Multiple choice

Which of the following is characterised by low plasma osmolality?

  1. SIADH

  2. Addison's disease

  3. Cranial diabetes insipidus

  4. Nephrogenic diabetes insipidus

  5. Central diabetes insipidus
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In nephrogenic diabetes insipidus, there is adequate ADH, but the kidney is unable to respond to the ADH. Nephrogenic diabetes insipidus can arise as a side effect of certain drugs, especially lithium which is used to treat manic depression. Changes in plasma osmolality are poorly tolerated, especially by nerve cells, so plasma osmolality is tightly regulated. If renal water reabsorption is inadequate then there will be excess water loss in the urine and plasma osmolality will rise and vice versa. Central diabetes insipidus is characterised by low plasma osmolality.

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