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203-T2 > How to make a boy or a girl > Flashcards

How to make a boy or a girl Flashcards

1
Q

What is the prevalence of genital abnormalities

A

1/4500

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2
Q

Making a boy/girl involved 3 main events

Describe the sex determination, during fertilisation

A
  • Inheritance of X or Y from father
  • At week 2 primordial germ cells (PGCs) arise from the epiblast
  • PGCs are pluripotent
  • PGC’ migrate to yolk sac stalk to avoid becoming imprinted. They later return travelling to the genital ridge (next to the kidney) and become the indifferent gonad
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3
Q

Making a boy/girl involved 3 main events

Describe the differentiation of gonad, week 5

A
  • At genital ridge: XX PGCs replicate at cortex; XY PGCs replicate at the medulla
  • Gonad gender decision relies on genetic switches and hormones

Genital transcription factors: Wt1, Sf1
Specific promoters of testis development: Sry,Sox9
Specific promoters of ovarian development: Wnt-4, FoxL2

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4
Q

At the urogenital ridge, bipotential gonad can either become a future ovary or a future testis. Which cells/precursors give rise to female

A

FUTURE OVARY
Supporting cell precursors –> follicular cells
Primordial germ cells –> oocytes
Steroidogenic precursors –> internal theca cells
Female PGCs –> oogonia (primary oocytes)
Sex cord cells–> granulosa (support and nutrify ovum)

Cortex –> layer of thecal cells –> secrete androgens before those generated by the follicles

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5
Q

At the urogenital ridge, bipotential gonad can either become a future ovary or a future testis. Which cells/precursors give rise to male

A

FUTURE TESTIS
Supporting cell precursors –> sertoli cells
Primordial germ cells –> pro-spermatogonia
Steroidogenic precursors –> leydig cells
Male PGCs–> spermatononica

Sry influences definition and identity of sertoli cells –> secretion of AMH (AMH suppresses female development pathway and induces cells in intermediate mesoderm to become leydig –> secrete testosterone)

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6
Q

Gonads are indifferent at start and linked to kidney development

Describe the origin, location and stages of kidney development

A

Origin: intermediate mesoderm (as the reproductive organs)

Location: between the somites and lateral plate (each side of the aorta)

Pronephros- diseappears soon after
Mesonephros - leaves remnants: ducts that become integral part of the reproductive system
Metanephros- becomes kidney

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7
Q

Making a boy/girl involved 3 main events

Describe the differentiation of internal and external genital organs, after week 5

A

Begin differentiation at week 8, formed from a priori identical primordium structures

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

  1. Paramesonephric (mullerian)
    - In female embryo mullerian duct is kept due to the absence of AMH. Mullerian duct becomes oviduct, uterus, cervix, upper part of vagina
    - In male embryo AMH causes mullerian duct regression and testosterone promotes wolffian duct differentiation
  2. Mesonephric (Wolffian)
    - Becomes epididymis, vas deferens and seminal vesicle
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8
Q

Why might an early embryo appear sexually ambiguous?

A

Both sexes show an elevated midline swelling - genital tubercle. This tubercle consists of

  • urethral groove (opening into the urogenital sinus)
  • paired urethral folds
  • paired labioscrotal swellings
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9
Q

How does the indifferent stage differentiate into male sex organs

A
  • Some testosterone is converted into DHT
    DHT stimulates development of the urethra, prostate and external genitals (scrotum and penis)
  • Genital tubercle –> PENIS
  • Fusion of the urethral folds –> spongy urethra
  • Labioscrotal swellings –> scrotum
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10
Q

How does the indifferent stage differentiate into female sex organs

A

Absence of DHT

  • Genital tubercle –> clitoris
  • Urethral folds remain open -> labia minora
  • Labioscrotal swellings –> labia majora
  • Urethral groove –> vestibule
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11
Q

Turners syndrome is caused by a chromosomal abnormality

Describe its genetics, overall presentation and diagnosis

A
  • Monosomy, XO
  • 1: 2500 (females only)
  • 99% non viable embryos
  • Survivors fail to sexually mature at puberty and exhibit several physical abnormalities
  • Diagnosis by amniocentesis
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12
Q

Turners syndrome is caused by a chromosomal abnormality

State 5 clinical signs

A
  • Short stature
  • Large carrying angle (elbow deformity)
  • Low hairline
  • Folds of skin
  • Coarctation of the aorta
  • Shield shaped thorax
  • Widely spaced nipples
  • Shortened metacarpal 4
  • Small finger nails
  • Poor breast development
  • Brown spots
  • No menstruation
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13
Q

Klinefelters syndrome is caused by a chromosomal abnormlity

Describe its genetics and overall presentation

A
  • Affects chromosome 47, XXY
  • 1 in every 600-1000 male births
  • Appear normal at birth, diagnosis confirmed through amniocentesis
  • Become infertile and exhibit some features associated with female development (e.g. gynecomastia)
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14
Q

Klinefelters is caused by a chromosomal abnormality

State 5 clinical signs

A
  • Taller than average
  • Reduced facial hair
  • Reduced body hair
  • Breast development (gynaecomastia)
  • osteoporosis
  • feminine fat distribution
  • small testes (testicular atrophy)
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15
Q

Describe true hermaphroditism

Think about chromosomal effect, possible cause and internal and external reproductive organs

A

EXTREMELY RARE

  • born with both ovarian and testicular tissue (ovotestis) - ambiguous genitalia due to a complicated mosaic karyotype
  • 46XX (SRY+), 45X (SRY+), and 45X
  • possible cause: two ova fertilised by two sperm that fuse to form a tetragametic chimera
  • external genital may be ambiguous or appear one gender
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16
Q

Describe female pseudohermaphroditism

Think about chromosomal effect, possible cause and internal and external reproductive organs

A
  • 46XX with virilisation (due to androgens)
  • internal sex organs are normal includingovarues
  • external appearance and genitals: male
  • features: fusion of labia and enlarged clitoris
  • possible cause: exposure to male hormones prior to birth (e.g. from congenital virilising adrenal hyperplasia_
17
Q

Describe male pseudohermaphroditism

Think about chromosomal effect, possible cause and internal and external reproductive organs

A
  • 46 XY with undervirilisation
  • External genitals: incompletely formed, ambiguous or clearly female
  • May have blind-ending vagina, absence of breast development, primary amenorrhoea
  • Testis can be normal, malformed or absent
  • Main causes: defective androgen synthesis, defective androgen action (e.g. receptor disorder), AIS, Leydig cell hypoplasia
18
Q

What is androgen insensitivity syndrome (AIS)

A

AKA Testicular feminisation

  • Affects 1: 20,000-64,000 male births
  • male hormones are normal
  • dysfunctional reception to these hormones

CAUSE OF MALE PSEUDOHERMAPHRODITISM

19
Q

What is leydig cell hypoplasia

A
  • Leydig cells dont secrete testosterone
  • Possible due to body insensitisation to LH
  • External genitalia normally female/slightly ambiguous
  • No female internal genitalia (uterus) develops

CAUSE OF MALE PSEUDOHERMAPHRODITISM

20
Q

Describe gonadal dysfunction

A

e.g. XY gonadal dysgenesis aka Swyers Syndrome

  • associated wiith XY Karytype
  • cause: alteration to Sry gene
  • external appearance: female (no menstruation)
  • no functional gonads (no testicular differentiation)
  • gonad may develop into malignancy
21
Q

State three examples of tract abnormalities

A

Uniconuate uterus
Agenesis of the vagina
Ductus deferens: unilateral or bilateral absence
Failure of mesonephric duct to differentiate

22
Q

Describe gonadal descent

A
  • more apparent and uncommon in males (cryptorchidism) than on females (undescended ovaries)
  • Cryptorchidism may be unilateral or bilateral occurring prematurely in 30% of cases. 3-4% may descend in first 2 years
  • Undescended ovaries are rare and usually detected in clinical fertility assessment

External genitalia is most common in male hypospadias

23
Q

Describe an example of abnormal external genitalia

A
  • most common in male hypospadias
  • 1:125 live male births
  • cause: failure of male urogenital folds to fuse
  • outcome: proximally displaced urethral meatus
24
Q

Is the brain and behaviour implicated in sex and gender?

What is the clinical application of this?

A
  • Sexual behaviour plays a part in gender identity. The brain acquires this independent of influence from androgens but instead from gene expression
  • 51 genes identified in mice expressed differently between male and females prior to the advent of androgens. They are active before gonad development
  • Potentially help surgeons decide which gender to opt in cases of genital malformation or of transsexualism

203-T2 (19 decks)

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