Mannitol is a sugar that is filtered, but not reabsorbed, by the kidneys. What effect would drinking a solution of mannitol have on the volume of urine produced?

Verified step by step guidance

1. Understand the role of mannitol in the kidneys: Mannitol is filtered by the glomerulus but is not reabsorbed in the renal tubules, meaning it remains in the tubular fluid.
2. Recall that substances remaining in the tubular fluid increase its osmolarity, which affects water reabsorption by osmosis.
3. Since mannitol stays in the tubules, it creates an osmotic gradient that prevents water from being reabsorbed back into the bloodstream, leading to more water remaining in the urine.
4. This osmotic effect causes an increase in urine volume, a process known as osmotic diuresis.
5. Therefore, drinking a mannitol solution would increase the volume of urine produced by reducing water reabsorption in the kidneys.

Key Concepts

Glomerular Filtration

Glomerular filtration is the process by which blood plasma is filtered through the glomeruli in the kidneys, allowing water and small molecules like mannitol to pass into the renal tubules while retaining larger molecules and cells in the bloodstream.

Tubular Reabsorption

Tubular reabsorption is the process where substances filtered into the renal tubules are selectively reabsorbed back into the bloodstream. Since mannitol is not reabsorbed, it remains in the tubules, affecting water movement.

Osmotic Diuresis

Osmotic diuresis occurs when non-reabsorbed solutes like mannitol increase the osmolarity of the tubular fluid, preventing water reabsorption and leading to increased urine volume as water follows the solute into the urine.