Kidneys

• Water is essential to keep the body functioning, so the amount of water in the blood (and so the ψ of the blood) needs to be KEPT CONSTANT
• What do mammals excrete?

  Urea & other waste products - in SOLUTION = water lost during excretion.
• How is water lost?

  • excretion
  • in sweat
• What do the kidneys do


  • Regulate the ψ of the blood (and urine) so the body has the right amount of water = OSMOREGULATION
• What happens if the ψ of the blood is TOO LOW?


  • Too low (body is dehydrated):
  • More water reabsorbed by osmosis into the blood from the tubules of the nephrons
  • this means urine is more concentrated , so less water is lost during excretion
• What happens if the ψ of the blood is TOO HIGH?


  ψ of blood too high (body is too hydrated):

  • less water reabsorbed by osmosis into the blood from the tubules of the nephrons
  • = urine is more dilute = MORE water LOST DURING EXCRETION
• Water is reabsorbed into the blood along ...


  along almost all of the nephron , but regulation of ψ mainly takes place in the loop of Henle, DCT and collecting duct
• What do hormones control?


  The volume of water reabsorbed by the DCT and collecting duct