One stereotyped view of women portrays us all as creatures at
the mercy of our hormones. 'Balls (or should it be ovaries?) to that!' I say.
Our hormones undoubtedly have a huge influence on our lives, but
there's no reason why we have to become slaves to them.
The more we understand how hormones can affect the female body,
mind and emotions – the better able we will be to minimise their negative
effects and enhance their positive ones.
Infancy
Although we tend to think of hormones kicking in at puberty,
they affect our bodies even during early childhood.
Newborn babies (boys as well as girls) may have enlargement of
one or both breasts, sometimes accompanied by a little milk production.
It has long been thought that this breast development in
newborns is due to female hormones (oestrogens) in the mother's body passing
through the placenta during pregnancy and stimulating breast development in the
baby.
Another suggestion is that the falling level of the mother's
oestrogens in the baby's bloodstream cause the baby’s brain to produce a
hormone called prolactin which can produce some degree of breast enlargement.
This usually disappears after a few weeks, but it may persist
for longer if the breast tissue is stimulated, for example by squeezing the
breast to try to express the milky discharge.
In baby girls mild breast enlargement may reappear sometime in
the first two years, this time due to the child's own hormones affecting breast
tissue.
This breast enlargement may wax and wane repeatedly over months
or even years, before finally disappearing during childhood.
Puberty
At
puberty, hormones
will begin to make major, lasting changes to a girl's body.
Her breasts will get bigger and take on the shape of an adult
woman's
breasts. She will
develop underarm and pubic hair and will get noticeably taller as a significant
growth spurt occurs.
Eventually her
periods will start,
usually as the growth spurt is beginning to slow down. From beginning to end,
the process of puberty usually takes at least four years. Not surprisingly,
some girls experience difficulties adapting to their changing body, emerging
sexuality, the onset of fertility and a degree of emotional turbulence, as they
pass from childhood through adolescence.
All the machinery necessary for going through puberty is present
at
birth, but the body
keeps it switched off for many years.
Eventually, the mechanism that prevents puberty winds down, and
hormones that previously have been held in check can begin to exert their
influence on the body.
A part of the brain called the hypothalamus starts to release
increasingly large and frequent pulses of a hormone called
gonadotrophin-releasing hormone (GnRH).
This stimulates the pituitary gland (also in the brain) to
produce luteinising hormone (LH) and follicle-stimulating hormone (FSH), which
in turn cause a girl's ovaries to start producing other hormones.
Female sex hormones
The most important hormones made by the ovaries are known as
female sex hormones (sex steroids) – and the two main ones are oestrogen and
progesterone. The ovaries also produce some of the male hormone, testosterone.
During puberty, oestrogen stimulates breast development and
causes the vagina, uterus (womb) and Fallopian tubes (that carry eggs to the
womb) to mature.
It also plays a role in the growth spurt and alters the
distribution of fat on a girl's body, typically resulting in more being
deposited around the hips, buttocks and thighs. Testosterone helps to promote
muscle and bone growth.
From puberty onwards, LH, FSH, oestrogen and progesterone all
play a vital part in regulating a woman's
menstrual cycle,
which results in her periods.
Each individual hormone follows its own pattern, rising and
falling at different points in the cycle, but together they produce a
predictable chain of events.
One egg (out of several hundred thousands in each ovary) becomes
'ripe' (mature) and is released from the ovary to begin its journey down the
Fallopian tube and into the womb.
If that egg isn't fertilised, the levels of oestrogen and
progesterone produced by the ovary begin to fall. Without the supporting action
of these hormones, the lining of the womb, which is full of blood, is shed,
resulting in a period.
Pregnancy
If the egg released from the ovary is fertilised and a
pregnancy results, a
woman's hormones change dramatically.The usual fall in oestrogen and progesterone at the end of the
menstrual cycle doesn't occur, so no period is seen.A new hormone, HCG (human chorionic gonadotrophin), produced by
the developing placenta, stimulates the ovaries to produce the higher levels of
oestrogen and progesterone that are needed to sustain a pregnancy.
Most pregnancy testing kits are designed to detect HCG in a
woman's urine, and many can pick up even small amounts just a day or so after
her first missed period.
By the fourth month of pregnancy, the placenta takes over from
the ovaries as the main producer of oestrogen and progesterone. These hormones
cause the lining of the womb to thicken, increase the volume of blood
circulating (in particular the supply to the womb and breasts), and relax the
muscles of the womb sufficiently to make room for the growing baby.
Progesterone and another hormone, relaxin, encourage relaxation
of ligaments and muscles. Greater joint mobility in the pelvic girdle may
increase the capacity of the pelvis in readiness for the baby to pass through
it during childbirth.
Around the time of delivery, other hormones come into play that
help the womb to contract during and after labour, as well as stimulate the
production and release of breast milk.
After childbirth
After
childbirth, what
then?
Levels of oestrogen, progesterone and other hormones fall
sharply, causing a number of physical changes.
The womb shrinks back to its non-pregnant size,
pelvic floor muscle
tone improves and the volume of blood circulating round the body returns to
normal.
The dramatic changes in hormone levels might also play a part in
causing
postnatal depression,
although no real differences have been found in the hormone changes of women
who do, and do not, get postnatal depression. It may be that some women are
more easily affected by these hormonal fluctuations than others.
Talking of hormonal fluctuations, although they have been the
subject of study for many years, we still don't know whether they are
responsible for the wide range of physical and psychological symptoms we now
call
pre-menstrual syndrome or PMS.
No-one doubts that many women experience tender breasts,
abdominal bloating, irritability, low mood and other symptoms in the lead up to
a period but whether these are due to hormone fluctuations, changes in brain
chemicals, social and emotional problems or a combination of all three is a
matter of debate.
The menopause
The next significant hormonal change for most women occurs
around the time of the last period.A woman is said to have reached the
menopause when she
has not had a period for one year.In the UK, the average age for a woman to reach the menopause is
52. If the menopause occurs under 40 years of age, it's known as premature
menopause.It's estimated that premature menopause affects 1 per cent of
women under the age of 40 and 0.1 per cent of women under the age of
30.Over five to ten years leading up to a woman's last period, the
normal functioning of her ovaries begins to deteriorate. This can cause her
menstrual cycle to become shorter or longer, and sometimes it becomes quite
erratic. Periods may become heavier or lighter.Eventually, the ovaries produce so little oestrogen that the
lining of the womb fails to thicken up and so periods stop altogether.Although it's rare for a woman to become pregnant after the
menopause it can, and does, happen so the usual advice is to carry on using
contraception for two
years after your last period if you are under 50 and for one year if you are
over 50.For most of a woman's life, oestrogen helps to protect the heart
and bones, as well as maintaining the breasts, womb, vagina and bladder in
their healthy state.The marked loss of oestrogen in a woman's body that occurs
around, and after, the menopause can, therefore, have detrimental effects on
her health; as well as causing uncomfortable symptoms, such as hot flushes and
night sweats, lack of oestrogen can increase the risk of heart disease and the
bone disorder
osteoporosis.
Other problems include vaginal dryness,
discomfort during
sex, recurrent
urine infections and
incontinence?
It may also contribute to the
depression,
irritability and poor concentration which some menopausal women experience.
But the menopause doesn't have to be a disastrous time for women
– if reduced hormone levels do cause unpleasant symptoms, treatments such as
hormone replacement therapy
(HRT) are often very effective.
HRT and other types of medication can also be used to prevent
health problems, for example if a woman has a significantly increased risk of
developing osteoporosis in the future.
So, from the cradle to the grave, hormones play an important
role in every woman's life. They shape our bodies (quite literally) as well as
some of the most important events we experience, from pregnancy and childbirth
to the menopause.
There may be times when you curse your body's hormones, but
console yourself with the thought that life without them would be much less
interesting!
References
The 5-Minute Pediatric Consult, Schwartz MW et al, Lippincott Williams & Wilkins, 2008The Reproductive System at a Glance, Heffner L, Schust D. Wiley-Blackwell 2010
MacLennan AH. The role of the hormone relaxin in human reproduction and pelvic girdle relaxation, MacLennan AH, Scand J Rheumatol Suppl. 1991; 88:7-15
Written by Gillian Rice, GP
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