A patient is told by their doctor that their pituitary gland has stopped producing ADH. Explain what effect this would have on the patient's kidneys and the composition of their urine.

WJEC A-Level Biology (Wales) — 4.5 Homeostasis and the kidney · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

ADH normally increases the permeability of the kidney tubules to water. Without ADH the tubules remain less permeable, so water is not reabsorbed. Consequently a larger volume of urine is produced and the urine is more dilute, containing more water. The patient may become dehydrated because water is lost in the urine rather than retained in the blood.

Examiner tips

  • Use the term "ADH" and "pituitary gland" to show understanding of the system.
  • Explain the chain: lack of ADH → reduced water reabsorption → increased urine volume and dilution.
  • Mention dehydration as a physiological consequence.
  • Keep the answer concise and use the exact wording from the mark scheme.

Common mistakes

  • Confusing ADH with other hormones such as vasopressin or renin.
  • Failing to state that the urine becomes more dilute or that water is not reabsorbed.
  • Omitting the link to dehydration or the effect on urine volume.

Mark scheme (5 marks)

  1. ADH normally increases the permeability of the kidney tubules to water
  2. Without ADH, the kidney tubules remain less permeable to water / water is not reabsorbed
  3. A larger volume of urine is produced
  4. The urine produced is more dilute / contains more water
  5. The patient may become dehydrated because water is lost in the urine rather than being retained in the blood

Key terms in this question

ADH · pituitary gland · urine

Related

More Homeostasis and the kidney questions

▶ Try answering this question with AI marking (free) →