Embryo: reproductive system Flashcards
When does reproductive system development begin?
Week 4
When do the PGCs arrive at the primitive gonads?
Week 5
When do the PGCs invade genital ridges?
Week 6
When are PGCs distinguishable male/female?
Weke 7
Urogenital system is functionally divided into the ____ & _____?
Urinary System
Reproductive System
What is the urogenital system developed from?
Mesodermal ridge (of intermediate mesoderm)
Intermediate mesoderm swells to form ____
Urogenital ridge
Urogenital ridge swells into the ____ cavity forming two ridges. What are those two cavities? Which is medial/lateral?
Intracoelomic cavity
Medial ridge = genital ridge
lateral ridge = nephrogenic cord/ridge
What does the genital ridge derive from?
the medial ridge of the urogenital ridge
What does the genital ridge give rise to?
the reproductive system
What does the nephrogenic cord derive from?
the lateral ridge of the genital ridge
What does the nephrogenic cord give rise to?
the urinary system
Week 4, PGC migrate from ___ along ___ to arrive at ___
migrate from wall of yolk sac
along dorsal mesentery of hindgut
to arrive at the primitive gonads
When do the PGCs arrive at the primitive gonads?
week 5
When do the PGCs invade the genital ridge?
week 6
What happens if the PGCs fail to reach the genital ridges? Why is this?
Then the gonads do not develop.
This is because the PGCs have an inductive influence on gonadal development
When is the sex of am embryo genetically determined?
At time of fertilization
When do the gonads of am embryo acquire morphological characteristics?
Week 7
What are the genital ridges formed by?
proliferation of epithelium and condensation of underlying mesenchyme
Genital ridges aka ____
gonadal ridges
What are genital ridges morphologically?
A pair of longitudinal ridges
What are primitive sex cords formed from?
epithelial cells of genital ridge penetrate underlying mesenchyme to form primitive sex cords
What are primitive sex cords morphologically?
irregularly shaped cords
At the primitive sex cord stage, are the gonads differentiated or indifferent?
PRIMITIVE SEX CORD STAGE IS INDIFFERENT GONADS
What are the two pairs of genital ducts formed in development?
Mesonephric (Wolffian) duct
Paramesonpehric (Mullerian) duct
The mesonephric ducts open into the ____ one either side of the ___
The mesonephric duct opens into the urogenital sinus on either side of the sinus tubercle
Paramesonephric ducts run ____ to mesonephric duct and pass it ___
paramesonephric duct runs lateral to mesoneophric duct and passes over it ventrally
What happens to the paramesonephric ducts at the midline?
They come in close proximity to the contralateral paramesonephric duct
What forms the sinus tubercle?
The caudal tip of the combined paramesphric ducts project into the posterior wall of the urogenital sinus causing sinus tubercle
What does the Y chromosome house?
the SRY Gene
What does the SRY gene do?
encodes for TDF (testes determining factor) which leads to testes development
What happens to primitive sex cords under influence of SRY gene?
primitive sex cords continue to proliferate and penetrate deep into medulla to form testes (medullary) cords
How are the testes (medullary) cords formed?
primitive sex cords proliferate and penetrate due to influence of SRY gene forming testes cords
What happens to the testic cord near the hilum of the testis?
Testic cord breaks up into network of tiny cell strands and gives rise to tubules of RETE TESTIS
What are the rete testes?
At the hlium of the testis, the testis cord breaks up into tiny cells = RETE TESTIS
What is the tunica albuginea?
dense layer of fibrous connective tissue that separates the testis cords from surface epithelium
What does the tunica albuginea separate?
the testis cords from surface epithelium
@ month 4, testis cords become ___ shaped and continuous with ____.
Horseshoe shaped and continuous with rete testis
When do the testis become horseshoe shaped and continuous with rete testis?
month 4
What is the horseshoe testis cord composed of?
PGCs and Sertoli Cells (sustentacular cells)
What are sertoli cells and where are they? Sertoli cells aka ____
Sertoli cells aka sustentacular cells
They are supporting cells derived from testis surface epithelium
They are in the horeshoe shaped testis cord
Leydig cells aka ____
interstitial cells
Where are leydig cells derived from?
Leydig cells are derived from the mesenchyme of gonadal ridge
Where do leydig cells lie?
between the testis cords (INTERESTITIAL cells)
What do the leydig cells produce? when do they produce it?
Week 8: produce testosterone
testis able to influence sexual differentiation of genital ducts and external genitalia
Are the testis cords solid or hollow?
Testis cords are solid until puberty
What happens to testis cords during puberty? What is formed?
Testis cords acquire a lumen and form seminiferous tubules
Seminiferous tubules join the rete testis which enter ____
ductili efferentes (efferent ductules)
What do the ductuli efferentes (efferent ductules) do?
They link the rete testes and mesonephric (wolffian duct)
What does the mesonephric (wolffian) duct give rise to in males?
main genital ducts
- efferent ductules
- epididymas
- vas deferens (ductus deferens)
- seminal vesicle
- ejaculatory duct
What do sertoli cells produce?
Anti-mullerian hormone (AMH) / Mullerian inhibiting substance (MIS)
causing paramesonephric ducts to degenerate
Where do the paramesonephric ducts remain present in males?
paramesonephric ducts degenerate everywhere in males except small cranial portion for the APPENDIX TESTIS
Do testes develop retroperitoneal or intraperitoneal?
retroperitoneal
Trace the path of testes descent
Develop in abdominal region
move caudally and pass through abdominal wall through inguinal canal to reach scrotum
What is the gubernaculum in male reproductive development?
condensation of mesenchyme extending from the caudal pole of testis
anchors testis to floor of scrotum and assists in it’s descent into scrotum
When does the testes descent begin? When do the testes pass through the inguinal canal?
Month 3 testes descent begins
Month 7 testes pass through inguinal canal (with help from gubernaculum)
What is the processus vaginalis?
an evagination of peritoneum from abdominal cavity that follows the course of the gubernaculum into the scrotal swellings
What are the 4 layers that cover testes through it’s descent and where they derive from?
- VISCERAL/PARIETAL TUNICA VAGINALIS from processus vaginalis
- INTERNAL SPERMATIC FASCIA from transversalis fascia
- CREMASTERIC FASCIA AND MUSCLE from internal abdominal oblique muscle
- EXTERNAL FASCIA from external oblique muscle
Which abdominal muscle does not contribute to the testes coverings while descending?
Transversus abdominis muscle
What happens to primitive sex cells in ovary development?
They dissociate into irregular cell clusters that contain groups of PGCs which occupy medullary part of ovary
What happens to surface epithelium in female development?
Surface epithelium continues to proliferate until week 7 when it gives rise to a second generation of cords - CORTICAL CORDS
What are cortical cords?
Female surface epithelium proliferates to give rise to these.
What do cortical cords penetrate?
underlying mesenchume, they remain close to the surface
How do cortical cords surround each oogonium? When?
Month 3, cords split into isolated cell clusters which proliferate and surround each oognoium with an epithelial layer
FORMING A FOLLICULAR CELL
what is a follicular cell?
an epithelial layer of cell clusters from cortical cords surrounding an oogonium
What forms a primordial follicle?
follicular cells + oogonium = primordial follicle
What influence does the presence of estrogen (and absence of testosterone) have on the genital ducts?
- paramesonephric (mullerian) ducts develop into female genital ducts
- mesonephric ducts degenerate
What are the 3 initial portions recognizable in the paramesonephric duct in female development?
- Cranial vertical portion: opens to abdominal cavity
- Horizontal part: crosses mesonephric duct ventrally
- Caudal vertical part: fuses with counterpart on opposite side
What does the paramesonephric duct give rise to?
Uterine tube and uterine canal (corpus of uterus aka corpus uteri, cervix, upper portion of vagina)
What are the 3 components of the uterine canal?
- corpus uterus (corpus uteri)
- cervix
- upper portion of vagina
Fused caudal ends of paramesonephric ducts contact the __ wall of the _____ inducing a thickening.
posterior wall of urogenital sinus
How is the sinus tubercle formed?
fused paramesonephric caudal ends contact posterior wall of urogenital sinus and induce a thickening
What are the sinovaginal bulbs grown from?
Two solid evaginations grow out from sinus
What do the sinovaginal bulbs form?
they proliferate and form a solid vaginal plate
What is the purpose for proliferation of the vaginal plate CRANIALLY?
to increase the distance between the uterus and the urogenital sinus
What is the vaginal plate formed from?
The proliferation of the sinovaginal bulbs
When is the vaginal outgrowth canalized?
month 5
What are the vaginal fornices? What is their origin?
paramesonephric origin
they are wing like expantions at the caudal ends of the uterus
What are the two origins of the vagina?
Upper portion is derived from the uterine canal
Lower portion is derived from the urogenital sinus
What is the purpose of the hymen during development?
thin tissue plate that separates the urogenital sinus from the lumen of the vagina
Where do ovaries originally develop?
In high abdomen. Must descend and settle just below rim of true pelvis.
What are the two genital ligaments that help with the descent of ovaries?
Cranial genital ligament
caudal genital ligament
What does the cranial genital ligament form?
suspensory ligament of the ovary (contains ovarian vasculature)
What does the caudal genital ligament form?
ligament of the ovary proper (aka round ligament of the ovary)
and round ligament of the uterus (which continues through the inguinal canal)
What does the caudal genital ligament anchor inferiorly with?
the labia majora
Walk through the indifferent stage of external genitalia development
mesenchymal cells from prim. streak migrate around cloacal membrane to form CLOACAL FOLDS
cranial to cloacal membarne = GENITAL TUBERCLE
caudally, folds subdivided into URETHRA FOLDS (anterior), ANAL FOLDS (posterior)
lateral to urethral folds a pair of elevations become visible on each side= GENITAL SWELLINGS (scrotal swellings and labia majora)
What happens to the genital tubercle in male external genitalia development? What is formed?
rapid elongation of genital tubercle to form PHALLUS
During genital tubercle elongation in males, the phallus pulls __ along with it, forming ____.
During genital tubercle elongation, phallus pulls the URETHRAL FOLDS forward forming the walls of the URETHRAL GROOVE
How does the urethral groove elongate? It elongates up until what point?
(in males)
Urethral groove extends along caudal aspect of elongated phallus up until where the distal part of the phallus is.
What part of the phallus does the urethral groove not reach? Why?
(in males)
the most distal part
because that is where the glands are
What is the urethral plate in terms of male external genitalia development? What does it originate from?
urethral plate is the epithelial lining of the urethral groove
originates from endoderm
In male external genitalia development, the two urethral folds close over the ___ forming the ____
fold over the URETHRAL PLATE to form the PENILE URETHRA
does not extend to tip of phallus
When is the most distal portion of the urethra formed?
male external genitalia development
month 4
How does the distal portion of the urethra fold?
male external genitalia development
ectodermal cells from tip of glands penetrate inward
form short epithelial cord
cord later obtains a lumen to become the EXTERNAL URETHRAL MEATUS
What do genital swellings become in male external genitalia development?
In which direction to they move while growing? Which region do they arise from?
Each genital swelling becomes a scrotal swellings
They move CAUDALLY and arise in the inguinal region
What are the two scrotal swellings separated by?
scrotal septum
line of fusion of scrotal swellings
What hormone stimulates development of external genitalia of females?
estrogen(s)
How does the genital tubercle elongate in female external genitalia formation? What does it become?
Elongates only slightly
forms clitorus
What happens to the urethral folds in female external genitalia development? What does it become?
They do NOT fuse
they develop into the labia minora
What happens to the urogenital groove in female external genitalia formation? What does it become?
urogenital groove is OPEN
forms the vestibule of the vagina
