F214 Unit 4: Homeostasis

Communication:

• 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

• 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…