Hormone systems - menstrual cycle
Doc Brown's Biology Revision Notes
Suitable for GCSE/IGCSE/O level Biology/Science courses or equivalent
This page will answer many questions e.g.
What are hormones?
How does the menstrual cycle work?
How does In Vitro Fertilisation'
How can hormones be used to control fertility?
What are FSH and LH hormones and what do they
You should appreciate that the nervous system and hormones enable us to respond to external changes.
The nervous system and hormones also help us to control
conditions inside our bodies.
Know that hormones are used in some forms of contraception
and in fertility treatments.
Know and understand that many
process within the
body are coordinated and controlled by chemical substances called hormones.
Know that hormones are
secreted by glands and are usually transported to their target organs by the
Hormones, being directly
released into the blood, are quite rapidly carried to all parts of the body
BUT only affect the function of particular cells.
The activated cells are called
'target cells' and have a chemical receptor that responds to the hormone.
They are effectively act as
'chemical messages' to trigger particular biochemical reactions and their
effect is relatively long-lasting compared to eg the nervous impulses and
responses of reflex arc.
The pituitary gland produces the
hormones FSH and LH which are important control chemicals in the female
The Menstrual Cycle
Stage 1 - the bleeding starts on
day 1 as the uterus lining breaks down for 4 days.
Stage 2 - over 5 to 14 days the
uterus builds up again to give a thickish layer of tissue to receive a
Stage 3 - about day 14 an egg is
released from the ovary
Stage 4 - the thickened uterus
tissue lasts for around 14 days and if no fertilised egg is received the
uterus lining breaks up and the cycle repeats itself.
The ovaries produces the hormone
oestrogen, which is also involved in the menstrual cycle.
c) Know and understand that hormones regulate the
functions of many organs and cells.
d) Know and understand that several hormones are involved
in the menstrual cycle of a woman and hormones are involved in promoting the
release of an egg:
The follicle stimulating hormone (FSH)
is secreted by the pituitary gland and causes eggs to mature in the ovaries
and it also stimulates the ovaries to produce hormones including oestrogen,
The luteinising hormone (LH,
also from the pituitary gland) stimulates the release
of eggs from the ovary.
The hormone oestrogen is secreted by the ovaries,
causes the formation of LH in the pituitary gland and inhibits
the further production of FSH.
e) Know and understand about the uses of hormones in controlling fertility including:
giving oral contraceptives that contain hormones
to inhibit FSH production so that no eggs mature, noting that ...
Oral contraceptives eg 'the
pill' may contain oestrogen and
progesterone to inhibit egg maturation ie prevent egg release, high and
sustained levels of oestrogen inhibit FSH production and egg development is
stopped permanently as long as the contraceptive is taken.
However, the first birth-control pills contained
too large amounts
of oestrogen which resulted in some women suffering
significant side effects eg headaches, nausea, irregular bleeding, fluid
retention and blood clots.
Birth-control pills now contain a much lower dose
of oestrogen, or only contain another hormone called progesterone.
Progesterone-only pills lead to fewer side effects
but is not quite as effective as oestrogen pills.
giving FSH and LH in a ‘fertility drug’ to a woman
whose own level of FSH is too low to stimulate
eggs to mature, for example in 'In Vitro Fertilisation'
(IVF) treatment noting that ..
... IVF involves giving a mother FSH and LH to
stimulate the maturation of several eggs where they would not have been released.
IVF has enabled many mothers to
get pregnant and give birth to healthy children, but it doesn't always work
for an infertile couple.
Also, its possible for several
eggs to be simultaneously matured resulting in multiple pregnancies eg
twins, triplets and more!
Women can suffer side-effects
from the hormone treatment which can be physically and emotionally
demanding, but most infertile couples would regard IVF treatment is worth
In IVF treatment, after the
potential mother has been treated with FSH and LH, eggs are collected from
her ovaries and
fertilised in the laboratory by sperm from the father.
eggs grow and develop into embryos.
At the stage when
they are tiny balls of cells, one or two embryos
are inserted into the mother’s uterus (womb) to attempt a pregnancy.
Note that knowledge of the role of progesterone in
the natural menstrual cycle, including details of negative feedback, is NOT
You are expected to use
appropriate skills, knowledge
and understanding to:
evaluate the benefits of, and the problems that may
arise from, the use of hormones to control fertility,
including In Vitro Fertilisation (IVF)
- you will be given information data to work on,
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