Sex differentiation Flashcards
XX genes
female
XY genes
Male
on Y chromosome, turns
on testis-specific genes
SRY gene
Regardless of its chromosomal makeup, the early embryo is blank, it has the potential to form either testes or ovaries
bipotential (gonadal sex)
Which cells produce testosterone?
Leydig
Which cells produce produce Anti-
Müllerian Hormone
sertoli cells
sex organ that produces hormones
testes
fairly inactive; don’t
produce significant amounts of
hormones until puberty.
ovaries
How many surges of testosterone are there for babies, when do they happen and what do they affect.
2 surges.
first one is around 16 weeks after conception and influences reproductive morphology
second surge is around 8 weeks after birth and this affects the brain and reproductive behaviors
What stimulates the secretion of testosterone during the first trimester of gestation
human chorionic
gonadotropin (hCG)
produced by the placenta to maintain the pregnancy and stimulate steroidogenesis before the HPG axis is active
human chorionic
gonadotropin (hCG)
Once the gonad has differentiated, differences in hormone
secretions direct morphological changes – starting with the
internal duct system
With no hormones, the Müllerian ducts develop and the Wolffian ducts
undergo programmed cell death leading to the creation of
ovaries
develop into the fallopian tubes, uterus, and cervix.
Müllerian ducts
Leydig cells produce testosterone that binds to
androgen receptors and prevents regression of the
Wolffian duct - this becomes the
as deferens and
seminal vesicles.
Sertoli cells produce Anti-Müllerian Hormone (AMH)
which causes the Müllerian duct to
regress
Founder of modern fetal endocrinology
Alfred Jost
used fetal rabbits at an early, ambivalent stage to explore the role of
hormones in sexual differentiation
Alfred Jost
differentiates into
the glans of the penis
genital tubercle
Develops into the scrotum
abioscrotal swellings
Testosterone is converted to dihydrotestosterone (DHT) by the
enzyme
5α-reductase
a more potent androgen - it binds to the androgen receptor with a much
stronger affinity
DHT
responsible for External Morphological Sex
DHT
Internal morphology is dependent on
testosterone
External genitalia requires
DHT
Mutation in AMH gene
Develop both Wolffian and Müllerian
ducts
XY individual with stereotypical male
genitalia, but they also have fallopian
tubes and a uterus
Persistent Müllerian Duct Syndrome
Can’t convert testosterone into DHT
XY individual with testes and external
female genitalia…until puberty
5α-reductase deficiency
the most prevalent cause of intersex among
people with XX chromosomes
Adrenal glands lack CYP21A2 and do not make
cortisol or aldosterone, instead overproducing
androgens
XX individuals with ambiguous genitalia
Congenital Adrenal Hyperplasia (CAH)
the most prevalent cause
of intersex among people with XY
chromosomes
Testosterone is produced but they can’t
respond to it (lack functional androgen
receptors)
Androgen Insufficiency
Syndrome (AIS)
Have rudimentary (undescended/internal)
testes, but develop female external anatomy
Testosterone is converted to estrogen
Androgen Insufficiency
Syndrome (AIS)
Are most behaviors sex specific?
no
Sex differences in the brain are not uniformly different in any one individual
The Mosaic Brain
Your blank continually shapes your brain
environment
a region within the hypothalamus. It’s the best characterized sex difference in the mammalian brain (although this difference diminishes with age)
Sexually-dimorphic nucleus of the preoptic area (SDN-POA)
a region within the
hypothalamus. Larger in females than in males. Regulates ovulatory
cycles.
Anteroventral periventricular nucleus (AVPV)
When does the brain develop in reference to the gonads
The brain develops after the gonads
organizes the brain during critical sensitive periods, and activates it at puberty and throughout adulthood
testosterone
long-term and irreversible effects on tissues that occur during critical sensitive windows.
Organizational effects
short-term and reversible effects that occur in
adulthood (after puberty).
Transient effects of hormones on the
previously organized system.
Activational effects
First evidence that hormones permanently shape the brain and later behaviors.
It also provided the framework for discriminating two types of actions of gonadal
steroids: organizational and activational.
Phoenix et al. 1959
Organizational vs Activational Experiments
main finding of Organizational and Activational Effects in Males
Early surge of testosterone
shaped (or organized) later behavioral responses activated by testosterone
Main finding of Organizational and Activational Effects in Females
Testosterone surge at a critical period in brain
development produces a “male” brain, and the absence of that hormone during the critical period produces a “female” brain.
organizes’ the SDN-POA
testosterone
what mascinulizes the brain?
estrogen
Aromatization Hypothesis:
Developmental expression of aromatase in certain brain regions at critical time windows is required for organizational effects of testosterone.
Testosterone can be converted to:
- estrogen via aromatase
- dihydrotestosterone (DHT) via 5α-reductase
How does estrogen cause size differences in
these brain regions?
In the SDN-POA, estrogen
promotes cell survival but in the nearby AVPV it induces cell death
Only testosterone that has been converted to estrogen in the brain
plays a role in sexual differentiation. true or false
true
High levels of estrogen produced by the mother is prevented from affecting the offspring due to
Alpha-fetoprotein (AFP)
