H1v: Renal handling of glucose

  • Glucose = dietary monosaccharide used for aerobic metabolism
  • Glycosuria = excretion of glucose in urine → pathological

Renal Handling

Filtration: glucose is freely filtered

  • Filtered glucose = GFR x [plasma glucose]

= 125mL/min x 80mg/dL

= 12.5dL/min x 80mg/dL

= 100mg/min

Reabsorption: all glucose is completely reabsorbed by active transport

  • Na/K/ATPase creates electrochem gradient on BL membrane (active transport)
  • SGLUT carries glucose coupled to Na= on apical membrane (2nd active transport)
  • Enters renal ISF via GLUT transporter (facilitated diffusion) → peritubular caps

→ Concentration of glucose in tubules falls rapidly, faster than H2O

→ ∴indicates it is actively reabsorbed

  • Reabsorption occurs at PCT
  • Secretion does not occur
  • It should NOT appear in the urine

Transport Maximum

All organic solutes have a TMAX

  • Plasma glucose 5 – 10mmol/L
  • TMAX glucose = 16mmol/L x 0.125L/min

         = plasma [glucose] x GFR

                                         = 2mmol/min

  • ∴ If plasma glucose > TMAX glucose → glycosuria
Transport Maximum

TMAX = 16mmol/L → which for this graph is 300mg/dL

Consequences of Glycosuria

  • Loss of energy substrate
  • Loss of fluid → any glucose not reabsorbed is an osmole in the tubule which prevents H2O reabsorption
  • Loss of K+ → K+ secretion ∝flow ∴↑flow = ↑K+ loss
  • Predisposes to UTI