The vagina is a blind-ending sac which acts
as a receptacle for the sperm. Protruding into the top end of this
sac is the lower part of the uterus known as the uterine cervix.
The cervix is the entrance to the uterus. It has
a narrow central canal which the sperm must swim up to gain entrance
to the uterine cavity.
The uterus is the most changeable organ in the
body. During pregnancy it may increase in size tenfold, but afterwards
it shrinks back to near its original size. This cycle repeats with
each pregnancy. The sperm must swim along the whole length of the
uterine cavity in the non-pregnant uterus to gain access to a fallopian
tube.
The fallopian tubes are paired structures which
come off each side of the uterus and have an open end near the ovaries.
The sperm swim along the fallopian tube, where they may encounter
an ovum, or egg. Fertilisation takes place within the fallopian
tube and the resulting zygote is then moved back towards the uterus
where it continues its development into a foetus.
The ovaries are located within the abdominal
cavity and make the ova or eggs. Between puberty and the menopause,
one or more eggs are released by the ovaries each month, 14 days
before each menstrual cycle. Of course, if the egg is fertilised
the menstrual cycle is aborted and the woman becomes pregnant. Most
of a female’s eggs die before she is born. About 7 million
eggs are present in the ovaries by the fifth month of gestation,
but these have reduced to about 1 million by birth. After birth
there is further degeneration, so that only 40,000 eggs are left
by puberty. Of these only about 400 are ovulated during a woman’s
reproductive lifespan.
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