Patients with Diabetes Mellitus Have Frequent Urination and Increased Thirst

Question

Patients with diabetes mellitus have frequent urination and increased thirst because
A)less water passes from the glomerulus to the glomerular capsule.
B)more water is driven from the glomerulus to the glomerular capsule than normal.
C)more salt is reabsorbed at the proximal convoluted tubule.
D)an increase in sodium ions causes more nerve stimulation and triggers urination.
E)increased glucose in the urine increases its osmolarity and less water is reabsorbed by blood.

Accepted Answer

In diabetes mellitus, blood glucose levels are elevated and therefore glucose is filtered into the nephron where it is normally reabsorbed in the proximal tubule. However, because of the high levels of glucose, the reabsorptive capacity is exceeded and some glucose stays in the urine. Glucose is an osmotic solute and therefore increases the osmotic pressure of the filtrate, which leads to less water being reabsorbed from the filtrate back into the bloodstream. This results in increased urine production and thirst.