Features of Homeostasis

• Homeostasis - Maintenance of a stable and constant internal environment within strict limits
• Homeostasis is the ability to respond to changing factors (pH etc) and return the system to an optimum point
• Organisms that can control their own internal environment are more independent of their environment:

  • Greater geographical range so can colonise more habitats and ecosystem
  • Greater chance of finding food, shelter or mates
• Features of homeostasis:

  • The optimum level
  • A receptor that detects a deviation from this optimum level
  • Controller (brain) that coordinates a response
  • Effector which brings about the changes needed
  • Feedback loop (receptor informed of effectors actions)
• Negative feedback - Increase or decrease from the optimum point so the opposite effect is instigated (this response returns the point to the optimum point)
• Positive feedback - When a deviation from an optimum point causes an even greater deviation from the normal
• Example of positive feedback - contractions:

  • Baby pushes against the cervix and so it is stretched
  • Stretching of cervix causes nerve impulses to be sent to the brain
  • Brain stimulates release of oxytocin
  • Oxytocin causes uterus to contract
  • This causes the baby to push against cervix and so the cycle continues
• Thermoregulation is the regulation of body temperature
• Thermoregulation:

  • If body temperature is too low enzyme reactions are too slow
  • If the body temperature is too high enzymes could denature
  • If blood pH deviates from the normal then proteins may denature
• Endotherms (mammals, bird, some fish etc) maintain body temperature by both physiological and behavioural means
• Ectotherms (reptiles, amphibians, fishes etc) maintain body temperature by behavioural means only e.g. exposing themselves to the sun, taking shelter, gaining warmth from the ground