An osmotic diuretic
is a type of diuretic
that inhibits reabsorption of water and sodium. They are pharmacologically inert substances that are given intravenously. They increase the osmolarity of blood and renal filtrate.
Two examples are mannitol
In the nephron
, osmotic diuretics act at the portions of the nephron that are water-permeable.
Osmotic diuretics works by expanding extracellular fluid and plasma volume, therefore increasing blood flow to the kidney
. This washes out the cortical medullary gradient
in the kidney. This stops the loop of Henle
from concentrating urine, which usually uses the high osmotic and solute gradient to transport solutes and water.
These agents can also act at other parts of the body. For example, they can be used to reduce intracranial and intra-ocular pressure.
Physiological working of osmotic diuretics
The renal proximal tubule
is the primary site of action of osmotic diuretics.
Normally, water molecules follow Na<sup>+</sup> out of the proximal tubule, resulting in Na<sup>+</sup> and water reabsorption. When osmotic diuretics are introduced, they hold onto water molecules in the tubule. Since the luminal membrane
is quite leaky to Na<sup>+</sup>, this causes a high back leak of Na<sup>+</sup>... Read More