Negative feedback HT: Homeostasis and response: Biology: GCSE (9:1)

• Negative feedback loop

  Where a change in something brings about a process that causes the opposite effect, keeping levels constant

  
• Positive feedback loop


  A process in which the end products of an action cause more of that action to occur in a feedback loop, for example adrenaline promotion

  
• Thyroxine or thyroid hormone


  A hormone which stimulates the basal metabolic rate and plays an important role in growth and development

  
• Thyroid gland


  Releases thyroxine in response to stimulation by TSH

  
• Thyroid-stimulating hormone (TSH)


  A hormone released by the pituitary gland which stimulates the thyroid gland to release thyroxine

  
• Thyroxine negative feedback


  When thyroxine levels are high, thyroxine inhibits itself by signalling the pituitary gland to stop releasing TSH

  
• Basal metabolic rate


  The rate of activity from basic life-sustaining metabolic processes that occur in the body, even when at rest
• Adrenaline


  A hormone secreted by the adrenal glands that regulates internal conditions required for a fight or flight response

  
• Effects of adrenaline on the body

  Increased heart and ventilation rate, increased blood supply to key organs, promotion of glucagon and inhibition of insulin

  
• Adrenal glands

  Glands situated above the kidneys that are responsible for the release of adrenaline during a fight or flight response

  
• Fight or flight response


  A physiological reaction that occurs in response to a stimulus that is perceived as being stressful

  
• Stress

  Exposure to a negatively perceived stimulus that can be physical or emotional
• Increased heart rate

  Blood is pumped quicker during fight or flight and can reach key structures quickly to provide them with glucose and oxygen

  
• Increased ventilation rate

  Gas exchange can occur quicker during fight or flight so that more oxygen is available for aerobic respiration

  
• Reduced blood supply to the gut


  Reduces the supply of glucose and oxygen to digestive organs, which are not a priority during fight or flight
• Increased blood supply to the brain and muscles

  Provides the brain and muscles with more glucose and oxygen during fight or flight, allowing quicker responses to stressful stimuli

  
• Glucose and oxygen


  Reactants required for aerobic respiration, so that energy can be released and supplied to key organs during fight or flight

  
• Pancreas during fight or flight

  Inhibits insulin and promotes glucagon so that increased levels of glucose are available for respiration

  
• Negative feedback of reproductive hormones

  If the levels of one reproductive hormone are too high, another reproductive hormone such as progesterone will inhibit it
• Negative feedback of insulin and glucagon

  High levels of blood glucose leads to insulin production and low levels of blood glucose leads to glucagon production