Aug30 M2-Embryology_Urogenital_Sinus_and_External Genitalia Flashcards
UGS is what type of cells
endoderm
what is imp and related to UGS
mesenchyme around it
- IMPORTANT for differentiation of parts I, II, III
- produces enzymes that convert testo and this influences how male external genitalia form
bipotential pelvic viscera are made of what
- UGS
- urorectal septum
- anal canal
location of the genital tubercle
on the pubic bone level
what portion I of the UGS forms in the male
bladder
what portion I of the UGS forms in the female
bladder
what portion II (pelvic portion) of the UGS forms in the male
- prostatic urethra
- prostatic epithelium
- deep perineal pouch with membranous urethra and bulbourethral (Cowper’s) glands
what portion III (definitive portion) of the UGS forms in the male
penile urethra
what portion II (pelvic portion) of the UGS forms in the female
- membranous urethra
- lower vagina (upper came from PMD Hox13 gene)
what portion III (definitive portion) of the UGS forms in the female
- vestibule
- greater vestibular glands (Batholin’s glands)
two ducts entering the UGS
- MD + ureter (which comes from the MD)
2. PMD
origin of the ureter
MD
where MD (+ureter) and PMD enter in the UGS
in the pelvic portion (II)
urorectal septum is what type of tissue
mesenchyme. separates UGS from the anorectal canal
2 swellings of the external genitalia
- urogenital fold
- labio-scrotal fold
- also have genital tubercle on outside on top of these*
where ureters enter the bladder
in the back, to form the trigone
where the bladder ends
in the allantois
chemical reaction needed for normal diff of male UGS and external genitalia
testo conversion to DHT by 5 alpha reductase
what the mesonephric duct entering the pelvic portion of UGS (II) will form in the male
- vas deferens
- seminal vesicles
- ejaculatory duct
of MD and PMD (bipotential state still), which will remain and enter the prostatic urethra
both
- MD really
- PMD degenerates and tubercle remains attached to the prostatic urethra (IS CALLED THE UTRICLE)
what express the hox genes for PMD diff in the female
the mesenchyme around the PMD
how is the prostate formed in the male
- Hox13 is expressed in the mesenchyme around the prostatic epithelium (from UGS II, which is endoderm)
- Hox13 induces a segment of the prostatic urethra (from UGS II, which is endoderm) to form approx 20 pairs of endodermal buds (endoderm)
- these buds grow out of the urethra to form the prostate and prostate stem cells. They interact with the prostatic urethra
narrowest portion of the urethra
membranous urethra (from pelvic region (II) of UGS)
origin of the bulbourethral glands
membranous urethra
what is present in the tip of the bladder in the midline
urachus, derived from the allantois
after allantois and then urachus, what does the projection of the bladder to the umbilicus become
median umbilical ligament
what is found below the umbilicus in the embryo (in a vertical line)
pubic bone, and just below it, genital tubercle
initial place where PGCs are found
allantois
where PGCs go after allantois
- bladder
- hindgut
- gonads* (UGR)
what has to happen to the UGR after the PGCs reach the gonads
it has to degenerate and it forms the median umbilical ligament going all the way to the umbilicus
anomalies related to abnormal closing of the peritoneum over the bladder (related to median umbilical ligament)
- fistulas
- sinus ejection
- urachal cysts
umbilical fistula is what
improper closing of the urachus (peritoneum over the bladder) to form a median umbilical ligament so there’s an opening form the bladder all the way up to the umbilicus
sinus ejection is what
instead of an umbilical fistula, a big depression is formed instead of the normal median umbilical ligament
urachal cyst is what
- proper forming of the median umb ligament but improper closing of one portion (like mid portion)
- a little sac is formed, lined by endoderm (is a urachal cyst)
what is the Muellerian tubercle
inferior tip of the PMD
in both M and F, both MD and PMD reach the urogenital sinus. what happens in F when Muellerian tubercle touches the UGS
- you get the formation of a bifid sinovaginal bulb (SVB) (ENDODERM)
- the SB grows out of the contact between Muellerian tubercle and UGS
- it keeps growing into a mesoderm (or paramesoderm) (mesoderm of PMD) called the utero vaginal primordium (superoposteriorly to the bladder)
what express Lim-1 + what’s the point
- the PMD
- is necessary for formation of uterus, cervix and upper third of vagina
two sources of the vagina
- upper = PMD mesoderm
- lower = pelvic portion (II) of the UGS
steps to complete formation of vagina and uterus
- formation of vagina from its two sources and the 2 SVBs push the uterus up
- recanalization (apoptosis) in both mesodermal portion of the vagina (2 projections so 2 recanalization, comes from mesoderm of PMD formed by SVB) and the endodermal portion of the vagina (pelvic portion more anterior)
what’s a septate vagina
- abnormal recanalization of the two mesoderm projections
- get a double vagina (septum in the middle)
normal vagina histo
stratified squamous epithelium
why was there an increased risk of adenosis (benign) or adenoCA (cancer) of the vagina in children of mothers who took DES
- bc it disrupted hox genes for vaginal formation (estrogens affect hox genes)
- the upper third of the vagina becomes glandular like the cervix instead of strat squamous epith (like normal)
- this glandular epith can become adenosis or adenoCA
cause of the vaginal septum
2 SVBs grew and apoptosis worked EXCEPT for their center, which didn’t degenerate so get septate vagina
septate vagina assoc with what anomaly
bicornuate uterus (caused by failure of PMD fusion)
what is around the external genitalia
mesenchyme that has 5 alpha hydroxy testo enzyme which makes testo into DHT
effect of mesenchyme with 5 alpha reductase around the external genitalia (what’s the effect of DHT)
- causes the urogenital folds to grow
- the genital tubercle enlarges and eventually the whole tube closes (tube formed by urogenital folds on both sides and genital tubercle at the tip. all their mesenchyme is actively proliferating)
- the labioscrotal fold enlarges and is displaced downwards
- the endodermal plate of the UGS III (UGS membrane) between the urogenital folds ruptures.
why does the UGS III membrane break between the urogenital folds
to allow the urethra to use this path and close there. (it creates the future lumen of the urethra)
end function of the labioscrotal fold
grows downwards and the testes will go there and it will be the area where they grow
origin of the penis
- genital tubercle
- urogenital folds (corpus spongiosum and corpora cavernosa)
1. folds and mesenchyme grow towards the tubercle and continue that way
2. folds fuse in the middle of the perineal region (starting from near the perineal body and going anteriorly)
3. this closing is what closes the penile urethra
where do the urogenital folds forming the penis stop fusing and end
in the ectoderm of the glans, where the glans meets the endodermal penile urethra
hypospadia (1 in 300 births) definition
anomaly of the urogenital folds closing anywhere along the axis of closure, causing an opening of the penile urethra on the ventral aspect of the penis
hypospadias most commonly where
in region near the gland (glans)
epispadias (1 in 30 000 births) def
anomaly of the urogenital folds closing anywhere along the axis of closure, causing an opening of the penile urethra on the DORSAL aspect of the penis
origin of the genital tubercle
two little tubercles on each side
cause of epispadias
genital tubercle went to the bottom (ventrally) instead of going to the top. so as you go towards the end of the penis, the penile urethra reaches an opening on the dorsal aspect
why the female external genitalia grows differently
females have no testo so even though the mesenchyme around the external genitalia has 5 alpha reductase, no DHT is made
dev of female external genitalia
- UG folds grow up and are bent over
- the UGS III membrane opens and remains open to form the vestibule (doesn’t close bc of UGFs as in the male)
external genitalia of female and origin
- labia minora = urogenital folds
- labia majora = labioscrotal fold
- genital tubercle = clitoris and prepuce of the clitoris
what is pseudohermaphroditism
in a female newborn, development of male-like external genitalia because of congenital adrenal hyperplasia where a lot of androgens are produced
labioscrotal folds will fuse (As when the scrotum is formed)
what happens in the male if there is no 5 alpha reductase in the mesenchyme surrounding the external genitalia
- genital tubercle underdevelopped
- UG and LS folds stay open, don’t fuse
- LSFs are very small
- the testicules may not come down
- get female-like external genitalia
how the UGR is formed
-inside the paraxial plate mesoderm, the coelomic epithelium forms the coelum (which is coelomic epith)
-this will form the whole body cavities
-it will line the UGR
the primary sex cords in the male (which form Sertoli cells, PGCs and rete beginning) and in the female (to form follicular cells and PGCs)
-this UGR made of coelomic epith will make AMH and testo
functions of the coelomic epith lining the UGR
- lines the primary sex cords in the male (to form Sertoli cells, PGCs and rete beginning) and in the female (to form follicular cells and PGCs)
- this UGR made of coelomic epith will make AMH and testo
- the UGR made of coelomic epith also makes NCCs which develop the adrenal cortex, for hormone production
clinical significance of coelomic epith
- lines the whole peritoneal cavity
- slow turnover rate so involved in many neoplasms
- mesothelioma is a very serious neoplasm of the pleural cavity
- coelomic epith also lines the ovaries (ovarian CA implications)
- also involved in endometriosis since lines it (bc the coelomic epith is what forms the PMD which forms the endometrium so endometriosis is an ectopic endometrial formation)
