Anti-mullerian hormone Produced from sertoli cells under the influence of Sry gene - Suppresses female development pathway - Induces Leydig differentiation (from intermediate mesoderm)

Sexual differentiation Flashcards by aderonke adesanoye

Prevalence of genital abnormalities

1 in 4500

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Sex determination

Occurs during fertilisation

X or Y chromosome is inherited from father.

X chromosome inherited from mother.

XY- male
XX- female

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Origin of primordial germ cells

Arise from the epiblast are week 2

- Pluripotent cells

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Differentiation of primordial germ cells

Firstly migrates to yolk sac
- Prevents imprinting

Later returns next to genital ridge (next to kidneys)
- Indifferent gonad

XX- replicate at cortex
XY- replicate at medulla

Gender decision is dependant on genetic switches and hormones

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Genetic switches

Transcription factors
- Wt1, Sf1

Specific promoters of testis development

Specific promoters of ovarian development

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Specific promoters of testis development

A type of genetic switch that determines the male sex.

Examples

Sry
Sox9

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Supporting cell precursors

Bipotential gonad cells that originate from the urogenital ridge

Differentiates into

Follicular cells in ovaries
Sertoli cells in testis

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Primordial germ cells

Bipotential gonad cells that originate from the epiblast

Differentiates into

Oocytes in ovaries
Pro-spermatogonia cells in testis

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Steroidogenic precursor cells

Bipotential gonad cells from the urogential ridge

Differentiates into

Internal theca cells in ovaries
Leydig cells in testis

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Differentiation of sex cord cells in females

Differentiates into granulosa in ovaries

- Supports and nutrifyes the ovum

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Differentiation of the cortex in females

Forms layer of theca cells

- Secretes androgens

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Sry

Specific genetic promoter of testis development.

Influences definition and identity of Sertoli cells
- Stimulates AMH secretion.

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AMH

Anti-mullerian hormone

Produced from sertoli cells under the influence of Sry gene

Suppresses female development pathway
Induces Leydig differentiation (from intermediate mesoderm)

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Origin of kidney

Intermediate mesoderm

- Between somites and lateral plate

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Pronephros

First stage of kidney development

- Disappears right after formation

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Mesonephros

Structure formed in the second stage of kidney development

Leaves ducts before degeneration
- Ducts become integral part of the reproductive system

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Metanephros

Final stage of kidney development that fully develops into the kidney

Time of internal genital organs differentiation

Week 8

Origin of internal genitial organs

All embryos contain two sets of paired ducts at the start

Paramesonephric–> Mullerian
Mesonephric—> Wolffian

Mullerian duct

Kept in the female embryo
- Due to the absence of anti-Mullerian hormone

The duct is composed of:

Oviduct
Uterus
Cervix
Upper vagina

Differentiation of the male genital organs

In the male embryo, AMH and male hormones are secreted
- AMH regresses the mullerian/ paramesonephric duct

Testosterone promotes Wolffian duct differentiation

Wolffian duct

Composed of

Epididymis
Vas deferens
Seminal vesicle

Genital tubercle

Initial development of external genital organs in both sexes

Both show an elevated midline swelling.

Composed of

Urethral groove
Paired urethral folds
Paired labioscrotal swellings

Development of male external genital organs

Some testosterone—> DHT

DHT stimulates the development of:

Urethra (spongy urethra from urethral fold fusion)
Prostate
Scrotum (from labioscrotal swellings)
Penis (from genital tubercle)

Development of female external genital organs

No DHT stimulates: - Clitoris (from genital tubercle) - Labia minora (from open urethral fold) - Labia majora (labioscrotal swelling) - Vestibule (from urethral groove)

Turner's syndrome - Genetics - Prevalence - Prognosis of embryos - Diagnosis

Monosomy - XO 1:2500 females 99% of embryos are not viable Diagnosed by assessing karyotype from amniocentesis

Turner's syndrome | - Clinical presentation [6]

Short stature - Low oestrogen Underdeveloped gonads Webbed neck Failure to undergo puberty/ menstruation Constricted aorta Shorter metacarpal IV/ small finger nails

Klinefelter's syndrome - Genetics - Prevalence - Diagnosis

47 XXY 1:600-1000 male births Appear normal at birth - Diagnosed via karyotyping (amniocentesis)

Klinefelter's syndrome | - Presentation

Tall height - Excess oestrogen Reduced facial/body hair Gynaecomastia Osteoporosis Feminine fat distribution Testicular atrophy

True hermaphrodite - Description' - Genetics - Possible cause

``` Rare condition where an individual is born with ovarian and testicular tissue. Genital may be - Ambigous - Male/ female Genetics - 46 XX (SRY+) - 45 X (SRY +) - 45 X ``` Cause - Two ova fertilised by two sperm and fused

Female pseduohermaphrodite

46 XX with virilization - Excess androgens Normal internal genital organs Male external appearance and genitals Fusion of labia, large clitoris Possible cause - XS androgen exposure during pregnancy (i.e in CAH)

Male pseduohermaphrodite - Genetics - External genitalia - Testis - Other features

46, XY with undervirilization External genital - Incomplete/ ambiguous/ female Other features - Blind-ending vagina - No breast - Primary amenorrhea Testis - Normal/ malformed/ absenct

Male pseduohermaphrodite | - Main causes

Defective androgen synthesis in utero Defective androgen action (receptor disorder)

Androgen insensitivity syndrome - Other name - Prevalence - Description

Known as testicular feminization 1:20000-64000 male births Dysfunction receptor to male hormones

Leydig cell hypoplasia

Possibly caused by insensitivity to LH Leydig cells do not produce LH Features - External genitalia female/ slightly ambigous - No female internal genitalia

XY gonadal dysgenesis

Also known as Swyer's syndrome - Sry gene alteration External- female No functional gonads - No testicular differentiation - No menstruation - May develop into malignancy

Unicornuate uterus

Congenital mullerian anomaly Only connected to one fallopian tube+ ovary - Endometrial space is halved.

Cryptotchidism - Description - Prevalence

Undescended testis - Can be unilateral/ bilateral -30% premature males, 3-4% term males

Undescended ovaries

Much less common than cryptochidism Detected with clinical fertility assessment

Male hypospadia - Description - Prevalence

Failure of male urogenital folds to fuse - Proximal displaced urethral meatus 1:125 male births

Sexual behaviour

Gene expression is important in acquiring gender identity - Inactivation of genes from x chromosome showed predisposition to transexualism in animal studies. Gene expression in brain takes place way before gonadal development (Week 2)

Differing gene expression in male and female brain

Mouse embryos showed 51 genes different between male and female - Active genes before gonads develop (week 2)