Water Balance and Kidney Function

Importance of Water

• Essential for life.
• Intake through drinking and eating.
• Loss through:
  • Breathing (water vapor)
  • Skin (evaporation, sweating)
  • Urine
  • Faeces

Body Fluid Regulation

• Body maintains constant concentration of internal body fluids.
• Kidneys adjust urine production based on water gained or lost.

Case Examples

• Lisa

  • Sweating profusely and no fluid intake since yesterday.
  • Extremely dehydrated.
  • Producing very little, dark urine.

• Joanne

  • Consumed lots of liquid.
  • Producing plentiful, pale urine.
  • Fully hydrated, losing excess water.

Kidney Function

• Regulates urine production to maintain blood volume and concentration.
• Blood flows in through renal artery, out through renal vein.
• Nephrons: Millions in kidney, responsible for filtering blood.
  • Fluid content of blood filtered and passed into nephron tube.
  • Right amount of water reabsorbed to adjust blood volume.
  • Remaining waste exits as urine.

Response to Drinking Water

• Lisa and Joanne's Experiment: Both drink a liter of water and give urine samples every half hour.

  • Lisa's urine gradually becomes paler, but less volume than Joanne.
  • Joanne quickly loses excess water.

• Mechanism

  • Large water intake increases body fluid.
  • Excess fluid appears in blood.
  • Kidney reabsorbs little water, most exits as urine.
  • Normalizes blood volume.

Dehydration and Kidney Response

• During dehydration, kidneys adjust reabsorption to retain water and maintain blood volume.