Transcript Human sex hormones

Sexual Reproduction
Human Sex Determination
Sex Hormones
Sexual Development
Pituitary Hormones in Males
Pituitary Hormones in Females
The Menstrual Cycle
Pregnancy
Hormonal Birth Control.
Sex and reproduction are not the same thing.
Reproduction is the formation of new individuals.
Sex is a method of exchanging and
recombining genetic information.
Many organisms
reproduce without sex.
And it is possible (like
Paramecium) to exchange
genetic information
without reproduction.
Conjugation in
Paramecium results in an
exchange of genetic
information between two
cells - in effect, mating
without reproduction.
Human sex hormones - synthesized by gonads (ovaries &
testes), but regulated by pituitary and hypothalamus.
Androgens “man-makers”
Estrogens “crazy-makers”
from Latin oestrus "frenzied passion",
"frenzy, gadfly," from Greek oistros
"gadfly, breeze, sting, mad impulse."
Human Sex Determination
is Chromosomal
Females are 46 XX
Males are 46 XY
But at 6 weeks, a
human embryo is
sexually indistinct
• Under the influence of sex
hormones (the presence or
absence of testosterone is
crucial), the genitalia of male
and female embryos
gradually develop along
separate lines beginning in
the 7th week.
These external changes are paralleled by internal
changes (Müllerian & Wolffian duct systems)
1) Testosterone is the signal. Estrogens cannot act
as the signal because development occurs within the
body of the female, loaded with estrogen.
2) There is no gene for testosterone. There
are genes for the enzymes in its biosynthetic pathway.
In any case, females have all these genes and also
synthesize testosterone.
3) The sex-determining gene in the Y
chromosome (SRY) codes for a DNA-binding protein
(a transcription factor).
4) The gene for the testosterone receptor
(which is a protein, of course) is on the X
chromosome (!). The action of testosterone is also
dependent on having a functional testosterone
receptor.
5) In the absence of either testosterone or its
receptor, estrogens produce the female developmental
pattern.
Y chromosome
Developing
Spermatocytes
Interstitial Cells
LH and FSH,
released from
the anterior
pituitary,
regulate the
ovaries and
testes.
LH = Luteinizing Hormone
FSH = Follicle-Stimulating Hormone
Hypothalamus
The Hypothalamus
produces GnRH
(Gonadotropic Releasing
Hormone)
High levels of
Testosterone
inhibit the
Hypothalamus
LH
FSH
FSH and
Testosterone are
required for sperm
development
T
T
Interstitial cells
produce
Testosterone
Testosterone serves two functions:
1) Promotes sperm development
2) Produces male secondary sexual characteristics
Testosterone serves two functions:
1) Promotes sperm development
2) Produces male secondary sexual characteristics
Ova (eggs) develop within
Follicles inside the ovary.
As an oocyte matures, its follicle enlarges
After ovulation,
the
as it prepares
for release (ovulation).
follicle remains for
about 10 days, now
called the corpus
luteum.
FSH stimulates
development of a
follicle. As it
matures, follicle
cells produce
estrogens.
2) The rise in FSH stimulates
the development of a
follicle, producing a rise in
Estrogen.
1) FSH is released in
response to low
Estrogen levels at the
start of a menstrual
period.
3) Increasing Estrogen levels
stimulate the growth of the
endometrium (uterine
lining).
5) This causes the follicle
to burst, releasing the
oocyte into the Fallopian
tube (ovulation).
4) When estrogen levels
rise to a certain point, a
burst of LH is released
by the pituitary.
6) The corpus luteum
produces high levels of
progesterone, which
targets the uterine lining.
8) Gradually, levels of
progesterone and estrogen
drop, triggering loss of
uterine lining (a menstrual
period).
7) The uterine lining increases
in vascularization, preparing
for implantation of a
blastocyst.
The entire process is regulated by a series of
feedback loops (some negative, some positive)
between ovary and pituitary.
If implantation does occur,
cells surrounding the embryo
begin to release HCG (Human
Chorionic Gonadotropin)
HCG stimulates the Corpus Luteum
to remain active, continuing to
produce progesterone (maintaining
the uterine lining).
HCG stimulates the Corpus Luteum
to remain active, continuing to
produce progesterone (maintaining
the uterine lining).
The rise in progesterone
maintains the developing
pregnancy — and also
feeds back negatively to
the hypothalamus.
As a result, FSH levels do
not rise, a new follicle
does not develop, and
ovulation is suppressed
for the rest of the
pregnancy.
HCG stimulates the Corpus Luteum
to remain active, continuing to
produce progesterone (maintaining
the uterine lining).
Hormonal birth control
pills work by simulating
this aspect of pregnancy.
They maintain high
enough levels of
progesterone or estrogen
to inhibit the development
of a new follicle.
When you stop taking the
pill for 7 days or so,
progesterone drops low
enough to allow a period,
but not so low as to
stimulate FSH release.