S2) Development of the Reproductive Tracts Flashcards

1
Q

Describe the relationship between the primordial germ cells and the gonad in the embryology of the reproductive system

A
  • Primordial germ cells migrate into an indifferent gonad
  • The primordial germ cells carry the karyotype for the organism
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2
Q

Describe the differentiation of the gonad into testis / ovary and the resulting duct systems

A
  • Gonad can develop into testis (XY) or ovary (XX)
  • Testis then develop duct systems: epididymis & vas deferens
  • Ovary then develops duct systems: uterus, tubes & part of vagina
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3
Q

The development of the reproductive tract, urinary tract and GI tract are closely linked.

Illustrate this

A
  • All three systems share common caudal opening
  • Hindgut ends in dilated structure (cloaca)
  • Closed to the outside by cloacal membrane (no mesoderm
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4
Q

What is urogenital ridge?

A

Urogenital ridge is a region of intermediate mesoderm giving rise to both the embryonic kidney and the gonad

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5
Q

What is the gonad derived from?

A

Gonad (indifferent) derived from intermediate mesoderm plus primordial germ cells (extragonadal)

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6
Q

What are primordial germ cells?

A
  • Special population
  • “Seed” for the next generation, allocated shortly after initiation of the current generation
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7
Q

What are the origins and location of primordial germ cells?

A

Arise in the yolk sac and migrate into the retroperitoneum, along the dorsal mesentery

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8
Q

What features are associated when a gonad develops into the testes?

A
  • Medullary cords develop
  • No cortical cords
  • Thick tunica albuginea
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9
Q

What features are associated when a gonad develops into the ovaries?

A
  • Medullary cords degenerate
  • Cortical cords develop
  • No tunica albuginea
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10
Q

Explain how the expression of SRY genes drives development of male

A
  • Gonad (testis)
  • Production of testicular hormones
  • Internal genitalia (male duct system)
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11
Q

Explain how the absence of Y chromosome leads to development of female

A
  • Gonad (ovary)
  • Internal genitalia (duct system – i.e. tubes & uterus)
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12
Q

Identify the pair of ducts involved in the indifferent stage of the development of internal genitalia, as well as their location

A
  • Mesonephric ducts and paramesonephric ducts develop in both male and female embryos
  • Both ducts end at the urogenital sinus part of the cloaca
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13
Q

What are other names for the paramesonephric and mesonephric ducts?

A
  • Paramesonephric = Mullerian duct
  • Mesonephric = Wolffian duct
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14
Q

Describe the fate of the paramesonephric and mesonephric ducts in a normal male

A

When there is a functional testis:

  • Testis produces Mullerian inhibiting hormone which suppresses Mullerian duct development
  • Testis produces androgens which supports Wolffian duct
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15
Q

Describe the fate of the paramesonephric and mesonephric ducts in a normal female

A

When there is not a functional testis:

  • No suppression of Mullerian duct development (no Mullerian inhibiting hormone)
  • Wolffian duct degenerates (no testes androgens)
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16
Q

What happens when the fate of the ducts go wrong and there is no testis?

A
  • Exogenous androgen: supports Wolffian duct
  • No Mullerian inhibiting hormone: Mullerian ducts develop (no testes)
17
Q

What happens when the fate of the ducts go wrong and there is Androgen Insensitivity Syndrome?

A
  • Testosterone receptors don’t work: Wolffian ducts degenerate
  • MIH present: Mullerian ducts degenerate
18
Q

Outline the development of the Wolffian duct

A
  • Acts as duct for the embryonic kidney
  • Drains into the urogenital sinus
  • Surplus to requirement once true kidney develops
19
Q

Describe the maintenance, conversion and migration of the mesonephric duct

A
  • Maintained by testis-derived androgens
  • Converted into the vas deferens and epididymis
  • Migrates with the testis as it descends
20
Q

Describe the caudal and cranial development of the paramesonephric ducts

A

Paramesonephric ducts appear as invaginations of the epithelium of the urogential ridge

  • Caudally: make contact with the cloaca (urogenital sinus)
  • Cranially: open into the abdominal cavity
21
Q

Describe the features of the external genitalia at the indifferent stage of development

A

Basic components:

  • Genital tubercle (GT)
  • Genital folds
  • Genital swellings
22
Q

Outline the development of the external genitalia in males

A
  • In the male the GT elongates and develops into glans of penis
  • Genital folds fuse to form the spongy urethra
  • Influence of testis-derived androgen hormones – dihydrotestosterone
23
Q

Outline the development of the external genitalia in females

A
  • No fusion: development of labia majora & minora
  • GT develops into clitoris
  • Urethra opens into the vestibule
24
Q

Describe the descent of the testes

A
  • The testes descend under the guidance of the gubernaculum testis, into the scrotum
  • Originally located in peritoneum
  • Tunica vaginalis is a remnant of infolded peritoneum
25
Q

Describe the descent of the ovaries

A
  • Gubernaculum attaches ovary inferiorly to labio-scrotal folds
  • Ovary descends to the pelvis
  • Uterus has developed (prevents further descent)
26
Q

What is the adult derivative of the urogenital sinus?

A

Urogenital sinus becomes urinary bladder