What is the role of glucose homeostasis in renal glucosuria?

Updated: Dec 10, 2018
  • Author: Rajendra Bhimma, MBChB, MD, PhD, DCH (SA), FCP(Paeds)(SA), MMed(Natal); Chief Editor: Craig B Langman, MD  more...
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Answer

The kidneys play an important role in glucose homeostasis. It helps to maintain glucose homeostasis by at least two mechanisms. [6]

  • Under normal circumstances, the kidney filters and reabsorbs 100% of glucose, approximately 180 g (1 mole) of glucose, each day. The glucose transporters expressed in the renal proximal tubule ensure that less than 0.5 g/day (range 0.03-0.3 g/d) is excreted in the urine of healthy adults. More water than glucose is reabsorbed resulting in an increase in the glucose concentration in the urine along the tubule. Consequently the affinity of the transporters for glucose along the tubule increases to allow for complete reabsorption of glucose from the urine.

  • It produces glucose by gluconeogenesis. The key enzymes of gluconeogenesis are phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6-phosphatase (G6Pase). These are expressed in the renal proximal tubule only and not the renal medulla. The kidneys produce between 2.0-2.5umol of glucose/kg/min thereby contributing about 20-25% of circulating glucose. [7]

Gluconeogenesis in the kidneys exceeds renal glucose consumption. It is important in the prevention of hypoglycemia, and its inappropriate increase in diabetic patients contributes to the development of hyperglycemia.

As plasma glucose concentration increases, there is concordant increase in the filtered load of glucose. As the rate of glucose entering the nephron rises above 260-350mg/1.73m2/min (14.5-19.5mmol/1.73m2/min), the excess glucose exceeds the reabsorptive capacity of proximal tubule and is excreted in the urine (i.e. glucosuria). In health individuals this equates to a blood glucose concentration of approximately 200mg/dL (11mmol/L), which is believed to be threshold for the appearance of glucosuria. [8]


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