7.2 Development of the female genital system

Question 1

The testes and ovaries develop from the _________________ → medial part of the urogenital ridge (in the dorsal wall of the embryo):
• Germ cells do not appear in the genital ridges until the 6th week of development
• Lateral part of the urogenital ridge is the ______________

Answer 1

genital ridge (intermediate mesoderm);

nephrogenic ridge (develops into kidneys)

Question 2

The genital ducts arise from the paired mesonephric (Wolffian) ducts and paramesonephric (Müllerian) ducts:
• Development and regression of either duct depends on the presence of the __________________ on the Y chromosome (only found in males)

• Epithelium of the genital ridge proliferates and penetrates the underlying mesenchyme to form the primitive sex cords (indifferent gonads)
o In females (no SRY): no Sertoli cells (no ____________) → ___________ development which give rise to _____________ and no Leydig cells (no _____________) → ___________ degenerate

• Primordial germ cells (PGCs) develop in the ________________ → migrate along the dorsal mesentery of hindgut → invade genital ridges
o Inductive influence on the development of the gonad → do not develop if PGCs do not arrive at the genital ridges

Answer 2

SRY (sex determining region Y) gene

Müllerian inhibiting substance;

fallopian tubes, uterus, upper part of vagina

Testosterone;

woffian ducts

wall of the yolk sac;

Question 3

In female embryos (XX sex chromosome complement; no Y chromosome), the primitive sex cords dissociate into irregular clusters:
• Clusters eventually degenerate and are replaced by vascular stroma (ovarian medulla)
• 7th week: surface epithelium gives rise to a second generation of cords (___________) which penetrate underlying mesenchyme but remain close to the surface. The central portion is called the medulla, which mainly contains ___________ while the peripheral part is called the cortex which contains ________________. Medullary cords disappear and cortical cords develops in the ovary.
• 4th month: cords split into isolated cell clusters → each surrounding ≥ 1 PGCs (eventually develop into ________and the surrounding epithelia cells form form ________________)

Answer 3

cortical cords;

the blood vessels;

ovarian follicles;

oogonia ;

follicular cells

Question 4

The gonads develop in the _______________ and descend to their adult anatomical positions (_______ for testes; ________ for ovaries) before birth:

• Female gubernaculum attaches the caudal end of the ovary to the labia majora → leaves behind 2 ligaments by birth

• Ligamentum ovary: Part between the ______________
• Round ligament of uterus: Part between the uterus and labia majora (passes through the _______________ → ___________ → _______________)

Answer 4

abdomen;

scrotum;

pelvis;

ovary and uterus ;

deep inguinal ring;

inguinal canal;

superficial inguinal ring

Question 5

Initially, both male and female embryos have two pairs of genital ducts: mesonephric ducts and paramesonephric ducts.
- In the absence of SRY, the gonad develops into an __________.
Sinceno testosteroneis produced, themost of the _______________ regress in female embryos.
- Since there is alsono Mullarian inhibiting substance (produced by ________),the________________ persistin female embryos

Answer 5

ovary;

mesonephric ducts;

Sertoli cells;

paramesonephric ducts

Question 6

The paramesonephric (Müllerian) ducts eventually give rise to the uterine (Fallopian) tubes, uterus and upper third of the vagina:

• Cranial vertical and horizontal parts of paramesonephric ducts develop into the ____________
• Caudal parts fuse to form the __________ that projects into the dorsal wall of the urogenital sinus.
• Uterine canal gives rise to _________________

Answer 6

uterine tube;

uterine canal;

uterus and upper 1/3 of vagina.

Question 7

Mayer Rokitansky Küster Hauser (MRKH) syndrome: agenesis of the Müllerian system leads to complete absence of the __________________
- 2nd most common cause of primary amenorrhoea (still very rare)

Answer 7

reproductive tract (including upper vagina, uterus, Fallopian tubes)

Question 8

what causes a unicornuate uterus?

Answer 8

Developmental arrest of 1 Müllerian duct

Question 9

what causes a didelphic uterus?

Answer 9

Complete non-fusion of Müllerian ducts (may have 2 vaginas and simultaneous pregnancies)

Question 10

what causes a bicornuate uterus?

Answer 10

Partial/ complete fusion of Müllerian ducts

Question 11

what causes a septate uterus?

Answer 11

Fusion but failure of midline remodelling or resorption of tissue (septum)

Question 12

what causes arcuate uterus?

Answer 12

Least severe; small indent in midline

Question 13

Vagina has dual origin

1. Upper 1/3 of the vagina develops from the ________________
2. Lower 2/3 of the vagina develops from the _________________

Answer 13

uterine canal (paramesonephric ducts);

urogenital sinus (ventral division of the cloaca)

Question 14

Transverse vaginal septum: generally found between the _____________ of the vagina
• Due to failure of degeneration of the ______________
• May be surgically corrected
• Associated with a shortened vagina

Answer 14

upper 1/3 and lower 2/3;

vaginal plate

Question 15

Imperforate hymen: failure of perforation after birth
• Complete obstruction of the vagina
• Commonly diagnosed in adolescence when __________ accumulates in the vagina
• May be surgically incised

Answer 15

menstrual blood

Question 16

Development of the External Genitalia – Indifferent Stage

• Mesenchymal cells proliferates around the cloacal membrane to form a pair of slightly elevated ___________.
• Cranial to the cloacal membrane the folds unite to form the _____________.
• Caudally the folds are subdivided into urethral folds anteriorly and _____________ posteriorly.
• Another pair of elevations, the genital swellings, becomes visible on each side of the urethral folds.
• At the end of the sixth week, however, it is impossible to distinguish between the two sexes.

Answer 16

cloacal folds;

genital tubercle;

anal folds;

Question 17

Development of female external genitilia
- Genital tubercle forms the ___________
- Urethral folds do not fuse develop into the ____________.
Genital swellings enlarge and form the _______________.
- The urogenital groove is open and forms the vestibule

Answer 17

clitoris ;

labia minora;

labia majora

Question 18

Androgen insensitivity (testicular feminisation) syndrome (46XY): Occurs in genetic males → androgen receptor mutation (insensitive to testosterone):
• Presence of SRY: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ regress
• No response to testosterone: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ degenerate → external appearance of normal females (with poorly developed male internal genitalia)

Answer 18

Müllerian ducts;

Wolffian ducts

Question 19

________________: SRY gene mutation → gonadal dysgenesis → phenotypically female (normal external female genitalia, uterus, Fallopian tubes)

Answer 19

Swyer syndrome (46XY)

Question 20

Female pseudo-intersexuality (pseudohermaphroditism) (46XX): Genetic female (ovarian tissue histologically):
• Masculinisation of female external genitalia (enlarged clitoris, partial fusion of labia majora)
• Most commonly caused by ______________ (foetus produces excess androgens)

Answer 20

congenital adrenal hyperplasia

Question 21

Male pseudo-intersexuality (46XY): Genetic male (testicular tissue histologically):
• Underdeveloped male external genitalia
• Most commonly caused by _____________________

Answer 21

inadequate production of testosterone and MIS by foetal testes