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Reproduction (Physiology 2) > Sexual Differentiation & Disorders > Flashcards

Sexual Differentiation & Disorders Flashcards

1
Q

What is sexual determination?

A

Genetically controlled process dependent on the ‘switch’ on the Y chromosome. Chromosomal determination of male or female

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2
Q

What is sexual differentiation?

A

The process by which internal and external genitalia develop as male or female

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3
Q

What is the significance of sexual determination and differentiation?

A

The two processes are contiguous and consist of several stages

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4
Q

What is genotypic sex?

A

Genotypic sex refers to the embryo being genetically male (XY) or female (XX) = other combinations are possible

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5
Q

What does gonadal sex refer to?

A

Gonadal sex determines whether we have ovaries / testes

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6
Q

What is phenotypic sex?

A

Phenotypic sex is our external genitalia

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7
Q

What is legal sex?

A

Legal sex is what is stated on your birth certificate

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8
Q

What is gender identity?

A

Gender identity is how you feel you identify

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9
Q

How is gonadal sex determined?

A

> SRY gene on the short arm of the Y chromosome - creates the testis

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10
Q

Where is SRY gene expressed?

A

Only expressed in genetic males

In the absence of the Y chromosome ovaries develop

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11
Q

What is the SRY gene?

A

Sex determining region Y (SRY) essentially a transcription factor

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12
Q

What is the role of SRY gene?

A

SRY gene switches on briefly during embryo development (>week 7) to make the gonad into a testis. In its absence an ovary is formed

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13
Q

How does SRY gene cause male gonadal development?

A

Testis develops cells that make 2 important hormones that regulate the male differentiation pathway

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14
Q

What are the 2 male differentiation hormones produced by the testis?

A
  • Sertoli cells produce anti-Mullerian hormone (AMH)

- Leydig cells make testosterone

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15
Q

What is the significance of the Testis?

A

Products of the testis influence further gonadal and phenotypic sexual development.

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16
Q

What do the embryonic genital ridges develop into?

A

Genital ridges develop into testes / ovaries

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17
Q

What is the developmental product of the Mullerian ducts?

A

Mullerian ducts develop into uterine tube, uterus and upper part of vagina

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18
Q

What do the wolffian ducts develop into?

A

Wolffian ducts develop into the epididymis and vas deferens and part of the prostate

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19
Q

What are the chances of an embryo developing male or female gonads?

A

After fertilisation a pair of gonads develop which are bipotential - an embryo is equally capable of developing into a male or female

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20
Q

What determines the gonad differentiation pathway?

A

Their precursor is derived from common somatic mesenchymal tissue precursors called the genital ridge primordia (3½ - 4½ weeks) on posterior wall of lower thoracic lumbar region

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21
Q

What are the 3 cell types that invade the genital ridge?

A

Primordial Germ Cells
– become Sperm (male) or Oocytes (female)

Primitive Sex Cords
– become Sertoli cells (male) or Granulosa cells (female)

Mesonephric Cells
– become blood vessels and Leydig cells (male) or Theca cells (female)

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22
Q

How is primordial germ cell migration initiated?

A

An initially small cluster of cells in the epithelium of the yolk sac expands by mitosis at around 3 weeks

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23
Q

Where do the primordial germ cells migrate to?

A

They then migrate to the connective tissue of the hind gut, to the region of the developing kidney and on to the genital ridge

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24
Q

How long does primordial germ cell migration take?

A

completed by 6 weeks

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25
Q

What are the primitive sex cords?

A

Sertoli/Granulosa cells from the germinal epithelium that overlies the genital ridge mesenchyme migrate inwards as columns called the primitive sex cords

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26
Q

Outline the male gonadal differentiation

A
  1. SRY expression
  2. Penetrate medullary mesenchyme & surround PGCs to
    form testis cords
  3. Eventually become Sertoli Cells which express Anti-
    mullerian hormone (AMH).
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27
Q

Outline the female gonadal differentiation

A
  1. No SRY expression.
  2. Sex cords are ill defined & don’t penetrate deeply
  3. Instead condense in the cortex as small clusters around
    PGCs
  4. Eventually become Granulosa Cells
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28
Q

Why do the developed testes contain tube-like structures within sertoli cells?

A

As these cells move in to associate with primordial germ cells they form tube like structures with germ cells around - preface of what the developed gonads will look like - in spermatogenesis, developed testes have a tube like structure present with sertoli cells

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29
Q

Where do mesonephric cells originate?

A

These originate in the mesonephric primordium which are just lateral (sides) to the genital ridges

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30
Q

How are the male mesonephric cells infulenced?

A

In males they act under the influence of pre-sertoli cells and their growth factors (which themselves express SRY)

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31
Q

What do male mesonephric cells form under the influence SRY?

A
  • Vascular tissue
  • Leydig cells (synthesize testosterone, do not express
    SRY)
  • Basement membrane – contributing to formation of
    seminiferous tubules and rete-testis
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32
Q

What do the female mesonephric cells form without SRY expression?

A
  • Vascular tissue
  • Theca cells (synthesize androstenedione which is a
    substrate for estradiol production by the granulosa)
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33
Q

Summarise the male Gonadal development

A

Males
PGCs → Spermatozoa.
Primitive sex cords → Sertoli cells (SRY, AMH).
Mesonephric cells → Leydig cells (testosterone)

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34
Q

Summarise the female gonadal development

A

PGCs → Oocytes.
Primitive sex cords → Granulosa cells (estradiol).
Mesonephric cells → Theca cells (androstenedione)

35
Q

What are the 2 main structures involved in forming the internal reproductive organs?

A

Mullerian ducts

Wolffian ducts

36
Q

What are the Mulelrian ducts?

A

most important in female

inhibited in the male by AMH

37
Q

Describe the Wolffian ducts

A

most important in the male stimulated by testosterone

lack of stimulation by testosterone means regression in female

38
Q

Explain how the wolffian ducts undergo sexual differentiation

A

AMH in males causes mullerian ducts to regress

Testosterone causes wolffian ducts to develop into vas deferens, epididymis, seminal vesicle and part of the prostate

39
Q

How do the mullerian ducts undergo female sexual differentiation?

A

In absence of AMH mullerian ducts develop into uterine tube, uterus and upper 1/3 of cervix.

Wolffian duct degenerates due to lack of testosterone

40
Q

What is the fate of testosterone in the genital skin?

A

Testosterone is converted in the genital skin to the more potent androgen DHT (dihydrotestosterone) by 5-a-reductase

41
Q

What receptor does DHT bind to?

A

DHT also binds to the testosterone receptor, but is 10x more potent than testosterone

42
Q

What is the role of DHT in males?

A

DHT causes differentiation of the male external genitalia:

  • Clitoral area enlarges into penis
  • Labia fuse and become ruggated to form scrotum
  • Prostate forms
43
Q

What role does DHT play in females?

A

In females 5-a-reductase is present in the genital skin, but no (substrate) testosterone so no conversion to DHT occurs → female external genitalia pathway

44
Q

What is the early embryo genitalia?

A

In early embryo, male and female genitalia is the same

Genital tubercle, urethral fold with urogenital membrane in centre and genital swellings on the side to start off with

45
Q

Outline how the external male genitalia is differentiated

A

Male external genitalia pathway (5-a-reductase) converts testosterone → DHT causing genital tubercle to swell and become glans penis

Genital swellings swell further to produce scrotum and eventually testes will descend through the inguinal canal -

Skin becomes rugaeted
Urethral fold, folds upon itself to form a tube

46
Q

Explain the differentiation of female external genitalia

A

In females the genital tubercle eventually becomes the clitoris

The urethral fold becomes the opening to the vagina and labia
The genital swelling becomes the labia and majora
The urethral fold also forms the labia minora

In the absence of DHT female genitalia is produced

47
Q

What is gonadal dysgenesis?

A

Sexual differentiation is incomplete. Usually missing SRY in male, or partial or complete deletion of the second X in females. Also used as a general description of abnormal development of the gonads

48
Q

What is sex reversal?

A

Phenotype does not match genotype, ie may be male genotypically but externally look like a female

49
Q

What is intersex?

A

Have some components of both tracts or have ambiguous genitalia. Sex of infant difficult to determine

50
Q

What would cause an XY individual producing testosterone to have no effect on their gonadal identity?

A

non functioning testosterone receptors (gonadal dysgenesis)

51
Q

What is AIS?

A

Androgen insensitivity syndrome

52
Q

Explain the effect of AIS on gonadal development

A

AMH and regression of Mullerian ducts occurs

Wolffian ducts won’t develop as testosterone required

Patient ends up with no Mullerian or Wolffian ducts - no internal genitalia

External Genitalia is female as testosterone androgen receptor not working so won’t bind DHT

53
Q

Describe the effects of AIS on gonadal development and genitalia

A

Testes form and make AMH: Mullerian ducts regress
No differentiation of Wolffian ducts
No external Male genitalia

54
Q

What is the incidence of complete AIS?

A

Complete AIS - incidence 1:20,000

55
Q

Describe what a complete AIS patient would look like?

A

Appear completely female at birth and assigned female gender despite being XY.
Have undescended testes

56
Q

How would complete AIS be diagnosed?

A

Usually present with primary amenorrhoea. Lack of body hair is a clue.
Ultrasound scan and karyotype with male levels of androgens.
Never responded to androgen so appear and feel female.

57
Q

What is the incidence of partial AIS?

A

incidence unknown as is probably a spectrum

58
Q

What would a partial AIS patient present with?

A

Present with varying degrees of penile and scrotal development from ambiguous genitalia to large clitoris.

59
Q

How was partial AIS treated?

A

Surgery was universal but now fortunately considered optional or at least best delayed. Decisions made on potential. Very difficult for parents.

60
Q

What may be the cause of a lack of DHT being produced in an XY individual despite the presence of testosterone?

A

5-𝛼-Reductase Deficiency

61
Q

Explain the effects of 5-𝛼-Reductase Deficiency

A

Testes form and make AMH - Mullerian ducts regress
Wolffian ducts develop
No external male Genitalia

62
Q

What is the incidence of 5-𝛼-Reductase Deficiency?

A

Incidence varies enormously as autosomal recessive and can depend on inter-related marriage

63
Q

Describe the characteristics of 5-𝛼-Reductase Deficiency

A

Testes form, AMH acts, testosterone acts.
Internal structures form.
External structures do not develop.

May appear mainly female or may have ambiguous genitalia
The degree of the enzyme block varies and so therefore does the presentation

64
Q

What is the significance of puberty in patients with 5-𝛼-Reductase Deficiency?

A

Need to assess potential as high testosterone level which will occur at adrenarche and puberty may induce virilisation

65
Q

Describe Turners syndrome

A

45 XO (no 2nd X or Y)
Ovary as no SRY as no Y chromosome
Mullerian ducts present as no AMH - uterus, uterine ducts, vagina develop
Wolffian ducts regress as no testosterone
External Female genitalia
XO have failure of ovarian function

66
Q

Describe th eincidence of Turner’s syndrome

A

1:3000

67
Q

What are the clinical symptoms of Turner’s Syndrome?

A

‘Streak’ ovaries = ovarian dysgenesis - illustrates that we need 2 X’s for ovarian development
Uterus and tubes are present but small, other defects in growth and development.
May be fertile…many have mosaicism.
Hormone support of bones and uterus

68
Q

What is the result of an XX female being exposed to high androgen levels in utero?

A

> Congenital adrenal hyperplasia is the most common cause: 1:15,000.

virilisation of genitals: male genitalia

69
Q

What is the precursor of all steroid hormones?

A

steroid hormones derivatives of cholesterol as their precursor

70
Q

What is the significance of the adrenal glands in sexual differentiation?

A

Forms cortisol in adrenal cortex

Pathway block causes failure to synthesise cortisol has major effects

71
Q

Describe the structure of progesterones

A

All progesterones are cholesterol with 21Cs and the OH groups moved around

72
Q

Describe the androgen hormone structures

A

All androgens are cholesterol with 19Cs and the OH groups moved around

73
Q

What is the oestrogen hormones structure

A

18C cholesterol structure is the oestrogens (differ due to no. of OH groups)

74
Q

Which hormones are produced in the adrenal cortex?

A

Aldosterone and cortisol produced in adrenal glands (on top of kidneys)
Both 21C Cholesterol structures
Progesterone is easily converted into cortisol and aldosterone

75
Q

What enzyme is responsible for the conversion of prgoesterone to gluco/mineralocorticoids?

A

21 Hydroxylase enzyme converts progesterone into glucocorticoids and mineralocorticoids in the adrenal glands

76
Q

What would be the result of 21’OH mutations?

A

If 21 hydroxylase was mutated and non functional in an embryo, cortisol isn’t produced, no negative feedback on HPA and instead produces a lot of CRH and ACTH

77
Q

What is CRH?

A

Corticotropin releasing hormone

78
Q

What is the role of CRH?

A

Stimulates pituitary to secrete ACTH

79
Q

What is the role of Adrenocorticotropic hormone?

A

Stimulates rapid uptake of cholesterol into the adrenal cortex.
Upregulates cholesterol side-chain cleavage enzyme (P450scc). Increases glucocorticoid secretion

80
Q

What is the efefct of increased CRH and ACTH action?

A

Increased CRH and ACTH stimulate cholesterol uptake and adrenal cortex activity. Cortisol itself doesn’t rise because of enzyme block
Build up of androgens causes adrenal hyperplasia

Reduced feedback in pathway to produce steroid hormones

81
Q

What are the effects of CAH?

A

XX - Ovaries no SRY
No AMH so mullerian ducts develop normally to produce internal female genitalia

Testosterone produced so wolffian ducts will also grow

Masculinised external male genitalia due to testosterone production - but androgen levels aren’t normally high enough to rescue the Wolffian ducts

82
Q

What is the consequence of 21’OH missing in patients?

A

Completeness of the block varies.

If enzyme absent then children may be wrongly gender assigned at birth…or may have ambiguous genitalia

83
Q

Why may CAH be lethal?

A

Also in CAH need to be aware of the possibility of ‘salt-wasting’ due to lack of aldosterone, this can be lethal.
Need treatment with glucocorticoids to correct feedback

Reproduction (Physiology 2) (12 decks)

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