Question

People suffering with diabetes mellitus produce unusually large volumes of urine frequently. They also have much higher urine osmolarity than healthy individuals. Explain why increased urine volume and osmolarity are characteristics observed in diabetics. (include nephron loop function, especially descending limb)

Answer 1

Diabetes mellitus is characterised by high levels of glucose in blood.
When this blood enters the kidney for filtration, initially the afferent arterioles undergoes vasodilation and increased rate of filtration. As the load on kidneys increase due to higher filtration rates renal hypertension develops. This causes damage to the endothelium of glomeruli, podocytes and basement membrane. This results in renal tubulo interstitial injury which impairs the reabsorption of glucose. Damage to podocytes and glomeruli also increases loss of proteins of the blood into urine. The proximal tubule and descending limb of henle are permeable to water. Injury to the wall of proximal tubule and descending results in increased permeability of water.
The loss of proteins into urine makes the urine osmotic while loss of water from proximal tubules and descending limb results in increased urine output.
This is the reason behind osmotic Polyuria in diabetes patients.