homeostasis

• Homeostasis


  the maintenance of a constant internal environment. It involves control systems that keep your internal environment roughly constant (within certain limits). Keeping your internal environment constant is vital for cells to function normally and to stop them being damaged.
• • if the temperature of metabolic reactions increases too much the reaction essentially stops
  • The rise in temperature makes the enzyme's molecules vibrate more.
  • If the temperature goes above a certain level, this vibration breaks some of the hydrogen bonds that hold the enzyme in its 3D shape.
  • The active site changes shape and the enzyme and substrate no longer fit together.
  • At this point, the enzyme is denatured - it no longer functions as a catalyst
• If body temperature is too low enzyme activity is reduced, slowing the rate of metabolic reactions. The highest rate of enzyme activity happens at their optimum temperature
• Negative feedback

  • Receptors detect when a level is too high or too low, and the information's communicated via the nervous system or the hormonal system to effectors.
  • The effectors respond to counteract the change - bringing the level back to normal.
  • The mechanism that restores the level to normal is called a negative feedback mechanism
• negative feedback mechanism

  A) receptors

  B) nervous

  C) hormonal

  D) effectors

  
• Negative feedback only works within certain limits though - if the change is too big then the effectors may not be able to counteract it, e.g. a huge drop in body temperature caused by prolonged exposure to cold weather may be too large to counteract.
• • Some changes trigger a positive feedback mechanism, which amplifies the change.
  • The effectors respond to further increase the level away from the normal level.
  • The mechanism that amplifies a change away from the normal level is called a positive feedback mechanism
• Positive feedback isn't involved in homeostasis because it doesn't keep your internal environment constant. Positive feedback is useful to rapidly activate processes in the body.
• positive feedback

  A) receptors

  B) nervous

  C) hormonal

  D) effectors

  E) amplified