Importance of Water for the Body

• Essential for Life: Water is crucial for survival as it is ingested through drinking and eating.
• Loss of Water:
  • Evaporation: Water vapor is lost through breathing and skin evaporation.
  • Sweating: Noticeable water loss when sweating.
  • Urine and Feces: Water is also lost via these.

Body's Regulation of Water

• Constant Concentration Maintenance: Despite daily fluctuations, the body maintains fluid concentration.
• Role of the Kidneys:
  • Urine Production: Adjusts urine output based on water intake and loss.
  • Fluid Balance: Kidneys ensure blood is at a constant volume and concentration.

Case Studies: Lisa and Joanne

Lisa's Situation

• Current State: Dehydrated due to lack of water intake.
• Urine Production: Little urine that is dark due to dehydration.

Joanne's Situation

• Current State: Fully hydrated from high water intake.
• Urine Production: Plentiful and pale urine indicating excess water is being expelled.

Function of the Kidneys

• Blood Flow:
  • Renal Artery & Vein: Blood enters through the renal artery and exits via the renal vein.
• Nephrons:
  • Filtration: Blood is filtered and fluid content enters the nephron.
  • Water Reabsorption: Correct water amount reabsorbed to maintain blood volume.
  • Urine Formation: Waste solution exits as urine.

Experiment: Lisa and Joanne's Water Intake

• Water Intake Experiment: Both drink a liter of water and provide urine samples every half hour.
• Results:
  • Lisa: Urine becomes paler but less than Joanne's.
  • Joanne: Loses most water quickly; kidneys expel excess fluid.

Dehydration and Kidney Function

• Dehydrated State: Minimal water reabsorption and low, concentrated urine output to conserve water.
• Excess Fluid: If overhydrated, excess fluid enters the blood and is expelled, normalizing blood volume.