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0:00
Hello, my name is Dr.
Victoria Garside.
And I am an ARC DECRA Fellow
in the Department of
Anatomy and Physiology
at the University of Melbourne
in Parkville,
Victoria, Australia.
Today I will be
presenting to you
the reproductive system,
fertilization, pregnancy,
parturition, and birth.
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The process of procreation
in land vertebrates requires
interactive behaviors and
specialized genitalia
in the male and female
for fertilization.
Which is the meeting of the
sperm and an egg to occur.
As a very broad
overview, in humans,
the reproductive organs
or specialized genitalia
in the female are
the vagina: which is the
receptacle for the male organ,
the uterus: which is required
for fetal development,
and the ovaries containing
the unfertilized egg.
In the male, the
reproductive organs are
the penis: the organ responsible
for the deposition of
sperm into the female
via the vagina,
and the tests: which
house the sperm.
1:01
The process of
procreation in humans
requires specialized
interactive behaviors.
Coitus, the human sex
act has four phases.
The first phase is excitement,
where erotic stimuli prepare
the genitalia for copulation.
The second phase is
called the plateau phase,
and this is where
the changes that
occur in the excitement
phase intensify.
The third phase is orgasm,
where the changes
lead to a climax,
causing a series of
muscle contractions
accompanied by intense
pleasure sensations.
The final phase is resolution,
where the physiological
changes return to normal.
In humans, the penis
in its resting state is flaccid
and not able to penetrate
the vagina. And therefore
requires a specialized sex
act called an erection.
In an erection, the penis
stiffens and enlarges,
and releases sperm
from the ducts of
the reproductive tract
during ejaculation.
Without this process,
fertilization cannot occur.
In the excitement phase,
males have an erection.
And in the female,
there's an erection of the
clitoris and vaginal lubrication.
In both males and females,
an erection is a vascular
congestion where
the arterial blood flow into
the spongy erectile tissue
exceeds the venous outflow.
For the excitement phase,
erotic stimuli can be
tactile or
psychological stimuli.
Psychological stimuli can
vary drastically
between individuals.
For tactile stimuli,
there are erogenous zones
across the body
that have receptors
that lead to sexual arousal.
This includes regions
like the genitalia,
lips, tongue, nipples,
and ear lobes.
In the male, the erection
reflex begins with
tactile stimuli sensed by
the mechanoreceptors in the
penis or erogenous zone.
Sensory neurons signal to the
spinal integration center,
which inhibits vasoconstrictive
sympathetic input
on penile arterials.
At the same time, nitric
oxide produced by
the increased
parasympathetic input,
actively dilates the
penile arterials.
As the blood flows into
the erectile tissue,
it compresses the veins
and traps the blood,
leading to an engorgement
of the tissue.
The climax of the male sex
act coincides with emission.
The movement of sperm out of
the vas deferens
into the urethra.
And ejaculation, where the semen
is expelled outside the penis with
rapid muscle contractions
accompanied by
intense pleasure
sensations and orgasm.
This allows sperm to be
deposited into the female
reproductive tract.
The human sex act
