Hormonal Coordination


Principle of Hormonal Control

- the endocrine system is composed of glands that secrete chemicals called hormones directly into the blood stream, the blood carries the hormone to a target organ where it produces an effect, compared to the nervous system, the effects of hormones are often slower but longer lasting

    pituitary: controls growth in children, stimulates thyroid gland to control rate of metabolism, stimulates ovaries to produce and release eggs to make oestrogen, stimulates the testes to make sperm and testosterone

    thyroid: controls the metabolic rate of body

    pancreas: controls levels of glucose in the blood

    adrenal: prepares the body for stressful situations- 'fight or flight' response

    ovaries: development of secondary sexual characteristics and involved in menstrual cycle

    testes: development of secondary sexual characteristics, involved in production of sperm

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Control of Blood Glucose Levels

- your blood glucose concentration is monitored and controlled by your pancreas

- pancreas produces the hormone insulin, allows glucose to move from the blood into the cells and to be stored as glycogen in the liver and muscles

- pancreas also produces glucagon, allows glycogen to be converted back into glucose and released into blood

- glucagen interacts with insulin in a negative feedback cycle to control glucose levels

- type 1 diabetes, the blood glucose may rise to fatally high levels because the pancreas does not secrete enough insulin

- type 2 diabetes, the body stops responding to its own insulin

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Treating Diabetes

- type 2 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 excercise, if this doesn't work, drugs may be needed

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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 times of fear or stress, it increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for 'fight or flight'

- thyroxine is controlled by negative feedback whereas adrenaline is not

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Human Reproduction

- during puberty reproductive hormones cause secondry sexual characteristics to develop

- oestrogen is the main female reproductive hormone produced by the ovary, 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 hormone (LH), oestrogen, and progesterone

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Hormones and Menstrual Cycle

- interactions of 4 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 ihibits 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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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 and patches

- barrier methods such as condoms and diaphragms, intrauterine devices, spermicidal agents, abstinence and surgical sterilisation

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Infertility Treatments

- FSH and LH can be used as a fertility drug to stimulate ovulation in women with low FSH levels

- in vitro fertilisation (IVF) uses FSH and LH to stimulate maturation of ova that are collected, fertilised, allowed to start development and replaced in the uterus

- IVF is emotionally and physically stressful, often unsuccessful and can lead to risky multiple births

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Plant Hormones and Responses

- plants are sensitive to light and gravity

- plant responses to light and gravity are brought about by the plant hormone auxin

- the responses of roots and shoots to stimuli of light and gravity are the result of the unequal distribution of auxin

- shoots grow towards light and against the force of gravity

- roots grow in the direction of the force of gravity

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Using Plant Hormones

- plant hormones are used in agriculture and horticulture

- auxins are used as weed killers, rooting powders and in tissue culture

- ethene is used to control fruit ripening

- gibberellins can be used to increase fruit size, end seed dormancy and promote flowering in the malting process, and increase the yield of sugar cane

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