GFR of a diabetic person is 90 ml/min. Blood glucose is 200 mg/dl. Calculate urinary glucose excretion
rate if the Tm for glucose is 150 mg/min
Answer
Amount filtered of glucose = Plasma concentration * GFR
Here, its 90 ml/min * 200 mg/dl = 180 mg/min
Excretion rate of glucose = Amount filtered – Tubular maximum
Here, its 180 mg/min – 150 mg/min = 30 mg/min
So, the urinary glucose excretion rate = 30 mg/min
Handling of glucose by PCT
PCT resorbs 100% of filtered glucose. Other than PCT, no other nephron segment is capable of
glucose resorption
Once it fails to get resorbed in PCT…that’s it…glucose will eventually appear in urine
Glucose is resorbed along with sodium in PCT with the help of the transporter termed as Sodium
glucose cotransporter (SGLT)
Glucose moves out of the PCT cell through its basolateral side using GLUT-2 and enters
peritubular capillaries
Transport maximum of glucose (TmG)
Refers to the point where glucose carrier proteins in PCT are fully saturated
TmG is 375 mg/minute
Renal threshold for glucose
the plasma level at which the glucose first appears in the urine in more than the
normal minute amounts
Ideally it should be 300 mg/dL
But the observed renal threshold for glucose is 180 mg/dL