repro embryology Flashcards
what forms the urogenital system
intermediate plate mesoderm
how is the timeline for reproductive organogenesis different to the other systems
extends beyond 8 weeks
extends beyond post-natal period
which system forms the template for parts of the reproductive system
urinary system
the 2 systems have close embryological links
how many sets of kidneys develop
3
what are the 3 sets of kidneys that develop embryologically
pronephros - cervical region, vestigial
mesonephros - thoracolumbar region, briefly functional
metanephros - pelvic region, functional
each acts as a template for subsequent stage
which set of kidneys does the reproductive system develop from
mesonephros
when does genital (gonadal) ridge formation occur
week 5-6
what occurs during genital ridge formation
6wks - mesonephros forms along ovoid structure in association with thoracic and upper lumbar vertebrae
medial part of mesonephrc ridge becomes thickened to form a gential ridge
germ cells and the genital ridge
germ cells migrate into the genital ridge to form the indifferent gonad
stem cells embed into primitive sex cords (formed from mesenchyme of genital ridges)
where do the migrating stem cells come from
yolk sac via dorsal mesentery
what happens if the germ cells don’t migrate
no gonads are formed
why is it known as an indifferent gonad at this stage
there is no differentiation yet between male and female
formation of the paramesonephric duct
epithelium of the mesonephros invaginates to form a tube
this tube becomes the paramesonephric duct
where does the paramesonephric duct develop
lateral to developing gonads and existing mesonephric duct
describe the shape of the paramesonephric duct
funnel shaped cranial end
opens into peritoneal cavity
caudally, crosses ventral to mesonephric ducts
this projects into the dorsal wall of urogenital sinus
3 primitive structures of reproductive system
indifferent gonad
mesonephric duct
paramesonephric duct
alternative name for mesonephric duct
Wolffian duct
alternative name for paramesonephric duct
Mullerian duct
what do the primitive reproductive structures develop into in males
indifferent gonad - testes
mesonephric duct - vas deferens, seminal vesicles grow as outpouchings from mesonephric duct
paramesonephric duct - disappears
urogenital sinus forms bladder, urethra and prostate
what do the primitive reproductive structures develop into in females
indifferent gonad - ovaries
mesonephric duct - disappear
paramesonephric duct - fallopian tube, uterus and cervix
urogenital sinus forms bladder and lower part of vagina
what determines whether the indifferent gonads become male testes or female ovaries
chromosomes - XX or XY
Y chromosome has an SRY region - sex determining region
what protein does SRY encode for
encodes for a protein called TDF - testis determining factor
which cells express the SRY
primordial supporting cells (within the sex cords of the indifferent gonad) express the SRY
what are the actions of TDF
makes indifferent gonad develop into a testis
transforms primordial cells into sertoli cells
what do sertoli cells secreting
MIS - mullerian inhibiting substance
what are the actions of MIS
causes paramesonephric duct to degenerate
causes cells in interstitium to transform into Leydig cells
what do Leydig cells secrete and what is the result of this
testosterone
helps in further development of male external genitalia
timeline for testis development - wk5-6
wk5 - 1y sex cords, medulla and cortex
wk6 - primordial germ cells incorporated into 1y sex cords
timeline for testis development -wk7
TDF stimulates 1y sex cords -> extend into medulla -> seminiferous cords -> tubules
seminiferous cords branch, ends anastamose -> rete testis of medulla
mesothelium lost when thick capsule forms (tunica albuginea)
mesenchyme between cords gives rise to interstitial cells of Leydig
timeline for testis development -wk8
Leydig cells produce testosteroneand other hormones -> stimulates masculine differentiation of mesonephric ducts and external genitalia
paramesonephric duct degenerates in males
where do the seminal vesicles grow from
outgrowth from caudal end of mesonephric duct
where does the prostate grow from
outgrowth from urethra (from urogenital sinus)
why does the indifferent gonad become the ovary in females
no SRY region, absence of TDF
gonad develops into an ovary by default
development of the ovary, up to wk10
1y sex cords degenerate, leaving primordial germ cells
wk 10 - 2y sex cords develop from surface epithelium, primordial germ cells are incorporated
development of the ovary - wk16
primordial germ cells bud off with single surrounding layer of cortical cord cells to form primordial follicles
active mitosis of these early primordial follicles to form additional follicles
development of the ovary - 7mths-birth
7mths - all follicles have formed
oocytes enter meiosis and arrested in prophase 1st meiotic division
some follicular atresia by birth
post-natal ovarian development
many follicles become atretic before puberty
after puberty - hormonal influences stimulate 12-15 follicles for each cycle to develop
only 1 follicle reaches maturity and ovulation
continues until menopause
how many primordial follicles present in the ovary at birth
~2mln
where do the tubular components of the female reproductive system come from
absence of testosterone - degeneration of mesonephros and mesonephric duct
paramesonephric ducts develop to give rise to female genital tract
origin of female genital tract
cranial end of paramesonephric duct becomes associated with ovary
caudal end of paramesonephric ducts (uterovaginal primordium) becomes uterus and superior part of vagina
inferior part of vagina from urogenital sinus
mesonephric duct degenerates
where do the gonads initially form
lumbar region
positional changes occur as development takes place
descent of gonads - testis
wk7 - T10 level, diaphragm undescended
wk12 - level of deep inguinal ring, remains until 7mths
39wks - enters scrotum
descent of gonads - ovaries
wk7 - T10
wk12 - broad ligament
round ligament drawn through inguinal canal to attach to labrum majorum
what causes the descent of the testis
gubernaculum - fibrous cord
shortens and contracts and pulls the testis down through the abdominal wall via inguinal canal into the scrotum
how can intestinal contents pass through the inguinal canal
processus vaginalis not completely closed off
weak point
intestinal contents pass through deep ring and inguinal canal and out through superficial ring
indirect inguinal hernia
what is linked to the descent of the gonads
male - formation of larger inguinal canal, more likely to develop hernias
female - presence of round ligament and its passage through the inguinal canal
gubernaculum in females
pulls the ovary down from original thoracolumbar region to pelvis
once in the pelvic cavity it stops contracting
then degenerates and forms fibrous cord - ovarian ligament and round ligament
why are females less prone to developing inguinal hernias
ovary doesn’t pass through inguinal canal
inguinal canal in females is narrower
3 examples of congenital abnormalities
undescended testis
remnants of mesonephric duct in females e.g. gartner’s cysts
anomalies of paramesonephric duct in female
what is cryptorchidism
abscence of testes in scrotum
4 types of crytptorchidism
undescended
ectopic
retractile testis
absent testes
3 complications of undescended testis
infertility
malignant transformation - germ cell tumours
testicular torsion
locations of undescended testis
abdominal
inguinal
prescrotal (prepubic)
management of undescended testis
orchiopexy
where can remnants of the mesonephric ducts in females occur
epoophoron - near the ovary
paraoophoron - within the broad ligament
Gartner’s cyst - close to vagina
impacts of remnants of the mesonephric ducts
can impact female fertility
anomalies of paramesonephric duct
complete duplication - 2 vagina, 2 uteri with one tube each
bicornuate uterus
septate uterus
arcuate uterus
impacts of anomalies of paramesonephric duct
can all affect implantation of fertilised embryo
