Sexual Development

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Sexual Development Differentiation
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Sex Gender
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Sex and Gender

• Sex
• genetic sex - chromosomes
• anatomical sex - internal and external genitalia
• sexual identity - ones identity as male or female

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Sex and Gender

• Gender
• social meaning attached to being male or female
• gender identity - sense of being male or female
• gender role - expectations about how a male or
  female should behave

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SCIENTIFIC BASIS OF FERTILITY
OVARIAN DIFFERENTIATION
SEX DIFFERENTIATION TESTIS
SPERMATOGENESIS AND SPERM TRANSPORT
FOLLICULAR GROWTH AND OVULATION
SPERM - OOCYTE FUSION
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Gender identity is the end result of genetic
hormonal and morphologic sex as influenced by the
environment
Genetic sex (chromosome )

Gonadal sexual (testis, ovaries)

Hormones affecting sex development of fetus

Hormone production at Puberty
External genitalia
CNS
Sex assignment and rearing
Gender identity
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Normal Prenatal Development Genetics

• Chromosomes
• each human cell contains 46 chromosomes,
  occurring in pairs
• 23 pairs of chromosomes
• 22 autosomes (determines e.g., hair color)
• 23rd pair are the sex chromosomes
• male XY
• female XX

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Normal Prenatal Development Genetics.
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Normal Prenatal Development Genetics.

• Germ cells
• male sperm - contains X or Y
• female ovum - contains an X
• Y chromosome contains less genetic material
  than X chromosome

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Normal Prenatal Development Genetics.

• Mother Father
• XX XY
• X X X Y
• XX XY XX XY
• female male female male

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Normal genital development

• The mammalian fetus has an inherent tendency to
  develop into a female.
• The primitive human gonad starts to develop
  between the 4th and 6th week of fetal life
  deriving from cells of endodermal origin that
  migrate from the yolk sac to the genital ridge.
• The gonad is initially bipotential and develops
  into a testis or ovary depending upon karyotype.

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Normal Sex Differentiation
Intermediate Mesoderm
WT/SF1
XX/XO
XY/XXY
Bipotential gonads
SRY SOX9
Wnt4 DAX1- Antitestis
Testis
Ovary
Leydig cell
Granulosa Cell
Theca Cell
Sertoli cell
No AMH No T
5?-R
AMH
T
DHT
Mullerian Duct
Follicles
No mullerian Duct
Wolffian Duct
Oestrogen Progesterone
Male internal genitalia
Male External Genitalia
Female Internal Genitalia
Rs
No uterus
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Male genital development
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• 6th weeks gestations, still in bipotensial gonad.
  
• Fetus has genital duct premordial (Mullerian duct
  and Wolfian duct) and axternal genitalia
  premordial .
• 8th-12th gestation, placental gonadotropin
  increase stimulate Leydig cell for testoteron
  producing and sertoli cell for Mullerian
  inhibiting factor (MIF) producing .

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Normal Prenatal DevelopmentInternal External
Genitalia

• Sexual differentiation Gonadal development
• 8 weeks gestation
• Y chromosome synthesis of H-Y antigen
• Male H-Y antigen causes undifferentiated sex
  glands to develop into testes
• Female lack of H-Y antigen causes
  undifferentiated sex glands to develop into
  ovaries

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Normal Prenatal DevelopmentInternal External
Genitalia

• Sexual differentiation Duct development
• both sexes start out with two systems
• Mullerian ducts - will develop into fallopian
  tubes, uterus, inner vagina
• Wolffian ducts - will develop into epididymis,
  vas deferens, and seminal vesicles

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• Male sexual differentiation is initiated by the
  SRY gene on the short arm of the Y chromosome.
• Under the influence of SRY, the undifferentiated
  gonad forms a testis testosterone stimulates the
  wolffian structures (epididymis, vas deferens,
  and seminal vesicles), and anti-Mullerian hormone
  suppresses the development of the Mullerian
  structures (fallopian tubes, uterus, and upper
  vagina).

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Male genital development

• Presence of Y chromosome
• Testicular hormone production
• Normal responsiveness of androgen-dependent
  tissues

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• The conversion of testosterone to
  dihydrotestosterone occurs in the skin of the
  external genitalia and masculinizes the external
  genital structures.
• Most of this male differentiation takes place by
  about 12 weeks, after which the penis grows and
  the testes descend into the scrotum.

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CAH 46 XX
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• Infants whose genitalia are obviously ambiguous
  are investigated at birth so that sex of rearing
  can be assigned.
• In many cases, however, appearances are
  deceptive
• An infant with what appears to be bilateral
  cryptorchidism might be assumed to be a boy
  because of a normal-appearing phallic structure
  but in fact may be a girl with severe virilizing
  congenital adrenal hyperplasia (CAH).

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• An apparent female infant with only slight
  clitoral hypertrophy may be a genetic male with
  severe androgen insensitivity, necessitating
  eventual removal of the testicles to avoid
  malignant degeneration.
• It is necessary, therefore, to have well-defined
  clinical criteria for the investigation of
  intersexuality

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Female genital development

• Spontaneous process independent of hormonal
  influences.
• Without Y chromosome the primitive gonads develop
  into ovaries.
• Mullerian ducts develop into female internal
  genitalia
• Lower end of vagina forms from the urogenital
  sinus
• External genitalia similarly develop
  spontaneously.

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Normal Prenatal DevelopmentInternal External
Genitalia

• Undifferentiated stage
• 0-7 weeks gestation
• male and female external genitals the same
• urogenital fold
• genital groove
• genital tubercle
• labioscrotal swelling
• male and female internal genitalia the same -
  undifferentiated sex glands

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Normal Prenatal DevelopmentExternal Genitalia
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External Genitalia
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Normal Prenatal DevelopmentInternal Genitalia
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• Male (XY)
• Testes secrete testosterone and
  Mullerian-inhibiting hormone
• testosterone - Wolffian ducts begin to develop
• Mullerian-inhibiting hormone - inhibits further
  development of Mullerian ducts - they shrink and
  degenerate
• Female (XX)
• absense of Mullerian-inhibiting hormone -
  Mullerian ducts develop
• absense of testosterone - Wolffian ducts
  degenerate

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Normal Prenatal DevelopmentInternal External
Genitalia

• Sexual differentiation Genital development
• Male (XY) testosterone causes unisex genitalia
  to develop into penis and scrotum
• testosterone converted to dihydrotestosterone
• dihydrotestosterone causes the external
  appearance of scrotum and penis
• Female (XX) absence of testosterone causes
  unisex genitalia to develop into clitoris, labia,
  vaginal opening, etc.
• NOTE The default is the develop as a female.
  Male hormones are needed to promote
  differentiation into a male

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Normal Prenatal Development The Brain

• Sexual differentiation
• Male
• Testosterone secreted ? blood ? brain
• testosterone converted to estradiol and DHT in
  the brain
• estradiol masculinizes the brain
• Female
• alpha-fetoprotein binds to estradiol
• prevents estradiol from entering the brain
• protects female brains from being masculinized by
  estradiol

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Hypospadias
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