L18

Question 1

what determines sex?

Answer 1

the chromosomal complement of sperm

Question 2

6 weeks

Answer 2

the foetus has a biopotential primordium and rudimentary reproductive tracts

Question 3

define a bipotential primordium

Answer 3

an embryonic structure with the capacity to develop into either a male (testis) or female (ovary) gonad

Question 4

how does the bipotential primordium develop if the Y chromosome is present?

Answer 4

testis
Wolffian duct -> epididymis, vas deferens, seminal vesicle

Question 5

how does the bipotential primordium develop if the Y chromosome is absent?

Answer 5

ovary
Mullerian duct -> fallopian tube, uterus, upper vagina

Question 6

development of structures in XX embryos

Answer 6

10 weeks:
1. gonadal cortex becomes ovary in the absence of SRY protein and under the influence of female-specific genes
2. absence of testosterone causes Wolffian duct to degenerate
at birth:
3. absence of anti-Mullerian hormone (AMH) allows the Mullein duct to become the fallopian tube, uterus, and upper part of the vagina

Question 7

development of structures in XY embryos

Answer 7

10 weeks:
1. SRY protein in male embryo directs the medulla of the bipotential gonad to develop into testis
2. Anti-Mullerian hormone from testis causes the Müllerian ducts to disappear
at birth:
3. testosterone from testis converts Wolffian duct into seminal vesicle, vas deferent, and epididymis. DHT controls prostate development

Question 8

what is so special about the Y chromosome?

Answer 8

has SRY gene that promotes testes development

Question 9

how does SRY promotes testes development

Answer 9

encodes TDF (testes-determining factor) a transcription factor

Question 10

describe the genetic mechanism through which the testes form

Answer 10

1. SF1 is expressed in the bipotential primordium and acts together with SRY to activate the transcription of the SOX9 gene
2. SOX9 activates transcription of FGF9, AMH, DHH, SF1
3. this leads to development of Sertoli cells (AMH) and testes, development of Leydig cells (testosterone), and repression of female structures (via AMH)

Question 11

SF1 stands for

Answer 11

steroidogenic factor 1 (transcription factor)

Question 12

high levels of SOX9 in males suppress

Answer 12

β-catenin

Question 13

β-catenin in females suppresses

Answer 13

SOX9

Question 14

how does SOX9 initiate Sertoli cell differentiation?

Answer 14

• growth factors cause the proliferation of Sertoli precursors
• Sertoli precursors organise around clusters of germ cells

Question 15

what cellular events downstream of SOX9 help to organise testis structure?

Answer 15

proliferation, migration, organisation, vascularisation, Leydig cell differentiation

Question 16

label a flow chart of how hormones help to regulate structural differentiation in males

Question 17

label the localisation of testosterone and DHT in common XY structures

Question 18

hormones in common XX structures

Answer 18

• β-catenin suppresses SOX9 expression
• no AMH or testosterone
• estrogens and estradiol

Question 19

What causes variations in sex development due to atypical hormone levels or action in XY and XX individuals?

Answer 19

XY – atypical androgen synthesis (e.g., 5-a-reductase) or action
XX - excessive exposure to androgens during early gestation

Question 20

XY individual with androgen insensitivity

Answer 20

• testes (undescended)
• vagina (lower portion, closed end)
• androgens high, LH high

Question 21

what is activated at the onset of puberty?

Answer 21

the GnRH system

Question 22

describe puberty in girls

Answer 22

• growth spurt
• menarche
• pubic hair, breasts
• between ages of 8-14

Question 23

describe puberty in boys

Answer 23

• growth spurt
• testes
• penis
• pubic hair
• between ages of 8-16

Question 24

how is puberty activated?

Answer 24

neurons stimulate GnRH pulsatility → anterior pituitary releases LH & FSH → gonads produce sex steroids (testosterone/estrogen) → secondary sexual characteristics, growth, gametogenesis.