Pediatric emergency medicine trisk 1890 1890
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a water channel (aquaporin) into the luminal membrane of the collecting duct and allowing
water reabsorption along the medullary concentration gradient. Lack of ADH (central DI) can
result from a wide variety of hypothalamic and pituitary lesions ( Table 89.7 ).
In nephrogenic DI, ADH levels are normal or elevated because the defect resides in the
renal collecting tubules, which are resistant to the action of ADH. In either case, failure of
water reabsorption results in polyuria. A normal thirst mechanism contributes toward fluid
balance by promoting adequate fluid intake; however, if this balance is not achieved,
hypertonic dehydration ensues. If a hyperosmolar state develops abruptly, it may lead to
dehydration of neural tissues, which can cause serious neurologic sequelae or result in death.
The pons is particularly sensitive to this effect resulting in central pontine myelinolysis.
