Embryology Flashcards
when does gastrulation occur?
week 2 (2 layers) > week 3 (3 layers)
what happens in gastrulation?
formation of the trilaminar disc
invagination of the epiblast cells through the primitive streak to form the definitive endoderm and mesoderm
mesoderm is then organised into 3 main groups
- paraxial
- intermediate
- lateral plate
what 2 types of folding occur in development?
lateral folding (roll up into a tube) cranial folding (top and bottom ends of tube curve up towards middle)
do the urinary and genital systems develop together?
sort of
both arise from intermediate mesoderm and excretory ducts enter a common cavity (cloaca - will become urethra)
what are the 3 main bits of the urogenital system embryologically?
pronephros (degenerates quickly after forming)
mesonephros (functional)
metanephric (kidney)
how does the indifferent gonad form?
primordial germ cells form in the yolk sac and migrate via dorsal mesentery to the intermediate mesoderm during week 4-6
coelomic epithelium in intermediate mesoderm proliferates and forms genital ridges and somatic support cells
somatic support cells envelop the PGCs
what are the 2 main primitive ducts in the urogenitary system development and where do they connect?
mesonephric (wollfian) duct
paramesonephric (mullernian) duct
both connect to the posterior wall of urogenital sinus
what is the ambisexual phase and when does it occur?
phase where male and female anatomy is the same, before sexual differences are seen
occurs up to week 7
what stimulates the development of male anatomy?
SRY protein
SRY = sex determining region of Y chromosome
what happens in the presence of SRY?
somatic support cells develop into sertoli cells and produce medullary cords which engulf PGCs
medullary cords connect to mesonephric duct via rete testis
cords loose connection with cortex of indifferent gonad due to loss of tunica albuginea causing cortex to degenerate while the medulla develops
how are sertoli cells involved in male development?
secrete AMH (anti mullerian hormone) which causes degeneration of the paramesonephric (mullerian) duct stimulate leydig cells which secrete testosterone which induces formation of epididymus, vas deferens, seminal vesicles 5 alpha reductase turns testosterone into Dihydrotestosterone (DHT) which induces male specific external genitals and prostate development
what does the mesonephric duct form?
epididymus
vas deferens
what is persistent mullerian duct syndrome?
mutations of AMH or AMH receptor genes causing failure of paramesonephric duct degeneration therefore female features persist - uterus, vagina and uterine tubes - testes in ovarian location - male external genitalia
name the layers through which the testes descend?
peritoneum subserous fascia transversalis fascia transversus abdominus muscle internal oblique external oblique
what is the vaginal process?
invagination of parietal peritoneum over testicle as it descends through layers
where an inguinal hernia protrudes through
at what level do the testes originate?
T10
what pulls the testes caudally?
gubernaculum
what is the name for an undescended testicle?
cryptochidism
which 3 accessory glands sprout near the junction of mesonephric duct and urethra and when does this happen?
prostate (endodermal invagination from urethra) bulbourethral gland (endodermal invagnation from urethra) seminal vesicle (from mesonephric ducts) occurs at week 10
how does female gonadal development differ from male?
no SRY so no male lineage stimulated so no sertoli cells so no AMH so the paramesonephric duct persists
germ cells differentiate into oogonia then primary oocytes
somatic support cells differentiate into granulosa cells which surround primary oocytes forming primordial follicles in the ovary
cortical cords in cortex develop and medulla degenerates
function of primordial follicles and thecal cells in female development?
influence of ovarian oestrogens and from maternal sources stimulates formation of the female external genitalia and development of paramesonephric ducts
what does the paramesonephric duct become?
uterine tubes
uterus
superior vagina
what are the 3 parts of the paramesonephric duct?
cranial (opens into coelomic cavity)
horizontal (crosses mesonephric duct)
caudal (fuses with paramesonephric duct on opposite side)
how do the paramesonephric ducts form the uterovaginal canal?
paramesonephric ducts fuse together caudally at the urogenital sinus then start to zip up
they stop at a point and the connection between the two ducts degenerates forming one big cavity
end of the ducts forms the carvix
the vaginal lumen is created via vacuolization of the paramesonephric portion portion of the vagina and the sinovagital bulbs and the fornices
the vagina is made of what types of tissue?
endoderm and mesoderm
types of problems with female development?
double uterus and double vagina (ducts never fuse) double uterus (only join but dont zip up) bicornate uterus (septum doesnt fully degenerate) separated uterus (septum doesnt degenerate) unicornate uterus (only 1 duct) cervical atresia (uterus doesnt connect to vagina cavity)
external genitalia is the same in both sexes until which week?
week 7
how does external genitalia develop in males?
spongy urethra forms proximal to distal zipping of urethral groove
ectodermal ingrowth at tip of the gland penis which meets spongy urethra
prepuce (foreskin) is formed by circular ingrowth of ectoderm around the periphery of glans (week 12)
what does the genital tubercle become in males and females?
males = glans penis females = clitoris
