B11: Hormonal Coordination


B11.1: Principles of Hormonal Coordination

  • the endocrine system is made up of glands which secrete chemicals called hormones into the bloodstrem. the blood carries the hormone to a target organ where it produces an effect.
  • compared to the nervous system, the effects of hormones are slower but last longer. 
  • the pituitary gland is the master gland and secretes several hormones into the blood in response to body conditions. some of these hormones act on other glands to stimulate them to release hormones to bring specific effects. 
  • the key endocrinal glands:
    • pituitary gland
    • thyroid
    • pancreas
    • adrenal glands
    • ovaries
    • testes
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B11.2: The Control of Blood Glucose Levels

  • the blood glucose concentration is monitered and controlled by the pancreas.
  • the pancreas produces the hormone insulin which allows glucose to move from the blood into the cells to be stored as glycogen in the liver and muscles
  • the pancreas also produces gluacagon which allows glycogen to be converted back into glucose and released into the blood.
  • glucagon interacts with insulin in a negative feedback cycle to control glucose levels.
  • in type 1 diabetes, the blood glucose may rise to fatally high levels because the pancreas does not secrete enough insulin.
  • in type 2 diabetes, the body stops responding to its own insulin. 
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B11.3: Treating Diabetes

  • type 1 diabetes is normally controlled by injecting insulin to replace the hormone that is not made in the body.
  • type 2 diabetes is often treated by a carbohydrate-controlled diet and taking more exercise. if this doesn't work, drugs may be needed.
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B11.4: The Role of Negative Feedback

  • thyroxine from the thyroid gland stimulates the basal metabolic rate.
  • it plays an important role in growth and development.
  • adrenaline is produced by the adrenal glands in time of fear and stress. it increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for flight or fight. 
  • thyroxine is controlled by negative feedback whereas adrenaline is not. 
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B11.5: Human Reproduction

  • during puberty reproductive hormones cause secondary sexual characteristics to develop
  • oestrogen is the main female reproductive hormone produced by the ovaries. at puberty, eggs begin to mature in the ovary and one is released approximately every 28 days at ovulation. 
  • testosterone is the main male reproductive hormone produced by the testes and stimulates sperm production.
  • hormones involved in the menstrual cycle of a woman include follicle stimulating hormone (FSH), luteinising hormore (LH), oestrogen and progesterone. 
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B11.6: Hormones and the Menstrual Cycle

  • the interactions of four hormones control the maturing and release of an egg from the ovary and the build up of the lining of the uterus in the menstrual cycle.
  • FSH from the pituitary stimulates eggs to mature in the follicles of the ovary and the ovary to produce oestrogen.
  • oestrogen secreted by the ovaries stimulates the growth of the lining of the uterus and the release of LH and inhibits FSH.
  • LH stimulates ovulation.
  • progesterone is produced by the empty follicle after ovulation. it maintains the lining of the uterus for around 10 days and inhibits FSH and LH. 
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B11.7: The Artificial Control of Fertility

  • fertility can be controlled by a number of hormonal and non-hormonal methods of contraception.
  • contraceptive methods include:
    • oral contraceptives
    • hormonal injections
    • implants
    • patches
    • barrier methods
    • intrauterine devices
    • spermicides
    • abstinence
    • surgical sterilisation 
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B11.8: Infertility Treatments

  • FSH and LH can be used as a fertility drug to stimulate ovulation in women with low FSH levels. 
  • in vitro fertilisation uses FSH and LH to stimulate maturation of ova that are collected, fertilised, allowed to start development and are implanted into the uterus. 
  • IVF is emotionally and physically stressful, often unsuccessful, expensive and can lead to risky multiple births. 
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