Development Of The Repoductuve Tracts Flashcards
What are the three germ layers and what do they produce?
Ectroderm -> skin and nervous system
Mesoderm: skeletal muscle, bone, heart
Intermediate -> urogenital
Sphlanchnic -> covers organs
Somatic -> connective tissue
When does embryonic folding occur and what does it create?
4th week after fertilisation
Creates a cavity inside the embryo with a gut tube suspended in intraembryonic coelom -> splanchnic mesoderm -> somatic mesoderm -> dorsal Mesentery -> amniotic cavity above and yolk sac below
What does the hindgut initially end in?
Dilated structure - the cloaca, closed to the outside by the cloacal membrane
What region gives rise to both the embryonic kidney and the gonad? Which germ layer does it come from specifically?
Urogenital ridge
From the intermediate mesoderm (gonad also from primordial germ cells)
Where do primordial germ cells arise and where do they migrate to?
Arise in the yolk sac and migrate into the retroperitoneum (where germ cell tumours can occur) along the dorsal Mesentery
Describe the development of the gonad, what determines differentiation and what are the two main differences between ovaries and testis?
Y influence causes primordial germ cells to develop medullary cords (-> rete testis) and a thick tunica albuginea with no cortical cords
Absence of Y causes PGCs to develop cortical cords (-> ovarian follicles) but no tunica albuginea and medullary cords to degenerate
What drives development of internal genitalia?
Y chromosome expresses SRY gene (sex determining region) drives development of gonad, production of testicular hormones and internal genitalia (male duct system -> epididymis and vas deferens)
Females: primordial germ cells do not carry Y chromosome -> development of gonad (ovary) and internal genitalia duct system (tubes, uterus and parts of vagina)
Internal genitalia ducts development
Both begin with mesonephric (Wolffian) and paramesonephric (Mullerian) ducts
Both end at the urogenital sinus part of the cloaca
If there is a functioning testis then:
- Mullerian inhibiting hormone is produced and suppresses development of paramesonephric duct
- androgens support development of mesonephric duct
If there is no functioning testis:
- no suppression of paramesonephric development
- no androgens so Wolffian duct degenerates
How could both paramesonephric and mesonephric ducts develop?
If there is exogenous androgen exposure then Wolffian duct develops but no testis so no MIH so MUllerian duct develops (in female)
What’s androgen insensitivity syndrome?
Receptors for testosterone don’t work so Wolffian ducts don’t survive but still produce MIH so no Müllerian ducts = no ducts (in male)
What initially acts as a duct for the embryonic kidney and what does it drain into?
The mesonephric duct drains into the urogenital sinus (future bladder)
What does the mesonephric duct become?
Vas deferens and epididymis (maintained by androgens) migrates with testis as it descends
VD- transports sperm from epididymis to ejactulatory ducts
Where are paramesonephric ducts located and what do they become?
Invagination of the epithelium of the urogenital ridge, make contact with the cloaca and open into the abdominal cavity cranially
-> uterine tubes, uterus (including cervix)
Intermediate mesoderm of PD creates superior (+ endoderm of sinovaginal bulbs) -> vagina
What is created of the external genitalia at 7 weeks?
Genital tubercle Internal to external Urogenital sinus Genital fold Genital swelling
Anus
Development of the Male external genitalia
12 weeks Male:
Genital tubercle elongates
-> glans penis
Genital folds FUSE (wrap around urethra) -> spongy mesoderm
Genital swelling fuses -> scrotum
Influence of testis-derived androgen hormones e.g. dihydrotesosterone (most potent)
