# Explain how the body responds to a rise in blood osmolarity, such as that caused by excessive sweating during prolonged exercise.

> IB DP Biology Standard Level (2023 syllabus) — D3.3 Homeostasis · Explain · 4 marks

## Mark scheme (4 marks)

1. Osmoreceptors in the hypothalamus detect the rise in blood osmolarity
2. The posterior pituitary gland releases ADH (antidiuretic hormone) into the blood
3. ADH increases the permeability of the collecting ducts (and distal convoluted tubule) to water
4. More water is reabsorbed by osmosis into the blood, producing a smaller volume of more concentrated urine, which restores blood osmolarity to normal (negative feedback)

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-body-responds-to-a226eb4e) · Published by Druglandscape Ltd.