Negative Feedback

• If the levels of thyroxine in the blood falls, TSH levels rise and vice versa.
• Adrenaline is secreted by the adrenal glands
• Adrenaline release causes:

  • Heart + breathing rate to increase
  • Stored glycogen in the liver to be converted to glucose for respiration
  • The pupils of your eyes dilate to let in more light
  • Mental awareness increases
  • Blood diverted away from digestive system to the big muscles of your limbs.
• The response to stress is not an example of a negative feedback system as once the danger is over, the adrenal glands stop releasing adrenaline and your systems return to their resting levels.
• If your body temperature falls, then the thermoregulatory centre (hypothalamus) sends impulses which cause:

  • Vasoconstriction (less blood is supplied to capillaries in skin)
  • No sweat
  • Hairs on skin upright
  • Shivering (releases energy in muscles)
• If your body temperature rises, then the thermoregulatory centre (hypothalamus) sends impulses which cause:

  • Vasodilation (more blood supplied to capillaries + skin)
  • Lots of sweat released
  • Hairs on skin lie flat