Embryology Flashcards
When does gastrulation happen?
week 3
What is gastrulation?
formation of the trilminar disc - ectoderm, mesoderm and endoderm
invagination of the epiblast cells through the primitive streak to form the definitive endoderm and mesoderm
What are the main groups that the mesoderm is divided into?
partial
intermediate - urogenital system is derived from here
lateral plate
What is the Cloaca?
output that eventually forms the urethra
What is the mesonephric system?
produces urine at a low level and goes alongside the mesonephric duct
What does the metanephric system form?
the kidney
When do the gonads differentiate into male or female?
week 7
How do the genital ridges form?
coelamic epithelium proliferates and thickens
How do the primitive sex cords form?
proliferating epithlium forms somatic support cells which envelope to primordial germ cells
What is the bipotential phase?
occurs up to week 7
development of the genital ducts
What are the two names of the genital ducts?
mesonephric duct (Wollfian) paramesonephric duct (mullarian)
Where do both genital ducts connect?
posterior wall of the urogenital sinus
What is male developement triggered by?
presence of SRY - sex determining region Y
Describe the process of male development?
somatic support cells develop into sertoli cells
primary sex cords form the testis/medullary cords
rete testis connect the mesonephric tubules to form the testis cord
tunica albuginea forms the thickened connective tissue between the coelomic epithelium and testis cord
What is the role of the sertoli cells in male development?
secrete AMH (anti mullarian hormone) which causes degeneration of paramesonephric duct stimulate the gonadal ridge cells to form Leydig cells
What is the role of testosterone?
induces formation of the epididymis, vas deferens and seminal vesicles
What is the role of dihydrotestosterone?
induces male specific external genitalia developement and prostate
What is persistant mullarian syndrome?
due to mutations of AMH or AMH receptor genes
paramesonephric duct fails to regress leading to the formation of a uterus, vagina and uterine tubes, testis in ovary position and external male genitalia
Which verterbal level do the testes originate?
T10
How do the testes descend?
pulled caudally by the gubernoculum
When do male accessory glands form?
week 10
What does the seminal vesicle form from?
outpouching of the mesonephric duct
What do the prostate and bulbourethral glands form from?
endodermal invaginations of the urethra
At what week can you recognise the sex of a baby from a scan?
week 16
What happens to the cloaca to differentiate males and females?
cloaca membrane ruptures and allows free communication
cloacal folds fuse crainally to form the. genital tubercle and caudally to form the urethral folds and anal folds
How is the phallus formed?
elongation of the genital tubercle
How is the penile urethra formed?
urethral folds are pulled to form the urethral groove, then they close to form the penile urethra
How is the foreskin formed?
circular ingrowth of the ectoderm around the periphery of the glands
What is hypospadias?
external urethral opening lies in an abnormal position along the urethral aspect of the penis
How is the clitoris formed?
extension of the genital tubercle
How is the labia minor and major formed?
genital swellings - labia major
urethral folds - labia minor
How is the vestibule that the vagina and urethra open into formed?
urogenital groove
Describe the basics of female development?
germ cells differentiate into oogla then into primary oocytes
somatic support cells differentiate into granulosa cells and surround the primary oocyte, forming primordial follicles in the ovary
What is the role of thecal cells?
stimulate oestrogen
stimulate formation of the female external genitalia and development of the paramesonephric ducts
Where do the paramesonephric ducts open up into?
peritoneal cavity
What do the paramesonephric ducts give rise to?
uterine tubes
uterus
superior vagina
What is a Gartners cyst?
remnant of the mesonephric duct
What are the 3 parts of the paramesonephric duct?
cranial
horizontal
caudal
What does the cranial part of the paramesonephric duct become?
fallopian tube
What does the horizontal part of the paramesonephric duct become?
Fallopian tube
What does the caudal part of the paramesonephric duct become?
uterus
cervis
superior 1/3rd of vagina
What forms the lower 2/3rds of the vagina?
sinovaginal bulbs
