negative feedback

• Many hormones in your body are controlled as part of negative feedback systems.
• Negative feedback systems work to maintain a steady state.
• If a factor in the internal environment increases, changes take place to reduce it and restore the original level.
• Whatever the initial change, in negative feedback the response causes the opposite
• If a factor in the internal environment decreases, changes take place to increase it and restore the original level.
• Many hormones are involved in negative feedback systems, including insulin and glucagon, most female sex hormones, and thyroxine.
• The thyroid gland in your neck produces the hormone thyroxine. 

  Thyroxine controls: 

  • the basal metabolic rate of your body; how quickly substances are broken down and built up
  • How much oxygen your tissues use
  • How the brain of a growing child develops
• Thyroxine plays an important part in growth and development.
• Thyroxine levels are kept stable by negative feedback involving the pituitary gland and the hormone it produces - thyroid stimulating hormone or TSH.
• • If levels of thyroxine in the blood begin to fall, it is detected by sensors in the brain. 
  • As a result, the amount of TSH released from the pituitary gland increases. 
  • TSH stimulates the production of thyroxine by the thyroid gland. 
  • As the level of thyroxine goes up, it is detected by the sensors and in turn the level of TSH released falls
• If you are stressed, angry, excited, or frightened your body needs to be ready for action. Your adrenal glands, located at the top of your kidneys, secrete adrenaline that is carried rapidly around the body in your blood.
• Adrenaline causes:

  • your heart rate and breathing rate to increasestored glycogen in the liver to be converted to glucose for respiration the pupils of your eyes to dilate to let in more light
  • your mental awareness to increase
  • blood to be diverted away from your digestive system to the big muscles of the limbs.
• • Adrenaline boosts the delivery of oxygen and glucose to your brain and muscles, preparing your body for flight or fight. 
  • Once the danger is over, the adrenal glands stop releasing adrenaline and your systems return to their resting levels. 
  • This does not involve a negative feedback loop.