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Internal conditions in the human body must be controlled.

There are lots of things to control including

  • Water
  • C02
  • Oxygen
  • Ions (like salt)
  • Sugar levels
  • Temperature

Various parts of our body are fashioned to deal with all this and when conditions aren't right - our bodies respond.


Water enters our body through food and drink. It is lost through.

  • Sweat
  • Breathing
  • Urine

Water balance depends on the day's temperature.

 COLD: No sweat, more urine.Dilute.
HOT: More sweat, less urine.  Concenerature and skin response

Too HOT:

  • Hair flat to remove insulating layer of air
  • Lots of sweat too transfer heat to the environment and cool you down
  • Blood vessels under skin widen
    • vasodilation - more blood flows near surface. Heat is radiated away and you are cooled down
  •  Brain encourages you to take off layers


  • Hair stands up providing insulating air layer
  • Very little sweat
  • Blood vessels constrict to retain heat vasoconstriction
  • Shiver to generate heat
  • Brain encourages to put on layers


The kidney is responsible for taking care of our ion content.

  • Taken in when we eat food
  • Excess which needs to be removed
  • Kidneys remove excess ions from…


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