S2) Development of the Reproductive Tracts Flashcards Preview

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Flashcards in S2) Development of the Reproductive Tracts Deck (26)
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Describe the relationship between the primordial germ cells and the gonad in the embryology of the reproductive system

- Primordial germ cells migrate into an indifferent gonad 

- The primordial germ cells carry the karyotype for the organism


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

- 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


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

Illustrate this

- All three systems share common caudal opening 

- Hindgut ends in dilated structure (cloaca) 

- Closed to the outside by cloacal membrane (no mesoderm


What is urogenital ridge?

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



What is the gonad derived from?

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


What are primordial germ cells?

- Special population

- “Seed” for the next generation, allocated shortly after initiation of the current generation




What are the origins and location of primordial germ cells?

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


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

- Medullary cords develop

- No cortical cords

- Thick tunica albuginea


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

- Medullary cords degenerate

- Cortical cords develop

- No tunica albuginea


Explain how the expression of SRY genes drives development of male


- Gonad (testis)

- Production of testicular hormones

- Internal genitalia (male duct system)


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

- Gonad (ovary)

- Internal genitalia (duct system – i.e. tubes & uterus) 


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

Mesonephric ducts and paramesonephric ducts develop in both male and female embryos

- Both ducts end at the urogenital sinus part of the cloaca 


What are other names for the paramesonephric and mesonephric ducts?

- Paramesonephric = Mullerian duct

- Mesonephric = Wolffian duct


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

When there is a functional testis:

- Testis produces Mullerian inhibiting hormone which suppresses Mullerian duct development

- Testis produces androgens which supports Wolffian duct 


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

When there is not a functional testis:

- No suppression of Mullerian duct development (no Mullerian inhibiting hormone)

- Wolffian duct degenerates (no testes androgens)


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

- Exogenous androgen: supports Wolffian duct

- No Mullerian inhibiting hormone: Mullerian ducts develop (no testes)


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

- Testosterone receptors don’t work: Wolffian ducts degenerate

- MIH present: Mullerian ducts degenerate



Outline the development of the Wolffian duct

- Acts as duct for the embryonic kidney

- Drains into the urogenital sinus

- Surplus to requirement once true kidney develops 


Describe the maintenance, conversion and migration of the mesonephric duct

- Maintained by testis-derived androgens

- Converted into the vas deferens and epididymis

- Migrates with the testis as it descends 


Describe the caudal and cranial development of the paramesonephric ducts

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 


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

Basic components:

- Genital tubercle (GT)

- Genital folds

- Genital swellings 


Outline the development of the external genitalia in males

- 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 


Outline the development of the external genitalia in females

- No fusion: development of labia majora & minora

- GT develops into clitoris

- Urethra opens into the vestibule 


Describe the descent of the testes

- 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


Describe the descent of the ovaries

- Gubernaculum attaches ovary inferiorly to labio-scrotal folds

- Ovary descends to the pelvis

- Uterus has developed (prevents further descent)



What is the adult derivative of the urogenital sinus?

Urogenital sinus becomes urinary bladder