Physiology of the female reproductive system
The female reproductive system consists of the external and the
internal genitalia. The external genital organs are visible
outside the body and begin to mature when a girl reaches puberty.
The internal genitalia are the organs where fertilisation and
conception takes place. The uterus, fallopian tubes, ovaries and
the vagina are the main structures of the female reproductive
system. The organs of sexual reproduction are the gonads, which
are the ovaries in females and the testes in males. Females
produce female gametes or eggs (males produce male gametes or
sperms). Sexual reproduction is the fertilization of a female
gamete by a male gamete.
When a female is born, each of her ovaries has hundreds of
thousands of eggs, but they remain dormant until her first
menstrual cycle, which occurs during puberty. At this time, during
adolescence, the pituitary gland secretes hormones that stimulate
the ovaries to produce female sex hormones, including oestrogen,
which helps the female develop into a sexually mature woman. Also,
at this time, females begin releasing eggs as part of a monthly
period called the menstrual cycle. Approximately once a month,
during ovulation, an ovary discharges a tiny egg that reaches the
uterus through one of the fallopian tubes. Unless fertilised by a
sperm while in the fallopian tube, the egg dries up and is
expelled from the uterus. If a female and male have sexual
intercourse within four days of ovulation, fertilisation can
occur. When the male ejaculates semen is deposited into the
vagina. Between 200 and 300 million sperm are in this small amount
of semen, and they 'swim' up from the vagina through the cervix
and uterus to meet the egg in the fallopian tube. Only one sperm
is required to fertilise the egg.
What is the menstrual cycle? The menstrual cycle is the way a woman's body gets
ready for the possibility of pregnancy each month. A cycle is
counted from the first day of one period (menstruation) to the
first day of the next. An average cycle is 28 days, but anywhere
from 23 to 35 days is normal. The day that bleeding starts is
counted as the first day of a given cycle. The menstrual cycle is
controlled by hormones released by the hypothalamus the pituitary
gland and the ovaries.
The menstrual cycle has four stages:
1. The menstrual phase
When a women is having her period it means that the lining of the
uterus is breaking down and slowly flowing out of her body through
the vagina over a period of days called the menstrual phase.
Menstruation is the term given to the periodic discharge of blood,
tissue, fluid and mucus from the reproductive organs of sexually
mature females. The flow usually lasts from 3 - 6 days each month
and is caused by a sudden reduction in the hormones, estrogen and
progesterone. For most of a woman's life, the egg that is released
approximately once each month will not become fertilised, so the
lining that develops each month for the possibility of a
fertilised egg cell won't be needed. Over a period of days the
blood vessels shrink and the uterus will shed the unneeded lining,
made up of a small amount of blood and tissue.
2. The preovulatory phase
The preovulatory phase (before the egg cell is released) is next
and starts as soon as the menstrual phase (the period) has ended.
During the preovulatory phase the uterine lining thickens with an
increased numbers of blood vessels. The lining of the uterus needs
to prepare itself for the possibility of supporting a fertilised
egg. An egg is also ripening in one of the ovaries in preparation
for ovulation.
3. The ovulation phase
The third phase is the ovulation phase at midcycle, which in a
28-day cycle would be day 14. A mature egg is released from one of
the ovaries during ovulation. Some women may have some slight
discomfort during ovulation usually described as a twinge or cramp
in the lower abdomen or back. Many women have no sensation that
they are ovulating. Once released the egg travels into the
fallopian tube and then begins a four to five day journey to the
uterus. The egg lives twelve to twenty-four hours in the fallopian
tube after it has been released from the ovaries and then
disintegrates if not fertilised. Sperms can survive for up to five
days inside a woman's reproductive system. The few days before,
during and after ovulation are a woman's "fertile period" - the
time when she can become pregnant. Because the lengths of
menstrual cycles vary, many women ovulate earlier or later than
day 14 of the cycle. Stress and other things can sometimes cause a
cycle to be shorter or longer. This event occurs approximately
once a month near the midpoint of a woman's menstrual cycle.
4. The postovulatory phase
Most months the egg cell simply dies in the postovulatory phase
(after the egg cell is released), the endometrium continues to
develop and the uterine glands secrete nutrient materials. If the
egg cell meets a sperm cell and is fertilised by a sperm it
attaches to the uterus. Fertilisation usually occurs when the egg
is in the fallopian tube. If a woman becomes pregnant her
menstrual cycle will stop during the time that she is pregnant. If
conception doesn't occur, the hormone levels drop. Below a certain
level of hormones, the uterine lining can no longer be maintained
and the lining of the uterus breaks down, menstruation begins, and
the cycle repeats.
How to know your fertile period?
A woman is most fertile during mid cycle. Ovulation generally
occurs 14 days before the start of the next period. To
successfully conceive, it is best to have intercourse in the
fertile window of opportunity starting at about 2-3 days before
ovulation. Usually, the fertile period in a woman, with a 28 days
cycle, extends from day 11 to day 18. It is important to keep a
track of your periods. Mark the calendar on the day you get your
period. This is Day One. Count each day until your next period
arrives. You may need to do this for three or four months to get
an accurate measure of the length and regularity of your cycle.
* If your cycles are very regular, you may be able to determine
when you ovulate: in the average menstrual cycle, ovulation occurs
14 days before the menstrual period arrives - or on day 14 of a
28-day cycle. So if you subtract 14 days from the length of your
cycle, you'll get an idea of when you ovulate.
Use the Ovulation calculator in the pregnancy section to determine
the most likely date of your ovulation.
* If your cycles are not very regular, or you'd like a more
accurate picture of your ovulation then:
1. Track your temperature: One of the indications that ovulation
has occurred is that a woman's basal body temperature increases
slightly during ovulation. You can detect this 'thermal shift' by
taking your temperature every morning at the same time before you
get out of bed. If you chart your temperature each day for a few
months, you'll begin to see a pattern that will help you predict
when you are about to ovulate. Most women's temperature increases
about a half a degree 24 to 48 hours after ovulation.
2. Watch for changes in your cervical mucus: This method does not
exactly pinpoint but gives you some indication of whether you're
in a fertile period or not. As your body prepares to ovulate, it
produces larger quantities of thin, clear cervical mucus, a
substance that smoothes the way for the sperm to meet the egg. On
your most fertile days, just before ovulation, the mucus will
appear clear, stretchy, and slippery. After ovulation, when your
fertile days are past, the mucus usually becomes thicker and then
gradually dries up.
Tips to help a woman conceive
Being healthy and having regular menstrual cycles increases the
chances of conceiving a healthy baby and carrying the baby to full
term.
Basic health tips include:
If you're under 35 and have had regular intercourse for 12 months,
or 35 or older and have been trying for six months, then it's time
to see the doctor for a fertility evaluation.
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