Reproductive Tract Embryology Flashcards
What is the default developmental status?
Female
When is genetic sex determined?
At fertilisation
How does the genitalia form?
Internal: from 1 of 2 pairs of genital ducts
External: 1 set of bipotential primordia
Further development occurs at puberty influenced by HPG axis
What affects early male gonad development?
Mullerian Inhibiting Substance (MIS) and testosterone
What are the 3 tissues sources that the gonads develop from?
- Gonadal ridge: intermediate mesoderm at 6 weeks; epithelium penetrates mesenchyme to form primitive sex cords
- Mesodermal epithelium: covers posterior abdominal wall
- Primordial germ cells: migrate from yolk sac around 5-6 weeks to induce development of indifferent gonads
How are males formed?
Expression of the gene Testis Determining Factor (TDF) on Y chromosome influences testicle formation and then testosterone secretion by week 8 influences further sexual differentiation of genitalia
What is Androgen Insensitivity Syndrome (AIS)?
Where a genetic male is made with a normal female appearance because testicles are present usually intra-abdominally and the external genitalia will be a vagina ending as a blind pouch
How does the testes descend?
Along the gubernaculum driven by testicular androgens and processus vaginalis formation guides testicle through inguinal canal and into scrotum - tunica vaginalis remains as a 2-layered fold on peritoneum surrounding the testicle called the tunica vaginalis
How do the ovaries descend?
Along the gubernaculum but it only permits descent into the pelvic cavity at the broad ligament (peritoneum covering uterus and uterine tubes), not through the inguinal canal
What can happen if there is maldescent of the testes?
Most appear by 3 months post-birth and you can watch/wait or surgically correct:
1. Cryptorchidism: testicle has not fully descend and gets stuck (commonly in inguinal canal)
2. Ectopic: testicle traverses inguinal canal and then does not end up in the scrotum
= increases risk of testicular cancer
What does the female gubernaculum form?
Attaches to uterus and forms:
- Ligament of ovary (ovary to uterus)
- Round ligament of uterus (uterus to labia majora)
What are the 2 pairs of genital ducts that contribute to the internal reproductive systems?
- Mesonephric (Wolffian) = male (forms epididymis, ductus deferens, seminal vesicle, ejaculatory duct and partly ureters)
- Paramesonephric (Mullerian) = female (forms uterine tubes, uterus and upper vagina)
Where does all the female reproductive tract form?
Urogenital sinus - some develops bladder and some becomes the vagina
What happens to the mesonephric duct?
In males: testosterone productive drives its development at week 8
Females: degenerates spontaneously - remnants can remain around the ovary (epophoron), lateral to uterus or vaginal wall (Gartner’s duct) which can form cysts
What happens to the paramesonephric duct?
Males: Anti-Mullerian hormone production by Sertoli cells causes paramesonephric duct regression at week 6/7 - small remnant called the appendix of the testicle can remain just above the testicle which can be seen on US imaging which can cause cysts but is mostly quiescent
Females: persists and develops because there is a lack of testosterone and anti-Mullerian hormone
How does the paramesonephric duct form?
Via invagination of the coelomic epithelium (future peritoneum) similar to neural tube formation where the proximal uterine tube stays open and communicates with the peritoneal cavity so ovulation takes place here where the egg is - this is why ectopic pregnancies can implant anywhere in the peritoneum e.g. under liver or GI tract. It moves to the midline and fuses to form the uterus pulling with it a fold of peritoneum which becomes the broad ligament which gives it nerve/blood supply.
What can be the result of a uterine/vaginal malformation?
Primary amenorrhoea
Subfertility
Problematic pregnancy
What is the purpose of the urorectal septum?
Divides the cloaca into the urogenital sinus and rectum - eventually becomes the perineal body
What is the perineal body?
Point of union between pelvic floor and perineal membrane important for integrity of pelvic floor providing support to the posterior vaginal wall and being an attachment point for the anal sphincter - more of a deficit in support in FEMALES then males
What is a maldevelopment of the anorectal region called?
Imperforate anus - requires surgical correction
What does the vagina develop from?
The uterovaginal primordium makes the uterus and upper vaginal canal and the sinovaginal bulb of the urogenital sinus - the point of meeting of these 2 tissues forms the vaginal plate which must cannulise and open up
What is just beyond the sinovaginal bulb?
Thin membrane called the hymen which should disappear in early life
What happens if the solid vaginal plate fails to canalise?
Vaginal atresia: vagina is not open as plate does not cannulise
Transverse vaginal septa: septation in the vagina which can be high, middle or low
What can happen if the hymen does not rupture in early life? What can you do about it?
Variations in hymen perforation e.g. imperforate, annular, septate, cribriform etc. which generally tend to present around time of first period and can cause severe pain so must be surgically presented
What are some key embryological features and what do they form in the male/female?
- Urogenital/urethral fold: spongy urethra (male) or labia minora (female)
- Labioscrotal swelling: scrotum (male) and labia majora (female)
- Genital tubercle: penile glans and erectile tissue (male) and clitoris (female)
Where does joining of the genital tissue occur?
Where the genital/labioscrotal tissue swells
What is the line of fusion called in the male?
Midline raphe
What can go wrong with the male external genitalia?
The male urethra can be malformed and can open onto the dorsal or ventral penis (anatomical position) leading to hypospadiasis commonly near tip on the ventral side but can also occur on the dorsal side being called a epispadias which is much rarer
What should you be concerned about if a male has a epispadias?
Other midline birth defects e.g. cardiac, pelvic girdle or bladder may be protruding from abdominal wall
