Negative feedback

• Where is adrenaline released from?

  Adrenal glands located on top of the kidneys
• What is the primary function of adrenaline in the body?

  To increase heart rate and prepare the body for 'fight or flight'
• What are the effects of adrenaline on the body?

  • Causes glycogen to be broken down into glucose
  • Increases the diameter of small arteries in the muscles
  • Increases heart rate
  • Increases blood pressure
  • Increases breathing rate
  • Decreases the diameter of small arteries in the skin and gut
• Why is an increase in heart rate important during stress?

  It pumps more blood carrying oxygen and glucose to the brain and muscles
• Where is thyroxine produced?

  Thyroid gland
• What are the effects of thyroxine on the body?

  Regulates basic metabolism, stimulates protein synthesis, growth, and development
• What hormone stimulates the release of thyroxine?

  Thyroid stimulating hormone (TSH)
• Describe the negative feedback mechanism for thyroxine levels.

  • If thyroxine levels are too high:
  • TSH secretion from the pituitary gland stops
  • Thyroxine release from the thyroid gland reduces
  • Levels return to normal
  • If thyroxine levels are too low:
  • TSH secretion from the pituitary gland starts again
  • Thyroxine release from the thyroid gland increases
  • Levels return to normal
• How does negative feedback function in the regulation of thyroxine levels?

  It triggers responses to bring levels back to normal when they are too high or too low
• What condition results from high thyroxine levels?

  Hyperthyroidism
• What condition results from low thyroxine levels?

  Hypothyroidism
• What happens to TSH secretion when thyroxine levels are high?

  TSH secretion from the pituitary gland is inhibited
• What happens to TSH secretion when thyroxine levels are low?

  TSH secretion from the pituitary gland is stimulated
• How can you visualize the negative feedback system for thyroxine levels?

  • Think of it like a thermostat:
  • If it gets too hot (high thyroxine), it switches off (inhibits TSH)
  • If it gets too cold (low thyroxine), it switches back on (stimulates TSH)