# Explain how the body detects a drop in blood water concentration and responds to restore normal water balance.

> Eduqas A-Level Biology — 4.5 Homeostasis and the kidney · Explain · 5 marks

> The body constantly monitors and adjusts its internal conditions. One important variable that is regulated is the water concentration of the blood.

## Mark scheme (5 marks)

1. The hypothalamus detects the drop in blood water concentration (acts as a receptor / monitors blood water concentration)
2. The pituitary gland secretes / releases more ADH (into the bloodstream)
3. ADH travels in the blood(stream) to the kidneys (as its target organ)
4. ADH increases the permeability of the kidney tubules / collecting duct to water, so more water is reabsorbed (back into the blood)
5. A smaller volume of more concentrated urine is produced, restoring blood water concentration to normal (homeostasis / negative feedback)

## Related

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