Negative Feedback

• Adrenaline is produced in times of stress, and stimulates the fight or flight response

  • Released by the adrenal glands (on top of the kidneys)
  • This is stimulated by fear or stress, detected in the brain
  • The effects of adrenaline increases heart rate and breathing rate to deliver more oxygen and glucose to the brain and muscles for aerobic respiration

  
• Thyroxine stimulates metabolic rate (how quickly reactions occur). It's also important in growth and development/

  • Released by the thyroid gland
  • Its release is stimulated by the thyroid stimulating hormone
  • The level of thyroxine in the blood is controlled by negative feedback

  
• • The level of thyroxine in the blood is monitored by the brain
  • When thyroxine levels falls, the pituitary gland releases TSH into the bloodstream
  • TSH triggers the thyroid gland to release more thyroxine into the blood
  • The increased level of thyroxine is detected by the brain which prevents the pituitary gland from releasing TSH
  • As TSH level falls, the thyroid gland releases less thyroxine
  • Low thyroxine levels trigger events to increase it. High thyroxine levels trigger events to decrease it - this is called a negative feedback cycle