6.4.1 Principles of homeostasis

• Describe homeostasis in mammals

  ● Maintenance of a stable internal environment within restricted limits

  ● By physiological control systems (normally involve negative feedback)
• Explain the importance of maintaining stable core temperature

  • If temperature is too high:
  • Hydrogen bonds in tertiary structure of enzymes break
  • tertiary structure changes shape
  • Enzymes denature; active sites change shape and substrates can’t bind
  • So fewer enzyme-substrate complexes
  • If temperature is too low:
  • Not enough kinetic energy so fewer enzyme-substrate complexes
• Explain the importance of maintaining stable blood pH

  • Above or below optimal pH, ionic / hydrogen bonds in tertiary structure break
  • tertiary structure changes shape
  • Enzymes denature; active sites change shape and substrates can’t bind
  • So fewer enzyme substrate complexes
• Explain the importance of maintaining stable blood glucose concentration

  Too low (hypoglycaemia)

  ● Not enough glucose (respiratory substrate) for

  respiration

  ● So less ATP produced

  ● Active transport etc. can’t happen → cell death

  Too high (hyperglycaemia)

  ● Water potential of blood decreases

  ● Water lost from tissue to blood via osmosis

  ● Kidneys can’t absorb all glucose → more water

  lost in urine causing dehydration
• Describe the role of negative feedback in homeostasis

  1. Receptors detect change from optimum

  2. Effectors respond to counteract change

  3. Returning levels to optimum / normal
• Explain the importance of conditions being controlled by separate

  mechanisms involving negative feedback

  ● Departures in different directions from the original state can all be controlled / reversed

  ● Giving a greater degree of control (over changes in internal environment)
• Describe positive feedback

  1. Receptors detect change from normal

  2. Effectors respond to amplify change

  3. Producing a greater deviation from normal