Sexual Differentiation Flashcards
1
Q
What three main events dictate sexual differentiation in humans?
A
- Sex determination during fertilization: X or Y chromosome
- Differentiation of gonads at week 5
- DIfferentiation of internal and external genital organs after week 5
2
Q
What happens in the first 2-5 weeks of genital differentiation?
A
- at 2 weeks the primordial germ cells (PGCs) migrate from the epiblast
- these will become the gonads, however, they are still pluripotent
- they migrate to the yolk sac to avoid becoming imprinted before returning to the genital ridge (next to the kidney) and become the indifferent gonads
3
Q
Which genetic switches are important in the development of Gonads?
A
- General transcription factors
- Wt1, Sf1
- Specific promotors of testis development
- Sry, Sox9
- Specific promotors of ovarian development
- Wnt-4, FoxL2
4
Q
What are the cell lines pathways when the PGC’s reach eh urogenital ridge and become bipotential gonad cells?
- Supporting cell precursor –>
- Primordial germ cells (PGCs) –>
- Steroidogenic precursors –>
A
- Supporting cell precursor –>
- Follicular cells in future ovaries
- Sertoli cells in future tesits
- Primordial germ cells (PGCs) –>
- Oocytes in future ovaries
- Pro-spermatogonia in future testis
- Steroidogenic precursors –>
- Internal theca cells in future ovaries
- Leydig cells in future testis
5
Q
What is the function of female gonad cells?
A
- Sex cord cells form the granulosa which nutrify and support the ovum
- the Cortex forms the thecal cells
- these secrete androgens before the follicular androgens are released
6
Q
What is the function of male gonad cells?
A
- Sertoli cells and the influence of Sry gene leads to the secretion of Anti-Mullerian Hormone (AMH)
- this suppresses the female development pathway
- induce cells in the intermediate mesoderm to become Leydig cells
- which secrete testosterone
7
Q
What are the three main stages of kidney development?
A
- they develop from the intermediate mesoderm (same as the reproductive organs) between the somites and the lateral plate (either side of the aorta)
- Pronephros: disappears soon after forming
- Mesonephros: leaves some remnants
- the mesonephric duct is left behind which is used by the reproductive system
- Metanephros: becomes the kidney
8
Q
Give an overview of the development of the Internal genital organs
A
- begin differentiation around week 8
- they are formed from a priori identical primordium structures
- embryos of both sexes possess two sets of paired ducts which they develop from
-
paramesonephric: Müllerian
- women
-
mesonephric: Wolffian (kidney development)
- testosterone promotes differentiation of Wolffian duct in men
-
paramesonephric: Müllerian
- embryos of both sexes possess two sets of paired ducts which they develop from
9
Q
Explain the male embryo pathway from the bipotential gonads
A
- AMH causes Mullerian duct to regress
- testosterone stimulates differentiation of the Wolffian duct
- Wolfian duct differentiates to
- Epididymis
- Vas deferens
- Seminal vesicle
10
Q
Give an overview of the development of the external genital organs
A
- embryos of both sexes show an elevated midline - genital tubercle
- the tubercle consists of
- urethral groove (opens into the urogenital sinus)
- paired urethral folds
- paired labioscrotal swellings
11
Q
Explain the development of male external genital organs
A
- Some testosterone is converted into dihydrotestosterone (DHT)
- DHT stimulates the development of the urethra, prostate and external genitals (scrotum and penis)
- Genital tubercle increases in size => penis
- Fusion of the urethral folds occur to form => spongy urethra
- Labioscrotal swellings => scrotum
12
Q
Explain the development of the female external genital organs
A
- Absence of DHT
- Genital tubercle slightly less swelling => clitoris
- Urethral folds remain open => labia minora
- Labioscrotal swellings => labia majora
- Urethral groove remains open => vestibule of the vulva
13
Q
What are the six most common types of sex differentiation abnormalities?
A
- Chromosomal
- Turner’s syndrome
- Klinefelter’s syndrome
- Hermaphroditism
- True
- Female and Male Pseudo
- Gonadal dysfunction
- Swyer’s Syndrome (XY gonadal dysgenesis)
- Tract abnormalities
- Gonadal descent
- External genitalia
14
Q
What is Turner’s syndrome?
- presentation
- how is it diagnosed?
A
- A chromosomal monosomy (XO) abnormality that effects 1:2500 women, 99% of embryos are not viable
- survivors fail to sexually mature at puberty
- they exhibit several physical abnormalities
- rudimentary gonads, widely spaced nipples,
- construction of the aorta
- no menstruations
- nevi (brown spots)
- Diagnosis is confirmed through amniocentesis
15
Q
What is Klinefelter’s Syndrome?
- presentation
- how is it diagnosed?
A
- Chromosomal XXY that effects 1:600-1000 males
- appears normal at birth but are infertile
- they exhibit features associated with female development
- gynaecomastia and position of fat
- testicular atrophy
- osteoporosis
- Diagnosis confirmed through amniocentesis
22
Q
What tract abnormalities are there?
A
- Uterine: unicornuate uterus
- Vagina: agenesis
- Ductus Deferens: unilateral or bilateral absences, due to failure of the mesonephric duct to differentiate
- in 98% of men with Cystic fibrosis have a missing epididymis and the vas deferens, seminal vesicles and ejaculatory ducts are atrophic or completely absent
