Ovulation in humans
in humans, ovulation happens approximately
14 days before the start of the next
menstrual cycle. However, normal
ovulation can occur as early as around day
8, or as late as day 20 or beyond. The
timing of ovulation depends on the length
of the woman's menstrual cycle, hence a
woman with a particularly short cycle will
ovulate earlier while a woman with a long
cycle will ovulate much later. Some women
can feel a slight pain in their lower
abdomen, known as mittelschmerz or
"intermenstrual pain".
In every menstrual cycle some ovarian
follicles begin maturation, but mostly
only one will end as a graafian follicle,
growing rapidly under the influence of fsh
and lh at the end of its development to a
diameter of approximately 15 mm, forming a
"blister" on the surface of the ovary with
a small spot without blood vessels, the
"stigma". Enzymatic processes and the
growing pressure of its fluid-filled
antrum lead to its rupture.
By this time, the oocyte has undergone its
first meiotic division, leading to two
cells of very different size: the
secondary oocyte - containing all of the
cytoplasmic material of both
daughter-cells - and the first polar
body.
The second meiotic division follows at
once without dna replication but will be
arrested in the metaphase and will so
remain until fertilization. The spindle
apparatus of the second meiotic division
appears at the time of ovulation. If no
fertilization occurs, the oocyte will
degenerate approximately 24 hours after
ovulation.
At ovulation, the mucous membrane of the
uterus - termed the functionalis - has
reached its maximum size, and so have the
endometrial glands, although they are
still non-secretory.
Knowing about the time of ovulation is
critical for all forms of natural family
planning, though the rhythm method is not
typically considered a reliable method of
birth control.
Recent research suggests that in some
women, ovulation may occur more than once
during each menstrual cycle, making it
difficult for a woman to be aware of
exactly when she is fertile. This
discovery is considered by some to be a
likely explanation for pregnancies caused
by sexual intercourse when a woman is sure
she should not be ovulating. Another
explanation is, of course, that the woman
has mistakenly assumed that she ovulates
on day 14, when in fact, she ovulates
earlier or later in her cycle.
