Embryology Flashcards
What is gastrulation and how & where does this occur?
Formation of the trilaminar disc, cells from the epiblast (ectoderm) invaginate into the area inbetween itself and the hypoblast (endoderm) so third layer (mesoderm) is formed, the cells migrate through the primitive streak
What are the 2 areas in which the mesoderm layer does not develop?
Cranially - oropharyngeal membrane
Caudally - cloacal membrane
How are tubes within tubes created in development? e.g. gut tube inner tube and skin tube outer tube
lateral folding and cranial-caudal folding
What does the urogenital ridge develop from and which part is medial and which lateral?
Intermediate mesoderm
-urinary system lateral and genital system medial
Both excretory ducts of the urogenital fold enter a common cavity. What is this called?
Cloaca
The primordial germs cells (PGC’s) migrate via the dorsal mesentery from yolk sac to where?
To intermediate mesoderm
After the PGCs migrate to urogenital ridge (intermediate mesoderm), coelomic epithelium proliferates and thickens to form what? What will these structures go on to become?
Genital ridges that will go on to become the primitive gonads
What is coelomic epithelium?
Mesothelium that lines the peritoneum
The proliferating epithelial cells forming the genital ridges form continue to proliferate to form what?
Somatic support cells enveloping the PGCs that form the primitive sex cords
What are the two identical pairs of genital ducts?
Mesonephric (Wollfian) duct - eventually form male
Paramesonephric (Mullerian) duct - eventually form female
What marks the ambisexual/bipotential phase of development and what week does sexual differentiation occur?
Genital ducts and indifferent gonads, sexual differentiation occurs from week 7 onwards
What do the primitive gonads form from?
Genital ridges
Female development occurs in the absence of what transcription factor?
SRY - sex determining region of y
The surface epithelium of the ovary gives rise to what?
Cortical cords
PGC’s differentiate into oogonia and then primary oocytes. What develops around these to support them and together what do these form?
Granulosa cells develop around primary oocytes and together they form the primordial follicles in the ovary
What type of cells are thecal cells and what do they produce?
Endocrine cells - produce androgen that will become oestrogen
What do the paramesonephric (Mullerian) ducts become?
Uterus, uterine tubes and superior vagina
What are the 3 parts of the paramesonephric duct (Mullerian)? Which is open into coelomic cavity, which crosses the mesonephric duct and which portion fuses with the paramesonephric duct on the opposite side?
Cranial - opens into coelomic cavity
Horizontal -crosses the mesonephric duct
Caudal - fuses with duct on opposite side
What will happen to the mesonephric ducts in the female?
They will regress
Which part of the paramesonephric duct will give rise to the uterovaginal canal?
Caudal part
How is the vaginal lumen is created by what?
Vacuolisation of the paramesonephric portion of the vagina and the sinuvaginal bulbs
What do the somatic support cells develop into in males?
Mostly into seminiferous tubules but some will differentiate into Sertoli cells
What do the primary sex cords that engulf the PGCs form in the males?
Testis/medullary cords
The tesicular cords anastomose together to form the rete testis. What do the rete testis connect?
Rete testis connect the mesonephric tubules to the testis cords
What does the mesonephric (Wollfian) duct eventually become?
vas deferens (AKA ductus deferens)
A thickened layer of connective tissue forms between the coelomic epithelium and testis cords. What is this called?
Tunica albuginea
How does SRY protein lead to degeneration of paramesonephric duct?
SRY protein stimulates formation of Sertoli cells which secrete AMH (anti-Mullerian hormone) which degenerates paramesonephric duct
What is the role of SRY protein in the formation of the male genitalia and sex organs?
SRY protein stimulates formation of Sertoli cells which stimulate gonadal ridge cells to form Leydig cells. Leydig cells secrete testosterone & dihydrotestosterone (DHT) which form male genitalia and sex organs
Dihydrotestosterone induces formation of epididymis, vas deferens and seminal vesicles and testosterone induces male specific external genitalia development and prostate. True/false?
False - other way around
Testosterone secondary sex organs
DHT external genitalia and prostate
What is Persistent Mullerian Duct Syndrome?
Paramesonephric ducts fail to regress so patients present with uterus, vagina and uterine tubes but will have testes in ovarian location and have male external genitalia
List uterine congenital abnormalities.
- double vagina, double uterus
- bicornate uterus (like two uterus but join at cervix)
- septated uterus
- unicornate uterus
- cervical atresia
Testes originate at ___th thoracic level and are pulled caudally by the ____. Failure to descend of one or both testis is _______.
10th thoracic level
Gubernaculum
Cryptorchidism
Prostate and bulbourethral glands, seminal vesicle glands develop during week 10. What do each develop from?
Prostate and bulbourethral glands are endodermal invaginations from the urethra and the prostate is above the bulbourethral glands. Seminal vesicles develop from mesonephric duct
What does each of these structures become in the female: Genital tubercle Urethral fold Genital swelling Urogenital groove
Genital tubercle - clitoris
Urethral fold - labium minus
Genital swelling - labium majus
Urogenital groove - vagina and urethra
What “zips up” the midline to form the male spongy urethra?
Urethral groove
What tissue grows to form glans penis and prepuce (foreskin)?
Ectodermal ingrowth
An incomplete fusion of the paramesonephric duct
can cause what?
two uteri
THe superior part of the vagina develops from what structure?
paramesonephric duct
