Kidneys

• Osmosis - diffusion of water from dilute solution to concentrated solution through partially permeable membrane
• if blood is too dilute - water moves INTO cells by osmosis

  if blood is too concentrated - water moves OUT of cells by osmosis
• Loosing water in body

  • by lungs when we exhale ( body cant control how much water is lost by this )
  • sweating ( body cant control water lost by this )
  • by kidneys in urine ( body can control how much water is lost in urine)
• If blood is too dilute

  • kidneys remove excess water ( and excess ions) and produce more urine
• blood enters kidney through artery and that blood contains waste product UREA

  • kidney removes the urea and excess water/ions
  • these leave kidney as URINE and is stored in BLADDER
  • the clean blood now leaves the kidney through a VEIN
• in kidneys -

  • blood passes through CAPILLARIES from artery and small molecules (urea/water/ions/glucose) are filtered OUT into a tube
  • the tube has glucose (which ALL of it is re absorbed) /ions/water and a certain amount is reabsorbed back into blood if levels not right (SELECTIVE REABSORPTION)
  • ALL urea and excess water/ions are released as urine
• In kidneys-

  • ALL urea removed
  • concentrations of water/ions have been adjusted depending on levels
  • glucose is filtered then all is reabsorbed so levels stay the same
• Proteins - long chains of amino acids
• Excess amino acids -

  • liver breaks down amino acids and produces AMMONIA ( this process called DEAMINATION )
  • ammonia is very toxic so the liver converts it to urea and urea can safely be excreted by kidneys