Sexual Differentiation Flashcards Preview

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Flashcards in Sexual Differentiation Deck (52):
1

What causes indifferent fetal gonads to differentiate into testes?

the product of the SRY/Tdy sex-determining gene (also blocks the expression of aromatase)

2

What happens if you block aromatase?

you prevent the conversion of testosterone to estrogen

3

What happens to the Wolffian ducts in the presence of testosterone?

they differentiate into male reproductive structures

4

What happens to Wollfian ducts in the absence of androgens or without the ability to respond to testosterone?

they regress and disappear

5

What happens to Mullerian ducts in the fetus?

they develop into female reproductive structures unless actively suppressed

6

What product of the SRY gene is responsible for reabsorption of the mullerian ducts and what cell type does it come from?

1) mullerian inhibiting factor (antimullerian hormone)
2) sertoli cells

7

Does testosterone stimulate the reabsorption of the mullerian ducts?

NO

8

What happens to a female embryo that has high testosterone levels?

both ducts will be retained

9

In what syndrome is high testosterone in the female usually seen and what deficiency is there?

1) congenital adrenal hyperplasia
2) 21 hydroxylase deficiency

10

What happens to an embryo is a teste is absent on one side?

the effects of testosterone are local - if the testis is absent on one side, the mullerian duct will be retained on that side

11

What happens to a male fetus that has functional testes but non-functioning testosterone receptors?

this means he is androgen insensitive and both sets of ducts will regress

12

By what week of development are testes obvious?

7 weeks

13

The structure of male external genitalia depends on what?

1) testosterone secreted by the fetal testis - without testosterone these structures develop into female external genitalia
2) conversion of testosterone to DHT (dihydrotestosterone) by 5a-reductase

14

What causes ambiguous genitalia in both sexes?

1) boys - insufficient androgens
2) excessive androgens

15

Which cells in the male makes testosterone and around what time do they start making it?

1) Leydig cells
2) weeks 6-8

16

What do sertoli cells produce? Around what weeks?

1) antimullerian hormone
2) androgen binding protein
3) weeks 9-12

17

What week of development do the external genetalia differentiate?

weeks 8-12

18

What hormone is required for differentiation of the male external genitalia?

Active 5a-reductase, which converts testosterone to dihydrotestosterone (DHT) - without DHT external genitalia will be female, regardless of the genetic, gonadal or hormonal sex

19

What is the genotype in Klinefelters Syndrome?

XXY

20

What pheotype is klinefelters?

male - presence of a Y chromosome (XXY)

21

What hormone levels are found in klinefelters?

1) testosterone low to normal
2) estrogen high

22

What symptoms are found in klinfelters?

1) feminization, including gynecomastia
2) normal spermatogenesis does not occur and FSH levels are high due to abnormal Sertoli cell function

23

What is androgen insensitivity?

testicular feminization - XY genotype with a defect in the testosterone receptor

24

What is the phenotype of androgen insensitivity?

male pseudohermaphrodites - internal testes but females externally

25

What happens to internal genitalia in males with androgen insensitivity?

No other internal genitalia besides testes
1) wolffian ducts don't develop
2) mullerian ducts regress (antimullerian hormone)

26

Why can breast development occur in androgen insensitive males?

peripheral conversion of testosterone to estradiol

27

What is absent in males with androgen insensitivity?

axillary and pubic hair

28

What is the treatment for androgen insensitivity?

1) testes are removed and patient is then given estrogen replacement therapy to maintain a normal female phenotype

29

What is the problem in a 5alpha reductase deficiency?

inability to convert testosterone to DHT

30

What are the consequences of 5alpha reductase deficiency?

1) male pseudohermaphrodites
2) differentiation of internal genitalia is normal (testosterone dependent)
3) differentiation of external genitalia are female (lack of DHT)

31

What can happen during puberty of those with 5alpha reductase deficiency?

phenotypic females until puberty when masculinization can occur in response to rising testosterone

32

What is the problem in Kallmann's Syndrome?

hypothalamic hypogonadism - decreased or absent GnRH secretion

33

What are the consequences of Kallmann's syndrome?

1) crytorchism
2) microphallus (small penis)
3) failure to undergo puberty
4) testes are immature and no spernatozoa
5) anosmia

34

What structures are normal in Kallmann's syndrome?

1) wolffian duct derived structures are normal - probably due to androgen production in response to placental hCG rather than fetal LH

35

What are the genetic links behind the anosmia in Kallmann's syndrome?

1) X-linked: KAL1 ansomin !
2) autosomal dominant: Kal2/FGFR 1

36

Does CAH affect males or females?

both!!!

37

What happens in CAH in males?

1) excess androgens leads to suppression of the HP axis leading to low LH and impaired testicular function (short term)
2) long term - rapid growth spurt along with early maturation of genitals - prococious puberty

38

What happens in CAH in females?

1) excess androgens lead to virulization
2) later effects - menstrual irregularities, excessive hair growth etc...

39

Why is CAH usually present at birth in females?

bc of the effects on external genitalia

40

What drives the secretion of LH and FSH?

GnRH

41

What are the targets for LH and FSH?

1) LH --> Leydig cells
2) FSH --> sertoli cells

42

What does LH and FSH do?

1) LH --> stimulate release of testosterone
2) FSH --> stimulates release of inhibin

43

What does inhibin do?

acts as a feedback inhibitor of FSH - acts exclusively on gonadotrops to inhibit FSH secretion only

44

what does testosterone do?

acts as a negative feedback regulator of LH and thus its own synthesis

45

What is testosterone's intratesticular actions?

to reinforce the effects of FSH on sertoli cells

46

What controls early steroidgenesis?

placental hCG bc fetal HTP axis is underdeveloped

47

What two times are leydig cells active?

1) in the fetus weeks 8-18
2) puberty - increase in number and activity

48

What type of interactions are present bw sertoli cells and leydig cells?

bi-directional interactions

49

What do sertoli cells do with testosterone?

1) can't produce testosterone
2) have receptors for testosterone
3) have enzymes to convert testosterone to estradiol

50

What is testosterone necessary for?

1) proper functioning of sertoli cells
2) spermatogenesis

51

What is ABP?

it binds testosterone and serves as a carrier in sertoli cells and in the sminiferous tubules

52

What levels of estrogen can men have?

circulating levels of estrogens can equal those as women - they are protected from feminization as long as tissue responsiveness remains normal