6.4.1 principles of homeostasis and negative feedback

• 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,refer to high temperature only?

  ● If temperature is too high:

  ○ Hydrogen bonds in tertiary structure of enzymes break

  ○ Enzymes denature; active sites change shape and substrates can’t bind

  ○ So fewer enzyme-substrate complexes
• Explain the importance of maintaining stable core temperature, refer to low temperature only?

  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

  ● 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, refer to too low blood glucose only?

  too low is known as hypoglyceamia

  ● Not enough glucose (respiratory substrate) for

  respiration

  ● So less ATP produced

  ● Active transport etc. can’t happen → cell death
• Explain the importance of maintaining stable blood glucose concentration, refer to too high blood glucose only?

  too high is known as - 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

  Examples: control of blood glucose, concentration, blood pH, core

  temperature and blood water potential
• 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

  Not involved in homeostasis.

  Examples: onset of contractions in childbirth, blood clotting
• common exam mistakes on this topic

  mistake: *Using generalised statements about positive feedback when explaining why information given is an example of positive feedback.*

  Explanation: You need to use the information provided. For example,

  [named molecule 1] causes more [named molecule 2] to be formed, which in turn causes more [named molecule 1] to be formed.