the role of negative feedback 5.3.7

• the main principles of negative feedback are:

  • to maintain a steady state
  • if a factor in the internal environment increases, changes take place to decrease it and restore the original level
  • if a factor in the internal environment decreases, changes take place to increase it and restore the original level
  • whatever the initial change, in negative feedback the response causes the oppposite
• examples of negative feedback include:

  • control of body temperature
  • control of water content of blood
  • control of thyroxine levels
  • control of blood glucose
• the thyroid gland is found in your neck
• the thyroid gland uses iodine from the diet to make thyroxine
• thyroxine:

  • controls the basal metabolic rate of your body
  • ie how quickly substances are broken down and built up
  • how much oxygen your tissues use
  • how the brain of a growing child develops
• TSH is thyroid stimulating hormone
• if thyroxine levels rise, TSH levels fall- so thyroxine levels return to normal
• if thyroxine levels fall, TSH levels rise, so thyroxine levels return to normal
• thyroxine levels are controlled by negative feedback
• adrenaline is made in the adrenal gland
• adrenaline is released when you are stressed, angry or happy
• heart rate and breathing rate increase to help the body prepare for action because more oxygen is transferred to the blood, to allow an increased rate of aerobic respiration. it also removes carbon dioxide that is produced faster
• adrenaline causes stored oxygen in the liver to be converted into glucose which helps the body prepare for action as there is more glucose in the blood to allow for an increased rate of respiration@
• adrenaline causes the pupil of the eye to dilate which helps the body prepare for action because it lets more light into each eye to improve the perception of danger
• adrenaline causes a mental awareness increase which helps the body prepare for danger because there is a better perception of threats
• adrenaline causes blood to be diverted away from the digestive system which helps the body prepare for action because it allows the blood to be diverted to the muscles and brain instead
• adrenaline causes blood to be diverted to the skeletal muscles which helps the body prepare for action because more blood (carrying oxygen and glucose) is delivered to muscles - so more respiration for harder muscle contractions
• adrenaline causes blood to be diverted to the brain which helps the body prepare for action because more blood carrying oxygen and glucose is delivered to the brain to allow increased mental awareness
• if the danger passes, the adrenaline stops being released
• adrenaline is not controlled by negative feedback because there is no system to keep adrenaline to an optimum level and it is only released when needed