# Explain how the urinary system and the cardiovascular system are integrated to maintain water balance in the body.

> IB DP Biology Standard Level (2023 syllabus) — C3.1 Integration of body systems · Explain · 4 marks

## Mark scheme (4 marks)

1. The kidneys (as part of the urinary system) filter blood delivered by the cardiovascular system, receiving blood via the renal arteries.
2. Specialised receptors (osmoreceptors) in the hypothalamus detect changes in blood osmolarity / water potential of the blood.
3. ADH (antidiuretic hormone) is released from the posterior pituitary and travels via the bloodstream (cardiovascular system) to the kidneys.
4. ADH increases the permeability of the collecting ducts to water, so more water is reabsorbed into the blood, reducing urine output and restoring blood osmolarity / water balance.

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