B1 Topic 2

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Homeostasis = Maintaining a stable internal environment

Osmoregulation = Regulating water content - balance the amount gained and lost

Thermoregulation = Regulating body temperature - get rid of excess heat but retain when cold

Blood glucose regulation = Keep glucose in the blood at a steady level

A mechanism called negative feedback helps keep things steady:

  • Changes in environment trigger a response that counteracts the changes
  • So internal environment stays at a norm
  • Only works with certain limits
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Homeostasis ctnd...


  • Part of the brain that cotrols body temperature
  • Contains receptors that are sensitive to the blood temp of brain
  • Receives impulses from receptors in skin proving info about skin temp.
  • Hypothalamus detects a change and causes a response in the dermis (deep layers of skin)


  • Erector muslces relax, hairs lie flat
  • Lots of sweat to cool you down
  • Blood vessels close to the surface of skin dilate (VASODILATION)
  • More blood can flow to surface to trasnfer heat to surroundings.


  • Erector muscles contract, hairs stand on end to trap insulating layer of air
  • Very little sweat
  • Blood vessels near surface of skin constrict (VASOCONSTRICTION)
  • Less blood flows near surface so less heat is transferred to surroundings
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  • Chemical messengers which travel in the blood to activate target cells.
  • Produced in various glands called ENDOCRINE glands
  • Released into the blood to be carried to parts of the body
  • Travel all over the body but only affect particular cells
  • The affected cells are called target cells - they've the right receptors to respond to hormone
  • An organ that contains target cells is called a target organ
  • Travel at the speed of blood
  • Long-lasting effects
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