Question

How does the presence of glucose in the nephrons result in the high volume of urine output? Why does diabetes result in high volume of urine output?

Answer 1

Urine is produced in kidney by nephrons through ultrafiltration, selective reabsorption and tubular secretion. Please understand all these three steps before you read the answer.
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Explanation:

Ultrafiltration of blood takes place at glomerulus and the filtrate accumulates in Bowman's capsule.

https://socratic.org/questions/what-is-glomerular-filtrate?source=search

The watery filtrate contains glucose along with other solutes. When blood glucose level is very high (above 180mg/dL), as happens in case of diabetic patients, more glucose enters filtrate: and subsequently 100% reabsorption of glucose by renal tubules will not be possible. Hence glucose will appear in urine. This is because renal threshold of glucose is 180mg/100ml of blood.

Presence of extra solute (i.e. glucose) in tubular filtrate would prevent water to leave, i.e. there will be less reabsorption of water along descending loop of Henle . This water is excreted with urine. Hence dilute and more voluminous urine (=diurea) is produced when glucose is excreted.