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203: Theme 2: Reproductive system, fetal development, pregnancy and birth > Sexual differentiation: how to make a boy or girl > Flashcards

Sexual differentiation: how to make a boy or girl Flashcards

1
Q

Sex determination

A

Sex is determined at fertilisation

Inheritance of X/Y from father

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2
Q

Gonad origin

A

At week 2 primordial germ cells arise from the epiblast

They are pluripotent

Migrate to yolk sac stalk to avoid becoming imprinted

Later return, travelling to the genital ridge and becoming the indifferent gonad

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3
Q

Primordial germ cells at the genital ridge

A

XX PGCs replicate at cortex

XY PGCs replicate at the medulla

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4
Q

Gonad gender decision relies on

A

Genetic switches

Hormones

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5
Q

Genetic switches

A

General transcription factors

Specific promoters of testis development

Specific promoters of ovarian development

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6
Q

Fate of female PGCs

A

Oogonia

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7
Q

Fate of sex cord cells

A

Granulosa

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8
Q

Fate of cortex

A

Layer of thecal cells

Secret androgens before those generated by the follicles

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9
Q

Fate of PGCs

A

Spermatogonia

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10
Q

Kidney development

A

Origin: intermediate mesoderm

Where: between the somites and lateral plate

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11
Q

3 stages of kidney development

A

Pronephros
- disappears soon after

Mesonephros
- leaves remnants

Metanephros
- becomes kidney

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12
Q

Mesonephros

A

Middle stage of kidney development

Leaves behind ducts that become integral part of the reproductive system

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13
Q

Internal genital organs

A

Begin differentiation at about week 8, formed from identical primordium structures

Embryos of both sexes possess two sets of paired ducts at the start

  • paramesonephric
  • mesonephric
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14
Q

Mullerian duct female

A

Paramesonephric

In female embryo duct is kept due to absence of AMH

Mullerian duct

  • oviduct
  • uterus
  • cervix
  • upper part of the vagina
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15
Q

Mullerian duct male

A

In male embryo

  • AMH causes mullerian duct regression
  • testosterone promotes wolffian duct differentiation
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16
Q

Wolffian duct

A

Mesonephric

Wolffian duct

  • epididymis
  • vas deferens
  • seminal vesicle
17
Q

External genital organs

A

At first embryos of both sexes show an elevated midline swelling- genital tubercle

Tubercle consists:

  • urethral groove
  • paired urethral folds
  • paired labioscrotal swellings
18
Q

Development of male external genital organs

A

Some testosterone is converted into dihydrotestosterone

DHT stimulates development of the urethra, prostate and external genitals (scrotum and penis)

Genital tubercle –> penis

Fusion of urethral folds –> spongy urethra

Labioscrotal swellings –> scrotum

19
Q

Development of female external genital organs

A

Absence of DHT

Genital tubercle –> clitoris

Urethral folds remain open –> labia minora

Labioscrotal swellings –> labia majora

Urethral groove –> vestibule

20
Q

Abnormalities

A

Chromosomal

Hermaphroditism

Gonadal dysfunction

Tract abnormalities

Gonadal descent

External genitalia

21
Q

Turner’s Syndrome

A

Monosomy, XO

1:2500 females (does not affect males)

99% non-viable embryos

Survivors fail to sexually mature at puberty

Exhibit several physical abnormalities

Diagnosis confirmed through amniocentesis

22
Q

Physical abnormalities of Turner’s syndrome

A

Short stature

Low hairline

Shield shaped thorax

Widely spaced nipples

Shortened metacarpal

Small finger nails

Characteristic facial features

Constriction of aorta

Poor breast development

Elbow deformity

Rudimentary ovaries

No menstruation

23
Q

Klinefelter’s Syndrome

A

47, XXY

1:600-1000 male births (does not affect females)

Birth appear normal (undetected

Become infertile

Exhibit some features associated with female development (e.g. gynaecomastia)

Diagnosis confirmed through amniocentesis

24
Q

Physical abnormalities of Klinefelters syndrome

A

Taller than average height

Reduced facial hair

Reduced body hair

Breast development

Osteoporosis

Feminine fat distribution

Small testes

25
Q

True hermaphroditism

A

Extremely rare

Born with body ovarian and testicular tissue

46XX (SRY), 45X (SRY) and 45X

Possible cause e.g. two ova fertilised by two sperm that fuse to form a tetragametic chimera

External genitals may be ambiguous or appear to be female or male

26
Q

Female pseudohermaphrodite

A

46, XX with virilisation (due to androgens`0

Internal sex organs are normal

External appearance and genital: male

Features:

  • fusion of labia
  • enlarged clitoris

Possible cause: exposure to male hormones prior to birth

27
Q

Male pseudohermaphrodite

A

46, XY with undervirilisation

External genitals: incompletely formed, ambiguous or clearly female

Some features: blind ending vagina, absence of breast development, primary amenorrhoea

Testis: normal, malformed or absent

Main causes

  • defective androgen synthesis
  • defective androgen action
28
Q

Androgen insensitivity syndrome

A

aka testicular feminisation

Affects 1:20000-64000 male births

Male hormones are normal

Dysfunctional receptor to these hormones

29
Q

Leydig cell hypoplasia

A

Leydig cells do not secrete testosterone

Possible reason: body insensitive to LH

External genitalia normally female/ slightly ambiguous

No female internal genitalia develop

30
Q

Gonadal dysfunction

A

e.g. XY gonadal dysgenesis (Swyer’s Syndrome)

Associated with XY karyotype

Cause: alteration to Sry gene

External appearance: female (no menstruation)

No functional gonads (no testicular differentiation)

Gonad may develop into malignancy

31
Q

Tract abnormalities

A

Uterine: e.g. unicornuate uterus

Vagina: e.g. agenesis

Ductus deferens: unilateral or bilateral absence, failure of mesonephric duct to differentiate

32
Q

Gonadal descent

A

More apparent and common in males than on females

33
Q

Cryptorchidism

A

May be unilateral/ bilateral

Occurs 30% premature; 3-4% males

Descent may take place during year 1

34
Q

Undescended ovaries

A

Quite rare

Detected in clinical fertility assessment

35
Q

Male hypospadia

A

1:125 live male births

Failure of male urogenital folds to fuse

Outcome: proximally displaced urethral meatus

36
Q

The brain and behaviour

A

What makes us a boy or girl: sexual behaviour

Gender identity from gene expression, given the correlation between inactivation of genes from the X chromosome and predisposition to transexualism

203: Theme 2: Reproductive system, fetal development, pregnancy and birth (25 decks)

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