Embryology of the Reproductive System Flashcards
What happens during the process of gastrulation?
bilaminar to trilaminar structure (endo-, meso-, ectoderm)
What 3 sections of the mesoderm exist and how are they arranged?
paraxial - most medial
intermediate
lateral plate - (most lateral)
What part of mesoderm forms the urogenital system?
intermediate
Describe what is meant by cranio-caudal folding?
- Foetus folds from both top and bottom (like a scroll)
- curls into foetal position with yolk sac hanging from middle
What are the 3 segments of the urogenital system which come from the intermediate mesoderm?
Pronephros
Mesonephros
Metanephros
In which direction do the pro-, meso- and metanephros segment?
Cranial to caudal direction
What part of the 3 intermediate mesoderm segments forms the kidney?
metanephros
The mesonephros cannot produce urine as it regresses. TRUE/FALSE?
FALSE
- mesonephros is functional and can produce a small amount of urine
- joins to the cloaca which is responsible for output of developing foetus
The pronephros regresses completely. TRUE/FALSE?
TRUE
At what week does a foetus differentiate into male or female?
WEEK 7
weeks 4-6 undifferentiated gonadal proliferation
Where do the Primordial germs cells stay until migration to the intermediate mesoderm via the dorsal mesentery in weeks 4-6?
In the yolk sac
What do the Primordial germs cells do after migrating in towards the mesonephros?
- Cause proliferation of epithelium => formation of gonadal ridge
- form primitive gonad (Not M/F)
- differentiate into somatic support cells
What two ducts are involved in the formation of genitalia?
Mesonephric (Wolffian) Duct
Paramesonephric (Mullerian) Duct (formed by peritoneum infolding alongside mesonephric duct)
Which duct joins at the bottom just before attaching to the urogenital sinus?
paramesonephric duct
What transcription factor protein is responsible for Male reproductive development after the primitive gonad has been formed?
SRY protein (Sex determining region of Y) - found on short arm of Y chromosome
Describe how the primitive gonad changes to form the male reproductive organs
- Somatic support cells develop into Sertoli cells
- Primary sex cords form medullary cords
- Rete testis connect mesonephric tubules to the seminiferous tubules
- Cortex depletes and thickened layer of connect tissue forms called the tunica albuginea
What are the main functions of sertoli cells?
- stimulate formation of Leydig cells (these secrete testosterone)
- secrete AMH (antimullerian hormone)
=> causes regression of Mullerian (paramesonephric) duct
What does the mesonephric duct form into in a male foetus?
- epididymis
- vas deferens
- seminal vesicles
What hormone stimluates formation of genitalia and how is this hormone made?
Dihydrotestosterone (DHT)
5-alpha-reductase changes testosterone to DHT
What consequences can an AMH mutation cause?
No antimullerian hormone produced
=> female repro tract still develops from paramesonephric duct as it doesn’t regress
What structure is responsible for descending the testis through the inguinal canal?
gubernaculum
Why do the testis descend?
To regulate their temperature and initiate spermatogenesis
What consequence can result from the top of the scrotal cavity being open?
Indirect inguinal hernia
Does the cortex or medulla of the primitive gonad regress if the foetus is differentiating into a female?
Medulla regresses => opposite of males
If medulla regresses there can be no connection to mesonephric duct
What arises from the somatic support cells if a foetus is differentiating into a female?
Granulosa cells surrounding eggs => creating the follicles
What cells are found in females rather than leydig cells?
Thecal cells
No AMH means the paramesonephric duct does not regress in females. What does it form?
Fimbrae form at cranial end of each duct
Rest of duct becomes oviduct
What is the relevance of the epoophoron and the paroophoron?
no function but can form cysts or adenomas
Gartners Cyst is a remnant of what structure in females?
Mesonephric duct
What occurs when the 2 paramesonephric ducts join together and to the cloaca?
- They zip together and form uterus
- myometrium proliferates
- connect to endoderm inferiorly
- vacuolisation to form vaginal cavity and fornix
- hymen closed inferiorly
What fraction of the vaginal cavity is endoderm compared to mesoderm?
Inferior 2/3 endoderm
How may the female repro system develop abnormally?
paramesonephric ducts join urogenital sinus seperately
=> causes 2 uterus’ and 2 vaginas
abnormal zipping of ducts after joining to urogenital sinus
=> bilateral uterus but one vagina
one gonad may not form at all
=> unicornate nucleus
What abnormal development of the female reproductive tract cause a woman to always be infertile?
Cervical atresia
=> no passage for sperm to travel up to fertilise egg
What begins the formation of the external genitalia in both males and females?
Division of cloaca via septum
- forms urogenital sinus and anorectal canal
Describe the undifferentiated formation of external genitalia?
- phallic portion anterior to urogenital sinus bulges forward to form genital tubercle
- infolding of cloaca seperates urethral folds and anal folds
What parts of the undifferentiated external genitalia form the male genitalia?
- genital swelling becomes scrotal swelling
- genital tubercle becomes glans penis
- urethral folds zip up proximal -> distal on ventral aspect of penis
- Ectodermal ingrowth at tip of the glans penis forms the glandular urethra
What abnormality can occur during the zipping of the urethral folds in males?
Hypospadias (opening of urethra too proximal on ventral aspect of penis)
if at level of glans penis - may be caused by ectoderm problem rather than mesoderm
The undifferentiated external changes to what structures in the female?
- genital tubercle = clitoris
- urethral folds - labius minus
- genital swelling - labius majus
