maintaning water & nitrogen balance in the body

• what is osmosis?

  movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• how is water lost from the body?

  • exhalation via lungs
  • sweating
  • urine
• how are ions lost from the body?

  • sweating
  • urine
• what happens if body cells loose or gain too much water from osmosis?

  they won't function efficiently
• how are excess amino acids excreted from the body?

  • deanimated in the liver to form ammonia
  • ammonia is toxic, therefore it is converted to urea
  • urea is excreted from the body via sweat & urine
• how do kidneys produce urine?

  • filter blood in order to remove waste substances e.g. urea
  • reabsorb useful molecules e.g. glucose, water, ions
• where is ADH secreted in the body?

  pituitary gland in the brain
• how does ADH affect the reabsorption of water in the kidneys?

  • when blood is too concentrated, pituitary gland secretes more ADH
  • ADH travels in the bloodstream to the kidney & increases the permeability of kidney tubules to water
  • more water is reabsorbed in the kidney, resulting in a smaller volume of more concentrated urine
• how can kidney failure be treated?

  • dialysis
  • transplant
• how does kidney dialysis work?

  • a specialist machine carries out the function of the kidneys
  • persons blood flows through partially permeable membranes, surrounded by dialysis fluid
  • membranes are permeable to ions & waste substances but not big molecules like proteins
  • dialysis contains the same concentration of glucose & ions as healthy blood
  • only excess & waste molecules are removed from the blood, glucose & ions remain
• advantages of kidney dialysis

  patient lives longer until a donor organ is found
• disadvantages of kidney dialysis

  • patient has to visit hospital frequently, long sessions
  • can cause blood clots & infections
  • expensive
• advantages of kidney transplant

  • doesn't require repeated visits to the hospital - flexible lifestyle
  • cheaper in the long run
  • doesnt need a controlled diet
• disadvantages of kidney transplant

  • shortage of donors - have to wait long
  • risk of infection from surgery
  • have to take immunosuppressant drugs for life