Animal Science 434 Reproductive Physiology

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Animal Science 434Reproductive Physiology

• Lec 5 Embryogenesis of the Pituitary and Sexual
  Development

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Development of the Pituitary Gland
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Germ Cell Migration
Migration begins by the 4 week of gestation in
cow and human.
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Migration from endoderm through mesoderm.
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In birds the migration is via the blood stream.
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Fetal Kidneys

• Pronephros
• regresses
• Mesonephros
• portions of reproductive tract
• Metenephros
• Adult kindney and urinary ducts

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Development of Mesenephros and Metenephros
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Jost Experiments
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Sex Determination The Jost Paradigm
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Chromosomal Sex

• Sex is environmentally determined
• sea worms, fish
• Single Pair of sex chromosomes
• mammals, some but not all vertebrates
• Multiple sex chromosomes
• invertebrates, insects, reptiles
• Haplodiploidy
• bees, spiders

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Chromosomal Sex

• A. Drosophila
• Sex depends on the number of X chromosomes
• X or XY or XO ? Male
• XX or XXX or XXY ? Female
• B. Human (mammals)
• XY or XXY or XXYY or XXXY or XXXXY ? Male
  (testis)
• XX or XXX ? Female (ovary)
• XO ? Female with incomplete ovarian development
• XXY or XXYY or XXXY or XXXXY ? testis but
  impaired sperm production
• C. Conclusion
• The primary gene that controls testicular
  differentiation is on the Y chromosome in mammals.

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The Y Chromosome
A. Region coding for testicular development

• Short arm of Y chromosome

• H-Y Antigen
• no longer believed to be involved
• SRY
• Codes for a DNA binding protein
• acts as a transcription factor or assists other
  transcription factors
• the gene products which are transcribed regulate
  primary sex chord differentiation (formation of
  seminiferous tubules), androgen production and
  Anti-Mullerian Hormone (AMH) production
• in the absence of the SRY protein, primary sex
  chord regress and secondary sex chords (egg
  nests) develop

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The Y Chromosome Cont.

• B. Other genes on the Y chromosome
• Spermatogenesis
• androgen production
• long bone growth

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SRY and Birds

• Birds
• females ZW, males ZZ
• W chromosome determines sex
• SRY is found on the Z chromosome !
• SRY is not the only sex determining gene in
  animals

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Gonadal Sex
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Testis Determining Factor (SRY gene product)
XY Male
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Testicular Development
Mesonephric Tubules
Mesonephric Duct (Wolffian Duct)
Rete Tubules
Mullerian Duct
Tunica Albuginea
Undifferentiated Sex Chords
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Mesonephric Tubules
Rete Tubules
Wolffian Duct

• Primary, Epithelial or
• Medullary Sex Chords
• Primordial germ cells
• Sertoli Cells

Mullerian Duct
Tunica Albuginea
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Hormonal Sex
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Testis Determining Factor (SRY gene product)
XY Male
Testes develop
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Wolffian Duct Cells
Nucleus
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Testis
T
TR
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Rete Tubules
Efferent Ducts (Vas Efferentia)
Epididymis
Seminiferous Tubules
Ductus Deferens
Tunica Albuginea
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Testis Determining Factor (SRY gene product)
XY Male
Testes develop
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Vas efferentia
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Female Development
No TDF
Testes Determining Factor
XX Female
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Ovarian Development
Regressing Tubules
Mullerian Duct
Epithelial Sex Chords
Future Ovarian Cortex
Wolffian Duct
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Regressing Tubules
Mullerian Duct
Regressing Epithelial Sex Chords
Future Ovarian Cortex
Regressing Wolffian Duct
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Regressing Tubules
Primordial Follicles
Mullerian Duct
Regressing Epithelial Sex Chords
Future Ovarian Cortex
Regressing Wolffian Duct
Secondary or Cortical Sex Chords (egg nests)
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Primordial Follicles
Mullerian Duct
Ovarian Medulla
Ovarian Cortex
Regressing Wolffian Duct
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Development of the Uterus, Cervix and Vagina
Mullerian Duct
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Fused Mullerian Duct
Hymen
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Reproductive tract develops outside
the peritoneum!
Broad Ligament Development (transverse anterior
section)
Ovary
Regressing Wolffian Duct
Mullerian Duct
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Ovary
Regressing Wolffian Duct
Mullerian Duct
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(Posterior Transverse Section)
Genital Fold (Future Broad Ligament)
Regressing Wolffian Duct
Mullerian Duct
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Testis Determining Factor (SRY gene product)
No TDF
XX Female
XY Male
Testes develop
Ovaries Develop
No AMH
No Testosterone
Sertoli cells secrete anti-mullerian hormone (AMH)
AMH causes leydig cells to differentiate
Degeneration of Mullerian duct
Mullerian ducts become the oviducts, uterus,
cervix and part of the vagina
Degeneration of Wolffian duct
Testosterone
Development of male duct system
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Phenotypic Sex
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Testis Determining Factor (SRY gene product)
XY Male
Testes develop
Sertoli cells secrete anti-mullerian hormone (AMH)
AMH causes leydig cells to differentiate
Degeneration of Mullerian Duct
Testosterone
Development of male duct system
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Wolffian Duct Cells
Nucleus
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Testis
T
TR
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Accessory Sex Glands and External Genitalia Cells
Nucleus
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Testis
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T
DR
5??- Reductase
Prostate, Cowpers Gland
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Significance of DHT

• Androgen receptor has a higher affinity for DHT
• Can get effects with low levels of circulating
  testosterone
• Secondary sex characteristic tissue in the male
  expresses 5a-reductase

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External Genitalia Differentiation
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Testis Determining Factor (SRY gene product)
No TDF
XX Female
XY Male
Testes develop
Ovaries Develop
No AMH
No Testosterone
Sertoli cells secrete anti-mullerian hormone (AMH)
AMH causes leydig cells to differentiate
Degeneration of Mullerian duct
Mullerian ducts become the oviducts, uterus,
cervix and part of the vagina
Degeneration of Wolffian duct
Testosterone
Development of male duct system
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Brain or Behavioral Sex
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Brain and Behavioral Sex Differentiation
Genetics
Gonadal Steroid Hormones
Sexual Behavior
Brain Structure
Experience
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Brain Sexual Differentiation

• Rat female
• Give testosterone shortly after birth
• fail to copulate or cycle like female as adult
• Sexually dimorphic nucleus
• Human male and female differences in behaviors
• aggression
• childhood play
• 3D visual rotation

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Decent of the Testis into the Scrotum
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Testicular Descent
Growth of testis
Fusion of the tunica albuginea and peritoneum to
form the visceral tunica vaginalis
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Front View
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Rapid growth of gubernaculum
Testis is pulled down to the inguinal ring.
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Gubernaculum regresses
Testis pulled into scrotum
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Continued regression of Gubernaculum
Testis pulled deeper into Sscrotum
Vaginal Process attaches to Scrotum
Space between Visceral and Parietal T.V. is
continuous with Peritoneum
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Failure or Problems With Testicular Descent

• Cryptorchid
• unilateral
• bilateral
• Inguinal Hernia

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Inguinal Hernia
Loop of Intestine
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Abnormalities in Development
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The Freemartin in Cattle

• Female born twin to a bull
• Extra embryonic membranes fuse to form a common
  chorion
• Comon blood supply
• Both fetuses share a common hormone milieu
• testosterone
• anti-mullerian hormone
• Animals are chimeric
• both express TDF

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Testicular Feminization in an XY Individual

• No androgen receptor
• Testis
• No testosterone response so no Wolffian duct
  development
• AMH present so mullerian ducts regress
• External genitalia is female due to lack of
  androgen

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5 ? Reductase Deficiency in an XY Individual

• testis
• AMH present so Mullerian ducts regress
• some Wolffian ducts
• psuedovagina and female external genitalia
• at puberty may differentiate into phenotypic male

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Describe the development of the reproductive
tract and/or gonad in an undifferentiated

• embryo that is castrated.
• female embryo (XX) that has a testis transplated
  next to the right gonad.
• female embryo (XX) that has a testosterone
  implant placed next to each gonad.