Question

Trace the changes in water and carbohydrate contents of the glomerulus filtrate as it passes through the renal tubules of a person suffering from diabetes mellitus.

Answer 1

There is elevated carbohydrate (glucose) contents in blood in diabetes. All of the glucose is filtered by the glomerulus and reaches renal tubules. Normally, in renal tubules (mainly PCT) all of the glucose is reabsorbed. Though there is a threshold up to which renal tubules can reabsorb glucose. In the case of elevated glucose level, renal tubules are unable to reabsorb all the glucose that passes through it. As a result, glucose starts appearing in urine (known as glycosuria).

Also, excess glucose in renal tubules develops osmotic effect. Osmotic effect decreases the reabsorption of water from renal tubules. When there is excess glucose in the blood, and it passes through the kidneys for filtering, the excess glucose accumulates in the renal tubules within the kidneys. Once there, it blocks the reabsorption of water, leading to an increased concentration of water in the filtrate which eventually leads to polyuria (excess urine formation).