Reproductive Embryology Flashcards
How can reproductive development be divided?
The gonads
Internal genitalia
External genitalia
What is the first stage of gonad development?
Indifferent stage
Where does gonad development begin?
Genital ridges - longitudinal ridges derived from intermediate mesoderm and overlying epitheloum
When does reproductive system begin to develop?
Week 4 = germ cell migration
Week 6 = development
What happens during the indifferent stage of gonad development?
Germ cells migrate from endoderm lining of yolk sac to genital ridges
Simultaneously the genital ridges proliferate to form primitive sex cords
How does the indifferent gonad develop into a testis?
Male = XY chromosomes = SRY gene
SRY gene stimulates development of testis cords
Part of testis cord breaks off to form rete testis
Rest of testis cord contains
- germ cells
- sertoli cells
Between testis cords = leydig cells - produce testosterone
What are leydig cells derived from?
Intermediate mesoderm
When do leydig cells start to produce testosterone?
Week 8
How does the indifferent gonad develop into ovaires?
No Y chromosone = no SRY gene
Primitive sex cords degenerate
Instead gonad epithelium proliferates = cortical cords
What happens to the cortical cords?
Break up into clusters and surround oogonium to form primordial follicle
What is the indifferent stage of internal genitalia development?
Production of
- Mesonephric ducts
- Paramesonephric ducts
Both end at the cloaca
What is the mesonephric duct also known as?
Wolffian duct
What is the paramesonephric duct known as?
Mullerian duct
How do the ducts develop in a male?
Testosterone
- development of mesonephric ducts
Sertoli cells produce anti-mullerian hormone = degeneration of paramesonephric ducts
What is derived from the mesonephric duct?
Efferent ductules
Epididymis
Vas deferns
Seminal vesicles
How do the ducts develop in a female?
No testosterone
- degeneration of mesonephric ducts
Absence of anti-mullerian hormone
- development of paramesonephric ducts
What is the remnant of mesonephric ducts in females called?
Gartner’s duct
What is derived from the paramesophric ducts?
Cranial = fallopian tubes
Caudal
- uterus
- cervix
- upper 1/3 vagina
What forms the lower 2/3 vagina?
Sinovaginal bulbs - derived from pelvic part of urogenital sinus
What happens in the indifferent stage of external genitalia development?
Mesenchymal cells from primitive streak migrate to cloacal membrane to form pair of cloacal fols
Cranially - fuse to form genital tubercle
Caudally - divide into urethral and anal folds
Genital swellings develop either side of urethral folds
How does the indifferent genitalia develop into male external genitalia?
DHT from testes driven
Rapid elongation of genital tubercle = phallus
Urethral folds pulled to form urethral groove - folds close to form urethra
Genital swellings = scrotum
How does the indifferent genitalia develop into female external genitalia?
Driven by oestrogen
Genital tubercle = clitoris
Urethral folds and genital swellings do not fuse - form labia
Urogenital groove - forms vestibule for urethral + vaginal openings
How do the testes descend?
Tethered to scrotum by gubernaculum
Week 28 - pass through inguinal canal
Week 33 - reach scrotum
Keep original blood supply
How do the ovaries descend?
Tethered to labia by gubernaculum
Pulled down but growth of uterus prevents too much descent
