Why does polyuria occur with diabetes mellitus?

Answer 1

I think you mean polyuria instead of polyurea. Polyuria is a medical term used to describe the symptom of increased frequency of urination. When glucose levels in blood are greater than normal, the molecule of glucose 'leaks' into the urine. As glucose enters the urine, it brings water molecules with it and, in turn, urine volume increases and, 'voila', polyuria happens..

Answer 2

Diabetes Mellitus is characterised by chronic hyperglycaemia due to absolute loss of insulin (Type I) or a resistance to it (Type II) . Insulin receptors normally allow glucose to enter each cell from the blood. Without insulin being received, the glucose meant for the cells remains trapped in the blood.

Thus in a diabetic, we have too much glucose in the blood (hyperglycaemia). Beyond a certain level of excess, the glucose becomes dangerous in the blood and is therefore extracted by the kidneys and ends up in the urine.

As the urine is loaded with extra glucose it becomes more concentrated. Osmotic pressure pulls extra water into the urine to keep its concentration closer to that of the surrounding tissue, leading to higher volume of urine.

Hence polyuria (increased volume of urine) is experienced by the diabetic.