	Dilate
	Normal
	Constrict
Efferent:	Dilate
	Normal
	Constrict

QUESTION: If blood pressure increases in the glomerulus, how does the diameter of the efferent and afferent arterioles need to change to bring the GFR back to normal?

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ANSWER: The afferent arteriole should constrict so less blood can enter the glomerulus, and the efferent arteriole should dilate so blood can leave more easily.