2. Development of the repro. system

Question 1

which factor determines sexual dimorphism (i.e. male vs female gender)

Answer 1

Y chromosome - contains testis-determining SRY gene: under influence of testis-determining factor, male dev. occurs, in its absence, female dev. occurs

Question 2

from which embryrological tissues does the indifferent gonad arise from

Answer 2

1. intermediate mesoderm of urogenital ridge
2. extragonadal primordial germ cells (future sperm/oocytes) - migrate from yolk sac along dorsal mesentery to invade genital ridge in retroperitoneum (week 6) and have inductive influence on dev. of gonad

Question 3

what do the primitive sex cords of the genital ridge develop into in males and females

Answer 3

Males (influence of testis-determining factor):

i. cords proliferate and penetrate deep into gonad medulla to form medullary/testis cords
ii. towards gland hilum, cords break up into network that will give rise to tubules of rete testis
iii. testis cords remain solid until puberty, when they acquire lumen to form SEMINIFEROUS TUBULES

Females (absence of testis-determinening factor):

i. primitive sex cords develop into medullary cords which then degenerate… then form cortical cords which split into isolated cell clusters
ii. clusters proliferate and surround each PGC/oogonium to form a layer of epithelial FOLLICULAR CELLS - form primordial follicles

Question 4

name and describe the 2 pairs of genital ducts possessed initially by both male and female embryo

Answer 4

1. mesonephric (Wolffian) ducts - open onto urogenital sinus on either side of sinus tubercle
2. paramesonephric (Mullerian) ducts - run from adominal cavity, course laterally to MD then cross them ventrally to come into contact with opposite PD at midline. Combined ducts project into posterior wall of UGS at sinus tubercle

Question 5

describe the dev. of male genital ducts - which structures do they give rise to

Answer 5

i. mullerian-inhibiting hormone (from testes Sertoli cells) suppress paramesonephric ducts
ii. testosterone (from testes Leydig cells) support mesonephric duct development
iii. mesonephric ducts develop into:
- efferent ductules
- epididymis
- vas deferens
- seminal vesicles
Migrate with testes as these descend and become part of spermatic cord.

Question 6

describe the dev. of female genital ducts - which structures do they give rise to

Answer 6

i. no production of mullerian-inhibiting hormone, allowing dev. of paramesonephric ducts
ii. no production of testosterone so mesonephric duct degenerates
iii. fusion of 2 paramesonephric ducts at midline creates uterus… ducts pull their pertioneal membrane with them, creates broad ligament of uterus

Question 7

which 2 areas are formed by the uterus and broad ligament dividing the pelvic cavity

Answer 7

1. uterovesical pouch

2. uterorectal pouch

Question 8

what is androgen-insensitivity syndrome

Answer 8

• affects males (Y chromo. + testes) who lack androgen Rs, or whose tissues don’t respond to androgens - no differentiation of male genitalia
• but Ps still have testes and MIH so paramesonephric system is suppressed and uterine tubes/uterus also absent

Question 9

what is the effect of exogenous androgen exposure on female dev.

Answer 9

• exogenous androgen supports mesonephric duct dev. in females (XX chromo)
• but no testes so no MIH, allowing paramesonephric duct dev.

Question 10

describe the dual origin of the vagina

Answer 10

• proximal portion (vaginal fornices) from paramesonephric tube
• distal portion from UGS