# Explain how the body uses ADH to respond when a person becomes dehydrated after exercising on a hot day.

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

> During exercise on a hot day, a person loses water through sweating. This causes the water content of the blood to fall below the optimum level.

## Mark scheme (5 marks)

1. The hypothalamus detects the fall in water content of the blood (acts as a receptor / monitors blood water concentration).
2. The pituitary gland secretes / releases more ADH into the bloodstream.
3. ADH travels in the bloodstream to the kidney (tubules / collecting duct).
4. ADH makes the kidney tubules / collecting duct more permeable to water.
5. More water is reabsorbed back into the blood, so a smaller volume of more concentrated urine is produced, restoring water balance / homeostasis.

## Key terms

- [ADH](https://www.gradenine.co.uk/glossary/adh)

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-body-uses-adh-85822fe1) · Published by Druglandscape Ltd.