Positive Feedback

• What do some changes trigger?

  a positive feedback mechanism
• what do positive feedback mechanisms do?


  Amplify a change from the normal level
• What do the effectors do?


  Respond to further increase the level AWAY from the NORMAL LEVEL
• what is positive feedback useful for?


  Useful to rapidly activate something eg a blood clot after an injury
• EXAMPLE: activating a blood clot after an injury?

  1. Platelets become activated & release a CHEMICAL - this triggers more platelets to be activated and so on
  2. Platelets very quickly form a blood clot at injury site
  3. The process ENDS WITH NEGATIVE FEEDBACK , when the body detects blood clot has formed
• When can positive feedback occur?


  • to rapidly activate something
  • when a HOMEOSTATIC SYSTEM BREAKS DOWN
• Example of positive feedback used when a homeostatic system breaks down?


  Hypothermia (Low body temp - below 35c)

  1. hypothermia occurs when heat is lost from the body quicker than it can be produced
  2. as body temp falls the brain does not work properly and SHIVERING STOPS - makes body temp decrease further
  3. +ive feedback takes body temp further away from normal level, and it continues to decrease unless action is taken
• what is positive feedback not involved in?

  homeostasis
• Why is positive feedback not included in homeostasis?


  it does not keep your internal environment stable