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Life Cycle > Sexual Differentiation and Disorders > Flashcards

Sexual Differentiation and Disorders Flashcards

1
Q

What is sexual determination?

A

genetically controlled process
dependent on the SRY switch in Y chromosome
this determines whether development will be directed towards M/F

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2
Q

What is sexual differentiation?

A

process by which internal and external genitalia develop as M or F

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3
Q

What is the nature of sexual determination and differentiation?

A

BOTH contiguous processes

BOTH traverse several stages

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4
Q

What are the stages of sex differentiation?

A
  • genotypic sex (XX or XY)
  • gonadal sex (testis or ovaries)
  • phenotypic sex (usually assessed by external genitalia at birth)
  • legal sex
  • gender identity
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5
Q

How does SRY gene dictate gonadal sex?

A

[In XY]
SRY gene expression = testis development

[in XX]
no SRY expression, ovaries develop

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6
Q

What is the SRY gene? What is its role?

A

= sex determining region Y (SRY)

present on Y chr

expression switched on briefly at >7weeks gestation

SRY = TF, which results in auto-activation of SRY gene and downstream cascades encouraging male pathway processes

makes gonad -> testis

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7
Q

What cell types does the testis develop? What hormones do they produce?

A

SERTOLI CELLS
anti-Mullerian hormone (AMH)

LEYDIG CELLS
testosterone

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8
Q

What is the nature of the undifferentiated gonad?

A

after fertilisation

gonads are BIPOTENTIAL

gonadal precursor (genital ridges) derived from COMMON SOMATIC MESENCHYMAL TISSUE

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9
Q

Where are the genital ridges primordia located?

A

[between 3.5-4.5wpc]

posterior wall of lower thoracic lumbar region

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10
Q

What is meant by undifferentiated gonads having BIPOTENTIALl?

A

have capacity to delelop into either M or F

via presence of both Mullerian and Wollfian ducts

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11
Q

What does the Mullerian duct become?

A

will develop into;

  • uterus
  • uterine tubes
  • upper 1/3 of vagina
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12
Q

What will the Wolffian duct become?

A

will develop into:

  • epididymis
  • vas Deferens
  • some aspects of prostate
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13
Q

What are the 3 waves of cells that invade the genital ridge?

A

PRIMORDIAL GERM CELLS
become sperm or oocytes

PRIMITIVE SEX CORDS
become Sertoli (m) or Granulosa (F) cells

MESONEPHRIC CELLS
become blood vessels and Leydig (m) or Theca (f) cells

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14
Q

What are ‘primordial germ cells?’

A
  • initially small cell cluster within yolk sac epithelium
  • initially diploid so divide by mitosis
  • migrate to connective tissue of hindgut
  • specifically to the developing kidney and then to genital ridge (completed by 6wks)
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15
Q

What are the primitive sex cords?

A

Cells from the germinal epithelium that overlies the genital ridge mesenchyme migrate inwards as columns

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16
Q

What do the primitive sex cords become in males?

A

SERTOLI CELLS

  • XY = SRY expression
  • Penetrate the medullary mesenchyme & surround the PGCs to form testis cords.
  • Eventually become Sertoli Cells which express Anti-mullerian hormone (AMH).
17
Q

What do the primitive sex cords become in females?

A

GRANULOSA CELLS

  • XX = No SRY expression
  • Sex cords are ill defined and do not penetrate deeply but instead condense in the cortex as small clusters around PGCs.
  • Eventually become Granulosa Cells.
18
Q

What are mesonephric cells?

A

originate from the mesonephric primordium (lateral to genital ridges)

MALES
act under influence of Sertoli precursors, forming:
- vascular tissue
- Leydig cells (Testosterone +ve, SRY -ve)
- basement membrane (maes seminiferous tubules and rete-testis)

FEMALES
without SRY expression, go onto form:
- vascular tissue
- theca cells (synthetic androstenedione = substrate for E2 production)

19
Q

What is the determination cascade for MALE sex?

A

Primordial germ cells -> spermatozoa

Primitive sex cords -> Sertolic cells (SRY, AMH)

Mesonephric cells -> Leydig cells (testosterone)

20
Q

What is the determination cascade for FEMALE sex?

A

Primordial germ cells -> oocytes

Primitive sex cords -> granulosa cells (E2)

Mesonephric cells -> theca cells (androstenedione)

21
Q

What is the function of granulosa cells that surround the primordial germ cell cluster?

A

to protect the oocytes held within

22
Q

What are the 2 main structures involved in internal reproductive organ formation?

A

MULLERIAN DUCT

  • most important in female
  • inhibited in males by AMH

WOLFFIAN DUCT

  • most important in males stimulated by testosterone
  • lack of stimulation by testosterone means regression in female
23
Q

How is dihydrotestosterone (DHT) produced?

A

testosterone converted to DHT
(by 5-a-reductase)

occurs in the genital skin

24
Q

What is DHT?

A

produced by 5-a-reductase

binds to testosterone receptors at higher potency than testosterone

causes differentiation of male external genitalia:

  • clitoral area -> penis
  • labia fuse and become rugged -> scrotum
  • prostate forms
25
Q

What happens if there is no DHT available?

A

female genitalia (external) are formed

e.g. in females, there is 5aRED but no testosterone so DHT cannot be made

26
Q

What is the link between 5-a-reducatse and baldness?

A

5-a-reductase expressed in scalp

inhibits hair follicles

leads to male-pattern baldness

27
Q

What is gonadal dysgenesis?

A

incomplete sexual differentiation

usually due to missing SRY expression in males

OR

partial or incomplete deletion of 2nd X chromosome in females

can also be used to describe general abnormal gonadal development

28
Q

What is sex reversal?

A

phenotype DOES NOT MATCH genotype

29
Q

What is intersex?

A

have some components of both Mullerian/Wolffian tracts or have ambiguous genitalia

difficult to determine sex of infant

usually prefer to be called disorder of sexual differentiation (DSD)

30
Q

What is androgen insensitivity syndrome?

A

XY individual

testosterone is produced but has no effect
e.g. issue with testosterone receptor or the downstream cascade

RESULT: regression of wolffian ducts (no internal male genitalia)
still have DHT but no wolffian ducts so no external male genitalia

31
Q

What is COMPLETE AIS?

A

AIS = androgen insensitivity syndrome

incidence 1:20,000

appear completely female at birth (therefore assigned female gender, even though XY)

have undescended testes

32
Q

How is complete AIS usually diagnosed?

A

AIS = androgen insensitivity syndrome

  • primary amenorrhoea
  • no body hair

USS and karyotype analysis
male level of androgens

never responded to androgen so will often feel female

33
Q

What is PARTIAL AIS?

A

AIS = androgen insensitivity syndrome

incidence unknown as most likely a spectrum

varying degrees of penile and scrotal development or ambiguous genitalia to large clitoris

surgery used to be universal but now considered optional

decisions made on potential - so can be difficult for parents

34
Q

What happens with 5-a-reducatase deficiency?

A

XY individual
testosterone made but no DHT as no 5-a-reductase or deficiency

this is autosomal recessive (therefore higher incidence in consanguineous marriage)

incidence varies

testes form, AMH acts, testosterone acts

internal structures form

external structures do not develop

may appear mainly female or have ambiguous genitalia

degree of deficiency informs on presentation

AT PUBERTY
need to re-assess
high [testosterone] at adrenarche may induce virilisation

35
Q

What is Turner’s syndrome?

A

X- (lacks complete 2nd X chr)

incidence 1:3000

causes failure of ovarian function

‘streak’ ovaries (ovarian dysgenesis)

uterus and tubes are small but present
also other defects in growth and development

may be fertile
many have mosaicism

hormone support of bones and uterus

36
Q

What is congenital adrenal hyperplasia?

A

(CAH)

most common cause of gonadal dysgenesis

incidence 1:15,000

XX individual
exposed to high levels of androgens in utero

completeness of block varies

most commonly 21alpha hydroxylase

then 17-alpha-hydroxylase or 11-beta hydroxylase

can be wrongly assigned at birth or have ambiguous genitalia

Salt-wasting crisis: due to lack of aldosterone (can be lethal)

RX: glucorticoids to correct feedback loop

Life Cycle (29 decks)

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