Maintaining water balance

• If there ISNT ENOUGH water in blood (eg. Due to sweating) the PITUITARY GLAND releases hormone ADH into bloodstream.

  • ADH travels to kidneys and causes kidney tubes to become more PERMEABLE to water so more water can pass OUT of kidneys INTO blood

  - when enough water is in blood again the pituitary gland stops producing ADH (NEGATIVE FEEDBACK)
• If blood has TOO MUCH water

  • PITUITARY GLAND stops releasing ADH - kidneys RE-ABSORB the water OUT of blood through permeable kidney tubes
• KIDNEY DIALYSIS (blood contains a HIGHER amount of WATER/UREA/IONS than it should)

  • patients blood passes over SEMI-PERMEABLE membrane (allows only urea/water/ions through and not larger molecules like blood cells/ proteins)

  - Dialysis fluid contains normal concentrations of water and ions but NO UREA so only some water and ions diffuse but not all

  - UREA diffuses from blood into dialysis fluid and levels return normal
• kidney transplant +\-

  + allows patient to live normal life / expensive initially. - shortage of kidney donors and rejection and take anti rejection drugs for rest of life
• Dialysis +\-

  • + - no shortage of dialysis machines
  • . - - frequent treatments and controlled diet / expensive long term