Diuretics 2 Flashcards
what is filtration fraction? (FF)
GFR / RPF = 0.2, thus about 20% of the plasma flowing through the glomeruli is ultrafiltered to form tubular fluid.
The thick ascending limb of the loop of Henle is the solute transport engine driving and maintaining the
counter current multiplication of interstitial solute concentration difference or solute concentration gradient extending from cortex to medulla surrounding
the collecting duct.
The early distal tubule is impermeable to water serving to further dilute the tubular fluid. However, the late distal tubule is
permeable to water when induced by an interaction with antidiuretic hormone (ADH).
Diuretics are drugs which increase the volume and rate of
urine output by decreasing the active reabsorption of solutes (saluretics) and/or water (aquaretics) in one or more segment of the nephron.
Aquaretics are drugs which decrease
the ability of ADH to increase the water permeability of the late distal tubule and collecting duct.
Lithium, fluoride (methoxy flurane) and demeclocycline are aquaretic drugs which
decrease ADH-induced water reabsorption by mechanisms not well understood.
Loop diuretics, thiazide diuretics and potassium sparing diuretics are saluretic drugs which decrease
solute reabsorption by either direct interaction with solute transport proteins in the luminal membrane or by interaction with intracellular receptors regulating
expression of solute transport proteins.
Osmotic diuretics are drugs which enter the tubular fluid by glomerular filtration and are neither
reabsorbed nor secreted along the nephron.
The presence of osmotic diuretics in the tubular fluid sufficiently increases its osmolarity to
oppose water and solute reabsorption along the nephron without specific interaction with solute transport proteins. Mannitol, excess glucose, urea and isosorbide act as osmotic diuretics when present in tubular fluid.
Diuretics change the volume and ion composition/concentration of the ECF by changing
the volume and ion composition/concentration of the urine. This is achieved primarily by decreasing reabsorption of sodium and associated ions as well as solute transport-driven, osmotically obligated water reabsorption in different segments of the nephron.
clearance is
UV / P
Free water clearance quantifies a time-dependent (rate) function of the kidney to
eliminate or retain water, free of solutes, in preserving ECF volume and osmolarity.
Sodium reabsorption in the late distal tubule and
collecting duct is regulated by circulating levels of
aldosterone which varies according to the
prevailing sodium balance.
Sodium reabsorption in the late distal tubule and
collecting duct is functionally coupled to
potassium secretion. An increase or decrease in transcellular sodium reabsorption occurs simultaneously with an increase or decrease in transcellular potassium
secretion.
In the late distal tube and the collecting tube, the functional coupling of sodium reabsorption to
potassium secretion includes the regulation of
potassium secretion by
aldosterone.