Reproductive Tract Embryology

Question 1

What is the default developmental status?

Answer 1

Female

Question 2

When is genetic sex determined?

Answer 2

At fertilisation

Question 3

How does the genitalia form?

Answer 3

Internal: from 1 of 2 pairs of genital ducts
External: 1 set of bipotential primordia

Further development occurs at puberty influenced by HPG axis

Question 4

What affects early male gonad development?

Answer 4

Mullerian Inhibiting Substance (MIS) and testosterone

Question 5

What are the 3 tissues sources that the gonads develop from?

Answer 5

1. Gonadal ridge: intermediate mesoderm at 6 weeks; epithelium penetrates mesenchyme to form primitive sex cords
2. Mesodermal epithelium: covers posterior abdominal wall
3. Primordial germ cells: migrate from yolk sac around 5-6 weeks to induce development of indifferent gonads

Question 6

How are males formed?

Answer 6

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

Question 7

What is Androgen Insensitivity Syndrome (AIS)?

Answer 7

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

Question 8

How does the testes descend?

Answer 8

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

Question 9

How do the ovaries descend?

Answer 9

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

Question 10

What can happen if there is maldescent of the testes?

Answer 10

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

Question 11

What does the female gubernaculum form?

Answer 11

Attaches to uterus and forms:

1. Ligament of ovary (ovary to uterus)
2. Round ligament of uterus (uterus to labia majora)

Question 12

What are the 2 pairs of genital ducts that contribute to the internal reproductive systems?

Answer 12

1. Mesonephric (Wolffian) = male (forms epididymis, ductus deferens, seminal vesicle, ejaculatory duct and partly ureters)
2. Paramesonephric (Mullerian) = female (forms uterine tubes, uterus and upper vagina)

Question 13

Where does all the female reproductive tract form?

Answer 13

Urogenital sinus - some develops bladder and some becomes the vagina

Question 14

What happens to the mesonephric duct?

Answer 14

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

Question 15

What happens to the paramesonephric duct?

Answer 15

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

Question 16

How does the paramesonephric duct form?

Answer 16

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.

Question 17

What can be the result of a uterine/vaginal malformation?

Answer 17

Primary amenorrhoea
Subfertility
Problematic pregnancy

Question 18

What is the purpose of the urorectal septum?

Answer 18

Divides the cloaca into the urogenital sinus and rectum - eventually becomes the perineal body

Question 19

What is the perineal body?

Answer 19

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

Question 20

What is a maldevelopment of the anorectal region called?

Answer 20

Imperforate anus - requires surgical correction

Question 21

What does the vagina develop from?

Answer 21

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

Question 22

What is just beyond the sinovaginal bulb?

Answer 22

Thin membrane called the hymen which should disappear in early life

Question 23

What happens if the solid vaginal plate fails to canalise?

Answer 23

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

Question 24

What can happen if the hymen does not rupture in early life? What can you do about it?

Answer 24

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

Question 25

What are some key embryological features and what do they form in the male/female?

Answer 25

1. Urogenital/urethral fold: spongy urethra (male) or labia minora (female)
2. Labioscrotal swelling: scrotum (male) and labia majora (female)
3. Genital tubercle: penile glans and erectile tissue (male) and clitoris (female)

Question 26

Where does joining of the genital tissue occur?

Answer 26

Where the genital/labioscrotal tissue swells

Question 27

What is the line of fusion called in the male?

Answer 27

Midline raphe

Question 28

What can go wrong with the male external genitalia?

Answer 28

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

Question 29

What should you be concerned about if a male has a epispadias?

Answer 29

Other midline birth defects e.g. cardiac, pelvic girdle or bladder may be protruding from abdominal wall