Hormones 1 - Revision

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  • Animal Coordination, Control and Homeostasis
    • Hormones
      • Chemical messengers released in the bloodstream
      • They only affect target organs
      • Endocrine glands
        • Pituitary gland
          • Produces many hormones that regulate body conditions
        • Thyroid gland
          • Produces thyroxine- Regulates the rate of metabolism, heart rate and temperature
        • Adrenal glands
          • Produces adrenaline- Needed to prepare the body for a 'fight or flight' response
        • Testes
          • Produces testosterone- Controls puberty and sperm production in males
        • Pancreas
          • Produces insulin- Used to regukate the blood glucose level
        • Ovaries
          • Produces  oestrogen- Involved in the menstrual cycle
      • Hormone and Neurons
        • Neurones- Very fast action +  Act for a very short time + Acts on a precise area
        • Hormones- Slower action +  Acts for a long time + Acts in a general way
      • Produced by the endocrine glands which make up your endocrine system
    • Adrenaline and Thyroxine
      • Adrenaline prepare you for 'fight or flight'
        • 1 Released by the adrenal glands (just above the kidneys)
      • Negative Feedback
        • Ensures that, in any control system, changes are reversed and returned back to the set level
          • eg. negative feedback keeps our body temperature at a constant 37°C. If we get too hot, blood vessels in our skin vasodilate (become larger) and we lose heat and cool down
            • If we get too cold blood vessels in our skin vasoconstrict (become smaller), we lose less heat and our body warms up
      • Thyroxine regulates metabolism
        • 1 Released by the thyroid gland
        • 2 It plays an important part in regulating metabolic rate- the speed at which chemical reactions in the body occur
        • 3 A negative feedback system keeps the amount of thyroxine in the blood at the right level
          • * When the blood thyroxine level is lower than normal, the hypothalamus (a structure in the brain) is stimulated to release TRH
            • * TRH stimulates the pittuitary gland to release TSH
              • * TSH stimulates the thyroid gland to release thyroxine so the blood thyroxine levels rises back towards normal
                • * When the blood thyroxine level becomes higher than normal, the release of TRH from the hypothalamus is inhibited, which reduces the production of TSH so the blood thyroxine level falls


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