Osmotic Diuretics B

Agents: mannitol, sorbitol. Site of action: mainly the proximal tubules. Mode of action: Since NaCl and H2O are reabsorbed together in the proximal tubules, Na+ concentration in the tubular fluid does not change despite the extensive reabsorption of Na+ and H2O. Body cells lack transport mechanisms for polyhy-dric alcohols such as mannitol (structure on p. 171) and sorbitol, which are thus prevented from penetrating cell membranes. Therefore, they need to be given by intravenous infusion. They also cannot be reabsorbed from the tubular fluid after glomerular filtration. These agents bind water osmotically and retain it in the tubular lumen. When Na ions are taken up into the tubule cell, water cannot follow in the usual amount. The fall in urine Na+ concentration reduces Na+ reabsorption, in part because the reduced concentration gradient towards the interior of tubule cells means a reduced driving force for Na+ influx. The result of osmotic diuresis is a large volume of dilute urine.

Indications: prophylaxis of renal hypovolemic failure, mobilization of brain edema, and acute glaucoma.

Osmotic Diuretics MechanismMode Action Osmotic Diuretics

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  • Freddy
    How antidiuretic hormone work on dilute conc urine?
    8 years ago
  • aino suomi
    Why a diuretic might be given to someone who has edema?
    8 years ago

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