Foot Fetish

2+ Year Member
Jun 4, 2016
Medical Student
The figure on page 281 of Costanzo says that dilation of the afferent arteriole (mediated by decreased sympathetic activity in response to increased salt intake) results in increased GFR, which in turn causes decreased reabsorption of Na+ in the proximal tubule.

Doesn't this go against the principle of glomerulotubular balance, which states that increases in filtration at the glomerulus are balanced by increases in reabsorption at the PCT?

ASM student

2+ Year Member
May 1, 2016
Increased GFR will decrease RAS activity decreasing Na reabsorption. This is a way of Na homeostasis in which increased Na will cause extracellular volume expansion increasing GFR (increased NaCl delivery to Macula dansa) while decreasing RAS activity allowing loss of excess Na.

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