Diuretics are medications that act on the kidneys to increase production of urine, and to eliminate water, certain metabolic wastes, and electrolytes from the body.
There are 5 main types of diuretics; carbonic anhydrase inhibitors, osmotic diuretics, thiazide and thiazide-like diuretics, loop diuretics, and last but not least, potassium sparing diuretics - which is the only class of diuretic that retains potassium, rather than wastes it.
Now, the basic unit of the kidney is called a nephron, and each nephron is made up of a glomerulus, which filters the blood. The filtered content goes through the renal tubule, where excess waste, and molecules such as ions and water, are removed or filtered through an exchange between the tubule and the peritubular capillaries. So the renal tubule plays a huge role in secretion and reabsorption of fluid and ions - such as sodium, potassium, and chloride - in order to maintain homeostasis - or the balance of fluid and ions in our body.
The renal tubule has a few segments of its own: the proximal convoluted tubule, the U- shaped loop of Henle, with a thin descending, a thin ascending limb, and a thick ascending limb, and finally, the distal convoluted tubule, which empties into the collecting duct, which collects the urine.
The luminal side of the proximal convoluted tubule is lined by tubule cells, which are also known as brush border cells. The apical surface of these cells, which faces the tubular lumen, is lined with microvilli. Microvilli are tiny projections that increase the cell’s surface area to help it reabsorb more solutes or water.
On the other side is the basolateral surface, which faces the interstitium, or the space between the tubule and the peritubular capillaries. When a molecule of bicarbonate approaches the apical surface of the brush border cell it binds to hydrogen to form carbonic acid. At that point, an enzyme called carbonic anhydrase type 4, which lurks in the tubule among the microvilli like a shark, swims along and splits the carbonic acid into water and carbon dioxide. The overall equation looks like this: