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The intestinal and renal tubular epithelia Post Date: Thu, 16 Oct 2008 6:36:50 +0000 As the glu-cose concentration is increased in both the plasma and the filtrate, the threshold and total reabsorptive capacity of the transport mechanism are exceeded and glucose ap-pears in the voided urine. Hence, with severe hyperglycemia, glucose acts as an osmotic diuretic, even though a portion of the amount filtered continues to be reabsorbed.The intestinal and renal tubular epithelia have many permeability characteristics in common. Autor of the post: Undefined However, urea is absorbed Post Date: Thu, 16 Oct 2008 6:19:31 +0000 Most osmotic diuretics, which, by definition, are poorly reabsorbed by the renal tubules, are also not absorbed from the gas-trointestinal tract. Thus, these agents must be administered parenterally in order to achieve effective plasma concentrations. However, urea is absorbed from the intestine. Autor of the post: Undefined Their uses include prophylaxis against Post Date: Thu, 16 Oct 2008 6:00:35 +0000 Therapeutic Uses. Osmotic diuretics may be used for several purposes that are distinct and separate, but all of which depend on the same fundamental characteristics. Their uses include prophylaxis against acute renal failure, differential diagnosis of acute oliguria, and reduction of cerebrospinal and intraocular fluid pressures. Autor of the post: Undefined Perhaps one of the clearest Post Date: Thu, 16 Oct 2008 5:45:21 +0000 Although urea and glu-cose have been employed in the past as oral diuretics for the treatment of chronic edema, they have been replaced by superior agents.Mannitol is extensively employed. Perhaps one of the clearest and most important indications is the prophylaxis of acute renal failure. Autor of the post: Undefined The latter may Post Date: Thu, 16 Oct 2008 5:30:48 +0000 It is used for this purpose in conditions as diverse as cardiovascular operations, severe traumatic injury, operations in the presence of severe jaundice, and management of hemolytic transfusion reactions. In each of theseconditions, a precipitous fall in urine flow may be anticipated either as the result of an acutely reduced filtration rate or from acute changes in tubular per-meability. The latter may be the consequence of the presence of a noxious agent within the tubular fluid in excessively high concentrations, in some instances sufficient to result in actual precipitation. Autor of the post: Undefined Many of the mechanisms responsible Post Date: Thu, 16 Oct 2008 5:13:19 +0000 In these situations, mannitol exerts an osmotic effect within the tubular fluid, inhibits water reabsorption, and maintains the rate of urine flow within reasonably normal limits. As a consequence, the concentration of the noxious agent within the tubular fluid does not reach the excessively high levels that otherwise would have been achieved by the more complete reabsorption of water. Many of the mechanisms responsible for nephrotoxicity are incompletely un-derstood. Autor of the post: Undefined Additional factors may also Post Date: Thu, 16 Oct 2008 4:55:15 +0000 However, it is clear that under these condi-tions the use of osmotic diuretics protects the kidney against damage. The maintenance of an adequate flow of relatively dilute urine is probably the single most important factor. Additional factors may also be involved. Autor of the post: Undefined Despite the fact that these Post Date: Thu, 16 Oct 2008 4:44:42 +0000 In the presence of hypotension mannitol is more effective than saline solution in maintaining glomerular filtration (Morris et ah, 1972). If given in sufficiently large amounts, mannitol increases extracellular osmolality, which in turn may decrease cellular swelling and improve renal blood flow (Flores et al, 1972). Despite the fact that these mechanisms have been demonstrated experimentally, their clinical significance remains to be evaluated. Autor of the post: Undefined However, if either glomerular Post Date: Thu, 16 Oct 2008 4:33:33 +0000 A closely related but separate use of mannitol is in the evaluation of acute oliguria. With a partial reduction in glomerular function, as might occur from excessive loss of body fluids, urine flow may be increased toward normal by the administration of an osmotic diuretic, and this response may serve as a guide for the additional administration of parenteral fluids. However, if either glomerular or tubular function is too severely compromised, mannitol will not increase urine flow. Autor of the post: Undefined By elevating the osmolality Post Date: Thu, 16 Oct 2008 4:18:37 +0000 This may help orient the further management of the patient with acute anuria (Barry and Malloy, 1962).Mannitol is also used for the reduction of the pressure and volume of the intraocular and cerebro-spinal fluids. By elevating the osmolality of the plasma, one is able to enhance the diffusion of water from those fluids back into the plasma and the ex-tracellular space. 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