B1.2.2 - Control in the Human Body

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  • B1.2.2 - Control in the Human Body
    • Controlling Internal Conditions
      • Internal conditions that are controlled include:
        • Water leaves the body via the lungs when we breathe out.
        • Ions and water are lost via the skin when we sweat, to cool us down.
        • The excess ions and water are lost via the kidneys in the urine
        • -Temperature, to maintain the temp at which enzymes work best
        • -Blood sugar levels, to provide cells with a constant supply of energy
    • Hormones
      • Many processes within the body are coordinated by chemical substances called hormones
      • They regulate functions of many organs and cells.
        • 1. Hormones are secreted by a gland into the blood
        • .2. Hormones are transported around the body in thebloodstream to their target organs
        • 3. Hormones cause a response from a target organ
    • The Menstrual Cycle
      • Hormones secreted by the pituitary  gland and the ovaries control the thickness of the uterus lining and the release of an egg.
        • Follicle-stimulating hormone  (FSH)
          • Causes eggs in ovaries to mature
          • Stimulates ovaries to produce  oestrogen
          • Secreted by the pituitary gland
        • Lutenising  Hormone (LH)
          • Secreted by the pituitary gland
          • Inhibits production of oestrogen
          • Causes  ovulation
        • Oestrogen
          • Inhibits production of FSH so no more eggs mature that month.
          • Causes uterus lining to thicken in first half of cycles
          • High levels stimulate production of LH
          • Secreted by the ovaries
        • Progesterone
          • Maintains thick uterus lining if egg is fertilised
          • High levels stop the cycle
          • Secreted by the ovaries
    • Controlling Fertility
      • Oral contraceptives
        • Oestrogen  and progesterone to inhibit FSH -> no eggs mature   -> no eggs are released
        • Early contraceptives contained large amounts of oestrogen caused significant side effects
        • Modern pills contain a much lower dose of oestrogen or are progesterone only, which lead to fewer side effects
      • Fertility drugs
        • For women whose levels of FSH are too low to stimulate egg  maturation
        • Fertility drugs contain FSH and LH
      • IVF
        • 2. Eggs collected from ovaries and fertilised by sperm from the father
        • 3. Fertilised eggs develop into embryos
        • 4. When embryos are tiny balls of cells, one or two are inserted into the uterus
        • 1. Mother given fertility drugs to stimulate  maturation of several eggs


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