Download HUMAN REPRODUCTION BIOLOGY 269

Both male and female reproductive functions controlled by hormones.
We’ve already discussed some of those.
Let’s review a bit
and
Discuss some additional hormones important in reproduction.
It all starts with the pituitary gland
Pituitary gland secretes follicle stimulating hormone (FSH):
FSH stimulates follicles to
develop in ovary;
Follicles then produce
estrogen.
FSH (along with
testosterone) stimulates
seminiferous tubules of
testes to produce sperm
Estrogen:
a)
Stimulates development of
female sexual characteristics
b)
Stimulates contractions of
oviduct
c)
Stimulates endometrium of
uterus to proliferate
d)
Inhibits secretion of more FSH
from pituitary
(Seminiferous tubules don’t
secrete any other hormones,
so FSH secretion by pituitary
remains constant)
Pituitary gland secretes luteinizing hormone (LH):
LH stimulates ovulation, then
stimulates follicle to develop
into corpus luteum; this then
secretes progesterone
LH stimulates interstitial
cells of testes to secrete
testosterone
Progesterone
Testosterone
a)
Continues to inhibit secretion of
FSH from pituitary
a)
Stimulates development of
male sexual characteristics
b)
Keeps endometrium of uterus
ready for embryo implantation
b)
Does not inhibit LH secretion
by pituitary, so LH remains
constant
c)
Inhibits contraction of muscle
(myometrium) of uterus
If fertilization does not occur:
If fertilization occurs:
Corpus luteum stops secreting
progesterone and degenerates.
The embryo begins to develop
its placenta, which secretes
human chorionic gonadotropin
(HCG).
As levels of progesterone fall,
menstruation occurs as the
myometrium (muscle) of the
uterus contracts and the
functional layer of its
endometrium falls off.
HCG stimulates corpus
luteum of ovary to continue
secreting progesterone; this
inhibits menstruation and
inhibits the pituitary from
secreting FSH, so another
follicle will not start to develop
The pituitary is no longer
inhibited and begins to secrete
FSH again
The pituitary gland secretes two more hormones involved in
reproduction:
During pregnancy, pituitary
secretes prolactin; this
causes the breast to develop
milk-secreting glands and
begin the production of milk
The pituitary also secretes oxytocin
which has a number of both
physiological and psychological effects.
During both menstruation and
childbirth, the pituitary secretes
oxytocin, which causes myometrium
(muscle) of the uterus to contract.
If labor and childbirth do not normally
develop and/or progress quickly
enough, additional oxytocin may be
used to “induce” or speed up labor
During breastfeeding, sucking
on the nipple causes pituitary to
secrete oxytocin which causes
smooth muscle in the breast to
contract and express the milk.
Increased levels of oxytocin also leads to feelings of both emotional
and sexual attraction: “The hormone of love”.
Oxytocin levels increase sharply
during early stages of attraction and
sexual arousal. This starts a “positive
feedback loop” which increases your
receptivity even more and increases
your sensitivity to sexual signals from
others and to sexual stimulation.
Oxytocin continues to rise during sexual
activity, eventually triggering both the
muscular contractions and the positive
emotional responses of orgasm.
Oxytocin: significant differences between men and women
Women secrete more oxytocin in
response to emotional and verbal cues;
Men secrete more oxytocin in response
to physical and visual cues.
Women produce more oxytocin
than men during arousal and
intercourse, but also require
these higher levels to get the
same level of arousal and to
reach orgasm.
Oxytocin: significant differences between men and women
Oxytocin levels:
Fall rapidly in men after intercourse,
but
Stay elevated much longer in women.
This has been linked to women’s increased desire for a
continued connection with her mate after intercourse, and to
men’s relative lack of this desire.
Decreased levels of oxytocin result in
decreased levels of sexual response in
both men and women
and
Supplemental oxytocin can be used to
increase this
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