PATHWAYS TO MEN AND WOMEN

Question 1

what are the 3 steps to sex determination?

Answer 1

genetic sex which is determined at fertilisation and is based on whether the Y chromosome is present

phenotypic sex which is determined by gonads

secondary sex characteristics which are driven by hormones

Question 2

what does SRY do?

Answer 2

it binds to regions of testis-specific DNA to activate its abilities ti promote testis formation = male

Question 3

what happens when we get mutations in the SRY gene?

Answer 3

disorders of sex development which can have varying effects on phenotype and genotype

Question 4

where do gonads develop from?

Answer 4

bipotential primordia (progenitor cells that can differentiate into testicular or ovarian cells)

Question 5

describe the embryology of forming the indifferent gonads?

Answer 5

primordial germ cells migrate from the yolk sac to the gonadal ridges. the arrival of these cells induces the formation of primitive sex cords.

Question 6

describe the embryology of forming the testes?

Answer 6

SRY gene produces testis-determining factor which causes the proliferation of primitive sex cords and their penetration into the medulla to form testicular cords. some of these differentiate into sertoli cells whilst the rest become incorporated into seminiferous tubules . testicular cords anastamose to form the rete testis

Question 7

describe the embryology of forming the ovaries?

Answer 7

SRY isn’t present so the primitive sex cords extend into the medulla of the gonad, degenerate and form an ovary

Question 8

describe the action of SRY?

Answer 8

expression of SRY-> expression of SOX9 -> expression of PGD2 -> expression of FGF9
SOX9 is also activated by PGD2 and FGF9 so that SOX9 can then inhibit Foxl2 and increase production of AMH

Question 9

what is the function of PGD2?

Answer 9

amplifies the formation of pre-sertoli cells

Question 10

What is the function of FGF9?

Answer 10

attracts mesonephric cells which allows rate testis cords to connect to Wolffian duct

Question 11

What happens when SRY is not expressed?

Answer 11

Foxl2 is not inhibited so we see the expression of Wnt4

Question 12

what is the function of Wnt4?

Answer 12

programmes the formation of granulosa cells

Question 13

What is AMH?

Answer 13

Anti-Mullerian hormone

essential for male development (suppresses the mullerian/paramesonephric ducts as not needed to form fallopian tubes

Question 14

describe the development of the female internal genitalia?

Answer 14

the wolffian duct regresses and the mullerian duct remains to produce the female reproductive tract- caused by no androgens

Question 15

describe the development of the male internal genitalia?

Answer 15

the wolffian duct develops into the epididymis and vas deferens - caused by androgens

Question 16

what is androgen insensitivity syndrome?

Answer 16

androgen is secreted by the testes but the target tissues fail to respond. genotypical male but phenotypically female and infertile.

Question 17

are females the default sex?

Answer 17

yes because only if SRY gene is present does the gonad become a testis and therefore produce sperm.