Water balance

• How the hormone ADH is used to control the water level in the blood

  1. Blood becomes too concentrated

  2. Pituitary gland releases ADH

  3. ADH causes kidneys to reabsorb more water

  4. Blood water level returns to normal

  5. Pituitary gland stops releasing ADH
• How the blood becomes too dilute

  1. Blood water concentration rises

  2. Pituitary gland stops releasing ADH

  3. Kidneys reabsorb less water

  4. More urine produced

  5. Blood water concentration returns to normal
• Kidney dialysis


  Process to adjust levels of water, ions and urea when kidneys fail
• How kidney dialysis works

  1. Patient's blood passes over a semipermeable membrane

  2. Urea, ions and water pass through but not larger molecules

  3. Dialysis fluid contains normal concentrations of water and ions but no urea

  4. Urea diffuses from blood into dialysis fluid

  5. Water and ions diffuse from blood into dialysis fluid to normalise concentrations
• Kidney dialysis


  • Patients have to visit hospital several times a week
  • Patients have to eat a controlled diet
• Kidney transplant


  Diseased kidney replaced with healthy kidney from donor
• Kidney transplant


  Donated kidney may be rejected by patient's immune system
• Advantages of kidney dialysis

  • No shortage of dialysis machines
• Disadvantages of kidney dialysis

  • Inconvenient for patients
  • Patients require controlled diet
  • Expensive and requires long-term treatment
• Advantages of kidney transplant

  • Patients can lead normal life
• Disadvantages of kidney transplant

  • Shortage of donors
  • Patients have to take anti-rejection drugs for life