Water Balance

Water loss occurs through:

  • Sweating (skin evaporation)

  • Respiration (breathing)

  • Urine (kidney excretion)

  • Faeces (large intestine excretion)

 

Negative Feedback Regulation of Water Balance:

  1. Stimulus – Water loss increases solute concentration in blood (dehydration), raising osmolarity.

  2. Receptor – Osmoreceptors in the hypothalamus detect this.

  3. Control Centre – The hypothalamus signals the pituitary gland to release antidiuretic hormone (ADH).

  4. Effector – ADH triggers the kidneys to reabsorb more water from urine back into the bloodstream.

  5. Outcome – Water balance is restored, ADH production reduces (feedback loop stops).

 

Gaining & Retaining Water:

  • When extracellular fluid (ECF) has excess water, it dilutes solutes.

  • The hypothalamus detects this and reduces ADH secretion.

  • Thirst is switched off, preventing overhydration.