Homeostasis

• What is homeostasis?

  Homeostasis is the body's ability to maintain a stable/constant internal environment despite external changes.
• Important factors to keep constant in the body:

  1. Temperature - affects enzyme activity, diffusion, osmosis etc
  2. Glucose - important for respiratory substrates, for growth and repair, affects water potential
  3. CO2/pH - CO2 lowers pH, affecting enzyme action
  4. Water potential - dehydration, thickening of blood, increased blood pressure, affects water potential
• Positive feedback:

  When a change is detected, it is then amplified - the system reverts back to normal when the stimulus is removed

  E.g. during the formation of a blood clot, platelets become activated and release a chemical which triggers more platelets to become activated - the platelets then quickly form a blood clot
• Negative feedback:

  When a factor falls outside its preset range, mechanisms are activated to bring it back within that range

  Homeostasis systems involve receptors, a communication system, and effectors. Receptors detect a change, and this is communicated via the nervous/hormonal system. The effectors respond to counteract the change
• Thermoregulation:

  Temperature is controlled by the hypothalamus - if blood temp is too high, this triggers nervous impulses in the autonomic nervous system, which switches on cooling mechanisms and vice versa

  When temperature is too high:

  Detected by thermoreceptors in hypothalamus and skin - causes vasodilation/hair lies flat and sweating - temperature decreases back to optimum

  When temperature is too low:

  Detected by thermoreceptors in hypothalamus and skin - causes vasoconstriction/hair is erect/shivering - temperature increases back to optimum
• What is glucoregulation?

  The control of blood glucose concentration. A constant supply of glucose is needed for cell respiration/ very high levels of glucose raises the solute potential of the blood, drawing extra fluid in which dehydrates and damages cells