9.1-9.2 homeostasis + mammal control

• what is homeostasis?

  • stable internal environment
  • maintained by state of dynamic equilibrium
  • in the body
• why does core body temperature need to remain stable?

  • changes in temperature affect enzyme activity....
  • temperature too high = enzymes denature
  • temperature too low = insufficient kinetic energy
• why does blood pH need to remain stable?

  • changes in pH can affect enzyme activity
  • too acidic = H+ ions interact with hydrogen bonding in tertiary structure. changes active site shape. no longer complimentary
• why does blood water potential need to be stable?

  • changes in water potential cause cell lysis or shrinkage
  • can disrupt hydrolytic reactions.
• negative feedback

  • returns internal environment to optimum when it fluctuates
• steps of negative feedback

  • stimulus (change) in internal environment
  • detected by receptors
  • receptors activate the mechanism to reverse the change
  • conditions return to normal - mechanism switched off
• positive feedback

  • fluctuation triggers change
  • resulting in levels higher than normal
• steps of positive feedback?

  • stimulus in internal environment
  • detected by receptors
  • receptors activate mechanism to continue change
• hormones

  • chemicals secreted by endocrine glands
  • transported around blood
  • specific tertiary structure - complimentary to surface receptor proteins
• 2 types of hormones

  • peptide hormones - bind to receptor on surface, stimulating secondary messenger
  • steroid hormones - form hormone-receptor complex and act as transcription factor
• mode of action for peptide hormones - link to adrenaline

  • hormone attaches to receptor protein on target cell
  • activating G protein enzyme on the inside of the membrane
  • G protein hydrolyses ATP to cyclic AMP (cAMP)
  • cAMP activates cascade of reactions to bring about right response.
  • such as protein kinase A for adrenaline
• mode of action for steroid hormone - linked to oestrogen

  • oestrogen diffuses through membrane and into cell nucleus
  • bind to receptor which is held in a protein complex
  • causes oestrogen receptor to change shape and leave complex
  • inhibits action
  • activated oestrogen receptor binds to promoter region
  • acts as transcription factor
• why is there a time lag between hormone production and response?

  • time taken to produce hormone
  • transport in blood
  • cause change to the target protein