Development of the Reproductive Tract Flashcards
What are the 3 germ layers
Ectoderm = skin, brain, NS
Mesoderm = CT, muscle, CVS
Endoderm = inner lining, liver, pancreas
What is gastrulation?
Formation of the 3 germ layers
Blastula (2 layers) to gastrula (3 layers)
What happens to the embryo in its 4th week of development?
Folds
Creates cavity with a gut tube suspended in it
The development of the gonads and internal genitalia happens from what part of the mesoderm?
Intermediate
The gut tube is developed from the pinching of what?
Yolk sac is pinched as the embryo folds
What is the primitive gut tube?
Precursor to the respiratory and GI system
Suspended inside the peritoneal cavity (lined by parietal peritoneum)
Surrounding the gut tube = visceral peritoneum
3 regions = foregut, midgut, hindgut
Briefly describe how a reproductive system is made
Start with indifferent gonads, indifferent duct system, indifferent external genitalia
Primordial germ cells arrive at indiff gonad
Karyotype of PGC determines what gonad becomes
If testes devel, androgens present, ducts = epididymis, vas deferens devel, EG = penis, scrotum
If ovary devel , ducts = uterus, tubes and part of vagina devel, EG = vulva
To begin with what do the repro, urinary and GI tract share?
Common caudal opening in hidgut, ends in a dilated structure = cloaca
Initially the cloaca is closed by cloacal mem
What is the urogenital ridge?
Region of intermediate mesoderm giving rise to embryonic kidney and gonad
What is the gonad derived from?
Intermediate mesoderm + extragonadal PGCs
What is the mesonephros?
Embryonic kidney
Contains mesonephric duct
Outline primordial germ cells
Arise from wall of yolk sac
Their karyotype determines the diff of indiff gonads
Migrate along dorsal mesentery to indiff gonad
What happens to the indiff gonad when XY PGCs arrive?
PGCs arrive = medullar of gonad diffs to seminiferous epithelium, PGCs primed for gametogenesis later
What happens to the indiff gonad when XX PGCs arrive?
PGCs arrive = cortex devel into primordial follicles (later to be ovarian follicles)
In the devel of internal genitalia, how are the male and female duct systems different?
Male = mesonephric duct
Female = paramesonephric duct
What decides the fate of the duct system in males?
Testes prod Mullerian inhib hormone = supress paramesonephric duct devel
Testes prod androgens = support mesonephric duct devel
What decides the fate of the duct system in female?
No testes = no Mullerian inhib hormone = paramesonephric duct devel
No testes = no androgens = mesonephric duct degenerates
How can devel of the ducts go wrong?
Exogenous androgen = support mesonephric ducts
Receptors for testosterone don’t work = mesonephric ducts don’t survive
Outline the development of the mesonephric duct
Mesonephric duct first acts as duct for embryonic kidney in both males and females
Drains into urogenital sinus
Urogenital sinus becomes urinary bladder
Surplus to requirement once true kidney develops
Converted to vas deferens and epididymis and migrates with testis as it descends
Outline the development of the paramesonephric duct
Appear as invaginations of epithelium of urogenital ridge
Travel caudally to make contact with the cloaca (urogenital sinus)
Cranially open to abdo cavity
Outline the development of the uterus
Fusing of the paramesonephric ducts
What are the 2 tissue that give rise to the vagina?
Paramesonephric duct tissue
Sinovaginal bulb tissue
What are the basic components for the external genitalia?
Genital tubercle
Genital folds
Genital swellings
How does the urogenital sinus form?
Rupture of the cloaca
Describe the devel of male external genitalia
Genital tubercle elongates into glans penis
Genital folds use to form spongy urethra
Fusion driven by dihydrotestosterone
Describe the devel of female external genitalia
No fusion = vulva
Genital tubercle devel in clitoris
Outline the descent of the testis
Testes behind peritoneum
Gubernaculum attaches it to labial/scrotal folds = leads it down
If the processes vaginalis remains patent what occurs?
Indirect inguinal hernia
Outline the descent of the ovaries
Gubernaculum attaches it to labial/scrotal folds = leads it down
Only descends as far as pelvis = uterus forms mechanical barrier
