The Reproductive System

Module
8:
The
Reproductive
System
The
Male
Reproductive
System:
Hypothalamus-Pituitary
Gonad
Axis
Sexual
Differentiation:
→
The
“Seven
Steps”
of
Sexual
Differentiation:
1.
Chromosomal
Determination:
where
the
sex
of
the
embryo
is
determined
by
its
chromosomes
(XX
for
females
and
XY
for
males)
a.
Humans
have
46
chromosomes,
including
2
sex
hormones
that
determine
an
individuals
genetic
sex
(XX
and
XY)
2.
Expression
of
the
SRY
Gene:
the
SRY
gene
is
located
on
the
Y
chromosome
and
must
be
expressed
to
initiate
the
development
of
the
male
gonads.
a.
If
the
gene
is
not
expressed
or
if
it
is
mutated,
the
development
might
not
follow
the
typical
development
pathway
3.
Development
of
Gonads:
based
on
the
presensce/absence
of
the
SRY
gene,
the
gonads
develop
into
either
testes
or
ovaries.
This
step
establishes
the
gonadal
sex.
4.
Mutation
and
Variations:
discrepancies
between
chromosomal
sex
and
gonodal
sex
can
lead
to
conditions
such
as
Complete
Androgen
Insensitivity
Syndrome
or
other
forms
of
intersex
conditions
5.
Hormone
Production:
once
the
gonads
are
formed,
they
start
producing
sex
hormones
-
testes
produce
testosterone
and
ovaries
produce
estrogen.
6.
Hormone
Reception:
the
body
must
have
receptors
sensitive
to
these
hormones
to
respond
appropriately.
a.
Ex
:
testosterone
receptors
are
necessary
for
developing
male
physical
traits.
7.
Phenotypic
Development:
this
final
step
involves
the
development
of
external
sexual
and
secondary
sexual
characteristics
based
on
the
hormones
and
their
reception.
This
leads
to
the
physical
appearance
of
maleness
or
femaleness,
often
referred
to
as
phenotypic
sex
The
Common
Axis:
GnRH
(gonadotropin-releasing
hormone)
is
produced
in
the
hypothalamus
and
its
release
is
pulsatile
which
prevents
the
desensitization
of
GnRH
receptors
in
the
pituitary
gland.
The
GnRH
stimulates
the
anterior
pituitary
gland
to
produce
LH
and
FSH
.
FSH
acts
on
Sertoli
cells
(located
within
the
seminiferous
tubules
of
the
testes
where
sperm
are
produced
to
promote
the
formation
and
maturation
of
sperm.
Seroli
cells
also
produce
inhibin
which
serves
to
reduce
FSH
production
(negative
feedback
loop) LH
targets
Leydig
cells
which
are
located
outside
the
seminiferous
tubules
and
are
not
in
direct
contact
with
sperm.
LH
stimulates
Leydig
cells
to
produce
testosterone
which
also
participates
in
a
negative
feedback
loop
with
the
hypothalamus
and
pituitary
gland
to
regulate
the
production
of
GnRH,
LH,
and
FSH
(helps
to
maintain
hormone
levels
within
appropriate
ranges).
Key
Concepts:
-
Differentiation
of
germ
cells
are
well
as
synthesis
and
secretion
of
sex
hormones
are
common
functions
of
the
ovaries
and
testes
-
Reproduction
in
both
males
and
females
is
controlled
by
the
pulsatile
secretion
of
GnRH
from
the
hypothalamus
which
controls
FSH
and
LH
secretion
from
the
pituitary
-
FSH
and
LH
govern
germ
cell
maturation
and
sex
steroid
hormone
production
in
both
males
and
females
-
Sex
steroid
hormones
regulate
FSH
and
LH
by
negative
feedback
and
are
required
for
fertility
and
secondary
sexual
physical
characteristics.
Sperm
and
Hormone
Production:
The
Testicle:
→
This
organ
has
two
main
parts:
1.
The
Testis
:
a.
There
are
hundreds
of
seminiferous
tubules
that
are
coiled
and
run
in
parallel
b.
Spermatogenesis
(the
formation
of
sperm)
occurs
in
the
tubules
c.
This
process
can
happen
throughout
the
lifetime
of
a
male
after
they
have
reached
puberty
2.
The
Epididymis
a.
Where
sperm
is
stored
and
where
they
continue
their
maturation
b.
During
a
90
process,
sperm
acquire
motility
and
the
ability
to
fertilze
an
egg.
c.
Final
maturation,
capacitation
,
occurs
in
the
female
reproductive
tract,
particularly
the
fallopian
tubes,
and
is
necessary
for
the
sperm
to
penetrate
and
fertilize
an
egg.