Water balance

• When there's too little water:

  1. The pituitary gland releases ADH
  2. ADH causes the kidney tubules to become more permeable to water
  3. this allows water to pass from the tubules into the blood
  4. because of this less urine is produced and the water levels rise back to normal.
  5. the pituitary gland stops releasing ADH.
• If the blood is too dilute:

  1. the pituitary gland stops releasing ADH
  2. the kidney tubules reabsorb less water into the blood
  3. more urine is produced and the water levels lower back to normal
• with kidney failure you must use dialysis
• 1. In kidney dialysis the patients Blood passes over a semi permeable membrane, this allows small molecules like urea, ions and water to pass through but not larger ones like protein and blood cells
  2. on the other side of the the membrane is dialysis fluid that contains the normal blood concentration, with no urea
  3. the urea passes over to the dialysis fluid
  4. the dialysis fluid is always refreshed to ensure a large concentration gradient for the urea
• Kidney dialysis is hard to maintain as they must consistently visit the hospital and have a controlled diet