5.1.2 - homeostasis

• define homeostasis 


  process by which an organism maintains a stable internal environment despite changes in external conditions
• what factors is homeostasis essential for?

  • temperature
  • pH
  • blood glucose levels
• Why is homeostasis important for survival?

  because it allows the body to function efficiently -keeping the body's system in balance and ensuring cell function
• how does maintaining a constant body temperature allow metabolic reactions in cells to provide with maximum efficiency?

  • the highest rate of enzyme activity happens at their optimum temperature (at 37c)
  • If the body temperature is too high, enzymes may become denatured. the enzyme molecules vibrate too much, breaking the hydrogen bonds that hold their 3D shape.
  • The shape of the active site changes, no more substrate can bind so no more ESCs can form
  • (this means that metabolic reactions are less effective - reaction s slow so reduces the KE of molecules)
• define negative feedback

  • the mechanism that reverses a change, bringing the system back to optimum
• how do negative feedback maintain homeostasis?

  1. Detection of a change (stimulus) : receptors detect stimulus and send the input to the coordination centre(CC).
  2. the CC sends an output to the effectors and effectors respond to this output.
  3. effector reacts to reverse the change: closer to optimum stimulus reduced
  4. receptors detect the decrease in stimulus and reduce the input to the CC
  5. effectors reduce their activity and as system gets closer to optimum; response is reduced
• how is temperature controlled by negative feedback for a TEMPERATURE DROP?

  temperature drops -> detected by thermoreceptors in hypothalamus -> effectors > response generated to bring temperature back up

  A)

  B)

  C)

  D)

  E)

  F)

  G)
• how is temperature controlled by negative feedback for a TEMPERATURE INCREASE?

  temperature rises -> detected by thermoreceptors in hypothalamus -> hypothalamus then signals effectors such as sweat glands to cool the body and vasodilation occurs -> there is an increase in blood flow to the skin (reduces body temperature), restoring homeostasis

  
• give examples of where negative feedback occurs

  • body temp
  • blood glucose
  • water balance
• processes of negative feedback to occur:

  • change to internal environment must be detected
  • change signalled to other cells
  • must be an effective response that reverses the changes in conditions
• define positive feedback

  the mechanism that increases a change, taking the system further away from the optimum -> this destabilises the system and is harmful
• how does positive feedback occur?

  • temp drops -> exergonic (biochemical reaction that releases energy) reactions slowed down due to less enzyme activity -> less heat released so temp reduces more
• what is an example of positive feedback loop in the human body?

  • LABOUR
  • blood clotting
  • fever
• how is labour an example of positive feedback in the body?

  • labour at the end of the pregnancy to bring about dilation of the cervix.
  • as the cervix begins to stretch this causes the posterior pituitary gland to secrete the hormone Oxytocin
  • Oxytocin increases the contractions which stretch the cervix more, which causes the secretion of more oxytocin
  • once the cervix is fully dilated, baby can be born and the birth ends the production of oxytocin