Animal Hormones (Edexcel GCSE Biology)
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- FrontThe Endocrine System
What is the endocrine system?
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What is the endocrine system?
The endocrine system is composed of glands that secrete hormones directly into the bloodstream.
How are hormones transported around the body?
Hormones are carried around the body in the blood.
Identify the glands labelled A, B and C.
The glands are:
A = pancreas
B = adrenal gland
C = testes
What is the function of the pituitary gland?
The pituitary gland is a 'master gland' that secretes several hormones into the blood in response to body conditions. These hormones act on other glands to stimulate the release of additional hormones.
Which hormones are released by the ovaries?
The ovaries produce the female sex hormones oestrogen and progesterone.
Which gland produces the hormone insulin?
Insulin is produced by the pancreas.
What are the main glands of the endocrine system?
The main glands of the endocrine system include the:
pituitary gland
thyroid gland
pancreas
adrenal
ovaries
testes
Where is adrenaline produced? (Higher Tier Only)
Adrenaline is produced by the adrenal glands located on top of the kidneys.
What is the role of the hormone adrenaline? (Higher Tier Only)
The hormone adrenaline prepares the body for fight or flight.
What are the effects of adrenaline on the body? (Higher Tier Only)
The effects of adrenaline on the body include:
increased heart rate
increased blood pressure
increased blood flow to the muscles
stimulating the liver to change glycogen into glucose, which is then released into the blood
Why does increased blood flow to the muscles help the body prepare for fight or flight? (Higher Tier Only)
Increased blood flow to the muscles helps the body prepare for fight or flight as greater amounts of glucose and oxygen can be delivered to the cells for aerobic respiration, which releases energy.
True or False?
The liver is stimulated by adrenaline to change glucose into glycogen. (Higher Tier Only)
False.
The liver is stimulated by adrenaline to change glycogen into glucose.
This raises blood sugar levels for increased respiration and therefore energy release.
What is the role of the hormone thyroxine? (Higher Tier Only)
Thyroxine controls metabolic rate, e.g. the rate at which carbohydrates are broken down inside cells.
Define the term negative feedback. (Higher Tier Only)
Negative feedback describes a control mechanism that functions to reverse any change in conditions to return to the set point.
Which gland secretes thyroxine? (Higher Tier Only)
Thyroxine is secreted by the thyroid gland in the neck.
What happens if the level of thyroxine falls below normal levels? (Higher Tier Only)
If the level of thyroxine falls below normal levels:
TRH is released by the hypothalamus
this increases the release of TSH from the pituitary gland
TSH stimulates the thyroid to release more thyroxine
What happens if the level of thyroxine is too high? (Higher Tier Only)
If the level of thyroxine is too high:
TRH production is inhibited
the release of TSH from the pituitary is therefore also inhibited
less thyroxine is released from the thyroid gland
What is the menstrual cycle?
The menstrual cycle is the sequence of events that includes the thickening of the uterus lining, ovulation and menstruation; it is controlled by a series of hormones.
Describe the stages of the menstrual cycle.
The stages of the menstrual cycle include:
days 1-7: the loss of the uterus lining during menstruation
days 8-14: thickening of the uterus lining
day 14: release of an egg cell during ovulation
days 14-28: continued thickening and maintenance of the uterus lining
The days are approximate and will vary between individuals.
What is the role of oestrogen in the menstrual cycle?
Oestrogen is required to stimulate the thickening of the uterus lining.
True or False?
An increase in progesterone results in the loss of the uterus lining.
False.
A decrease in progesterone levels at the end of the cycle results in the loss of the lining during menstruation.
What is the role of FSH in the menstrual cycle? (Higher Tier Only)
FSH is released by the pituitary gland and causes an egg to start maturing in the ovary.
What happens to oestrogen levels during the menstrual cycle? (Higher Tier Only)
Oestrogen levels rise from day 1 and peak just before day 14. The peak in oestrogen occurs just before the egg cell is released.
True or False?
Oestrogen inhibits release of the hormone FSH. (Higher Tier Only)
True.
Rising oestrogen levels during the first half of the menstrual cycle inhibit the release of FSH from the pituitary gland..
Which hormone is released by the pituitary gland to stimulate ovulation? (Higher Tier Only)
The pituitary gland releases LH to trigger ovulation (the release of an egg).
What causes the peak in LH seen at day 14? (Higher Tier Only)
The peak in LH occurs as a result of rising oestrogen levels.
What happens to progesterone levels during the menstrual cycle? (Higher Tier Only)
Progesterone levels are low from day 1 – 14 and starts to rise once ovulation has occurred. Levels then decrease towards the end of the cycle.
How do hormonal contraceptives prevent pregnancy?
Hormonal contraceptives prevent pregnancy because they prevent the release of a mature egg cell during the menstrual cycle.
True or False?
Hormonal contraceptives prevent the maturation of a follicle by inhibiting the release of oestrogen.
False.
Oestrogen is not the hormone responsible for the maturation of the egg. Hormonal contraceptives that inhibit FSH production will ensure that no egg cells mature.
What is an example of a barrier method of contraception?
Barrier methods of contraception include:
condoms
diaphragms
Why might it sometimes be recommended to use barrier methods of contraception over hormonal options?
Barrier methods of contraception might be recommended as:
they provide protection against sexually transmitted diseases
the side effects associated with hormonal birth control can be avoided
Define the term infertility. (Higher Tier Only)
Infertility refers to the difficulty or inability of a couple to conceive naturally.
What are assisted reproductive technologies (ART)? (Higher Tier Only)
ART is technology that increases the chances of pregnancy.
How does clomifene therapy work as an ART? (Higher Tier Only)
Clomifene is a drug given to women which causes more FSH and LH to be released. This stimulates egg maturation and ovulation.
True or False?
IVF allows egg cells to be fertilised inside the body. (Higher Tier Only)
False.
IVF allows egg cells to be fertilised outside the body.
What are the main steps of IVF treatment? (Higher Tier Only)
The main stages of IVF are as follows:
mature egg cells are collected from the mother
egg cells are fertilised by sperm from the father in the laboratory
the fertilised eggs develop into embryos
one or two embryos are inserted into the mother's uterus