Osmotic diuretics primarily act on which part of the nephron?

Osmotic diuretics primarily act on the glomerulus. These agents, such as mannitol, increase the osmolarity of the filtrate in the renal tubules, leading to an increased volume of fluid that is retained in the nephron. The principal mechanism of action occurs at the level of the glomerulus where they expand plasma volume and increase renal blood flow, which enhances the glomerular filtration rate (GFR). This results in increased urine output as more fluid and solutes are filtered into the nephrons.

The effectiveness of osmotic diuretics is characterized by their ability to draw water into the tubular lumen, preventing reabsorption and promoting diuresis. Although they do influence other parts of the nephron by affecting fluid reabsorption, their primary site of action is considered to be in the glomerulus where their osmotic effects can initially impact the filtration process.