F214 Unit 4: Homeostasis

  • Created by: Saoirse
  • Created on: 09-06-14 16:34


  • Multicellular organisms need a communication system in order to:
    • Respond to changes in the internal and external environment
    • Coordinate the activities of different organs
  • Cells communicate with eachother via cell signalling. This can be
    • Hormonal
    • Neuronal
  • A good communication system will
    • Cover the whole body
    • Enable cells to communicate with eachother
    • Enable specific communication
    • Enable rapid communication
    • Enable both short-term and long-term responses


  • Homeostasis is the maintenance of the internal environment in a constant state despite external changes. Things that organisms need to maintain include:
    • Body temperature
    • Blood glucose concentration
    • Blood salt concentration
    • Water potential of the blood
    • Blood pressure
    • Carbon dioxide concentration

Negative feedback: a process that brings about a reversal of any change in conditions. It ensures an optimum steady state can be maintained. It is essential for homeostasis.

Stimulus > receptor > communication pathway (signalling) > effector > response

A number of structures are required for this pathway to work:

  • Sensory receptors e.g temp or glucose conc receptors.
    • Monitor internal conditions. If they detect a change they will be stimulated to send a message
  • A communication system e.g nervous or hormonal.
    • Used to transmot a message from the receptor cells to effectors. Message may pass through a coordination centre such as the brain.
  • Effector cells e.g. liver or muscles.
    • These bring about a response that reverses the change by the receptors.

Positive feedback

Less common that negative. Acts to increase…


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