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584 SeCTIOn III Renal ` RENAL—PhysioLogy Renal ` RENAL—PhysioLogy
Calculation of Filtered load = GFR × P .
x
reabsorption and Excretion rate = V × U .
x
secretion rate Reabsorption rate = filtered – excreted.
Secretion rate = excreted – filtered.
Fe = fractional excretion of sodium.
Na
Na excreted V × U P × U U × V
+
Na
Fe Na = Na ltered = GFR × P Na = U Cr × P Na where GFR = Cr P Cr
+
Cr
Na
Glucose clearance Glucose at a normal plasma level (range 60–120 Glucosuria is an important clinical clue to
mg/dL) is completely reabsorbed in proximal diabetes mellitus.
convoluted tubule (PCT) by Na /glucose Splay phenomenon—T for glucose is reached
+
m
cotransport. gradually rather than sharply due to the
In adults, at plasma glucose of ∼ 200 mg/dL, heterogeneity of nephrons (ie, different T
m
glucosuria begins (threshold). At rate of points); represented by the portion of the
∼ 375 mg/min, all transporters are fully titration curve between threshold and T .
m
saturated (T ).
m
Normal pregnancy is associated with GFR. 600 Filtered
With filtration of all substances, including Excreted
glucose, the glucose threshold occurs at lower 450 T ~ 375mg/min Reabsorbed
m
plasma glucose concentrations glucosuria at
normal plasma glucose levels. Glucose transport (mg/min) 300
Sodium-glucose cotransporter 2 (SGLT2) 150 “Splay”
Renal
inhibitors (eg, -flozin drugs) result in threshold
glucosuria at plasma concentrations 0
< 200 mg/dL. 0 200 400 600 800
Normal Plasma glucose (mg/dl)
FAS1_2019_14-Renal.indd 584 11/7/19 5:42 PM
