Ovulation & the menstrual cycle - Narrated 3D animation

An informative video of the biological processes behind the menstrual cycle. The video is titled "The Normal Female Reproductive System" and is produced by Schering-Plough

To understand the various ways
that medical science

can assist reproduction,

it is important to understand
how the reproductive system

functions in both sexes,
because the cause of infertility

often lies equally with
both men and women.

The main players in the
female reproductive cycle

are the pituitary gland,
the ovaries, and the uterus.

Their activities are
closely coordinated.

Each month one or other ovary
releases a single egg.

An event known as ovulation.

It is brought about by a
series of complex interactions

between the pituitary gland,
the ovaries, and the uterus.

The pituitary gland is itself
under the control

of the small area of the brain
known as the hypothalamus.

A new menstrual cycle begins
when the nerve cells

of this center secrete a
hormone called

gonadotropin-releasing hormone,
GnRH,

into the network of
blood vessels

which surrounds
the pituitary gland.

Stimulated by pulses of
gonadotropin-releasing hormone,

cells in the pituitary gland
secrete another hormone,

follicle stimulating hormone,
or FSH.

FSH travels in the blood stream
reaching the ovaries.

There, it stimulates the
formation and growth

of an ovarian follicle
in one or other ovary.

The follicle consists of an egg,
a number of surrounding cells,

which secrete estrogen hormones,
and fluid.

FSH helps the egg to mature
and prepares it for release.

As the follicle matures,
the hypothalamus

increases secretion of GnRH.

This in turn stimulates the
pituitary to secrete

a second hormone
which acts on the ovary.

This is luteinizing hormone,
or LH.

Toward the middle
of the cycle

there is a sudden peak
in the blood level of LH.

This acts as the trigger
for ovulation.

Within minutes of its release
the egg is guided by suction

through the fringed opening
of the outer end

of the fallopian tube.

Starting it on a journey
which will take 5 or 6 days

as it passes down
the tube and finally

reaches the cavity of the uterus.

Meanwhile, after the
follicle ruptures,

it is converted into this
yellowish body

known as the corpus luteum.

Cells of the corpus luteum
secrete the hormone progesterone,

which brings about
important changes

in the lining of the uterus
preparing it for possible pregnancy.

In fact, the
lining of the uterus,

known as the endometrium,
undergoes changes in response to

hormone levels during the cycle.

In the first half of the cycle,
known as the follicular phase,

the developing follicles secrete
increasing amounts

of estrogen hormone
which encourages

regeneration of the endometrium.

After ovulation
there are important changes

in the endometrium
aimed at making it suitable

to receive a fertilized egg.

These changes are
brought about by

a secretion of progesterone
from the corpus luteum.

This secretion of progesterone
is maintained for several days.

But if the egg is not
fertilized in that time,

the corpus luteum withers and
falling levels of pregesterone

and estrogen trigger the
shedding of the uterine lining

as the menstrual flow.

The cycle then starts again.

But if the egg is fertilized,
no menstruation occurs

as the corpus luteum
continues to function,

secreting progesterone
during the first

3 months of the pregnancy.

Thereafter, numerous changes
occur to support the developing embryo.