Maintaining Body's water balance

• what happens if the blood becomes concentrated i.e the level of water in the blood falls?

  the pituitary gland releases a hormone ADH into the bloodstream
• how is water levels maintained if blood becomes too concentrated?

  1. ADH travels to the kidneys
  2. causes the kidney tubules to become more permeable to water ( more H20 can pass out of the tubules)
  3. more water is reabsorbed from the tubules back into the blood
  4. less urine is produced and the amount of H20 in blood rises to its normal level
  5. pituitary gland stops releasing ADH
• role of the ADH?

  causes the kidneys to reabsorb more water to maintain normal water levels
• what happens if the blood becomes too dilute?

  1. concentration of H20 in blood increases = PG stops releasing ADH
  2. kidneys reabsorb less water into the blood
  3. more urine is produced and conc of H20 in blood returns to normal
• how does kidney dialysis work?

  1. patients blood passes through a semi-permeable membrane= allows ions, mineral, glucose through but not proteins as they are big
  2. the dialysis fluid contains normal conc of H20 and ions (no urea) = some H20 and ions will diffuse from blood into dialysis fluid = blood returns to normal
  3. urea diffuses from the blood into the dialysis fluid = constantly refreshed = larger conc gradient for urea
• disadvantages of kidney dialysis?

  -patients visit the hospital several times a week

  -controlled diet = dont produce too much urea

  -dialysis may cause blood clots / infections

  -expensive for NHS and expensive in the long term
• advantage of kidney dialysis?

  buys valuable time for patients until a donor comes
• disadvantages of kidney transplant?

  -risk of infections and blood clots

  -surgery is always risky

  -donor takes a long time to find a match

  -donor can be rejected by immune system

  -expensive initially

  -patients take immunosuppressant drugs for the rest of their life = prevents rejection of kidney
• advantages of kidney transplant?

  -allows patient to live a normal life

  -pernament fix

  -don't need to be in and out of hospitals