This results in an increased excretion of these ions in the urine. Water reabsorption is also reduced because it is dependent upon sodium reabsorption. Therefore, there is an increase in water excretion in the urine as well. There are five main classes of diuretics. Osmotic diuretics are substances that are freely filterable at the glomerulus but are not easily reabsorbed by the tubules.
Examples are urea, glycerol, and mannitol.
These osmotic diuretics primarily work on the proximal convoluted tubule, and remain in the lumen and increase the osmotic pressure, thereby impeding the osmotic withdrawal of water from the filtrate, resulting in an increased volume of urine. Loop Diuretics , example furosemide, act on the thick ascending limb of the loop of Henle and inhibit sodium chloride transport in the luminal membrane, thereby causing retention of water in the tubular lumen. This results in an increased volume of urine. Carbonic Anhydrase Inhibitors , example acetazolamide, block bicarbonate reabsorption in the proximal tubules by inhibiting the enzyme, carbonic anhydrase, that is attached to the lumen of the tubular epithelial cells. Carbonic anhydrase catalyzes the dissociation of carbonic acid into water and carbon dioxide.