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.
- 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
- 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