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Repro > Sexual differentiation and disorders > Flashcards

Sexual differentiation and disorders Flashcards

1
Q

What is sexual determination?

A
  • genetically controlled process dependent on the SRY gene on the Y chromosome
  • chromosomal determination of male or female
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2
Q

What is sexual differentiation?

A
  • The process by which internal and external genitalia develop as male or female
  • The type of gonads that develop determine what internal and then external genitalia we have
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3
Q

What are the several stages of sexual differentiation?

A
  • Genotypic sex - XX or XY
  • Gonadal sex - XY testes and XX ovaries
  • Phenotypic sex - internal and external genitalia (usually same as gonadal sex, but not always)
  • Legal sex - whats on birth certificate
  • Gender identity - what you yourself feels is appropriate
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4
Q

What determines the gonadal sex?

A
  • SRY (sex determining region Y) gene creates the testis
  • SRY switches on briefly during embryo development (> week 7) to make the gonad into a testis - in its absence, and ovary is formed
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5
Q

How does the SRY gene work?

A
  • Codes for a transcription factor
  • Binds upstream of DNA causing the gene to be read
  • Can also bind to the area itself and cause more of itself to be produced (amplification)
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6
Q

What are the two important cells that testis develop?

A
  • Sertoli cells produce anti-Mullerian hormone (AMH)
  • Leydig cells make testosterone
  • These products influence further gonadal and phenotypic sexual development
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7
Q

How does gonadal development occur?

A
  • after fertilisation, bipotential gonads develop
  • their precursor is derived from genital ridge primordia (somatic mesenchymal tissue precursors) on posterior wall of lower thoracic lumbar region
  • Wolffian duct will develop into male internal genitalia (VD, seminal vesicles, prostate)
  • Mullerian duct will develop into female
  • We have both ducts at this stage so any embryo can develop into either sex
  • Dependent on SRY the genital ridge will form ovaries or testes
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8
Q

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

A
  • Primordial germ cells - become sperm or oocytes. Migrate from the germ sac
  • Primitive sex cords - become Sertoli or Granulosa cells
  • Mesonephric cells - become blood vessels and Leydig or Theca cells - make androgens
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9
Q

How do primordial germ cells migrate to the genital ridge?

A
  • An initially small cluster of cells in the epithelium of the yolk sac expands by mitosis around 3 weeks
  • They then migrate to the connective tissue of the hind gut, to the region of the developing kidney and on to the genital ridge - completed by 6 weeks
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10
Q

How do the primitive sex cords get to the genital ridge?

A
  • Surround the gametes
  • Males = migrate in a tubular way
  • Females = surround them in clumps - males ovarian
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11
Q

How are the sertoli cells/ granulosa made?

A

Males:

  • SRY expression
  • penetrate the medullary mesenchyme and surround the PGCs to form testis cords
  • eventually become Sertoli cells which express AMH

Females

  • No SRY expression
  • Sex cords are ill defined and don’t condense in the cortex as small clusters around PGCs
  • Eventually become Granulosa cells
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12
Q

What do the mesonephric cells become?

A
  • Originate in the mesonephric primordium, just lateral to genital ridges
  • Males - act under influence of pre-sertoli cells (which express SRY) to form vascular tissue, leydig cells (synthesise testosterone), and basement membrane - contributing to formation of seminiferous tubules and rete-testis
  • Females - no influence of SRY, they form vascular tissue and Theca cells (synthesise androstenedione, a substrate for oestrogen production by granulosa)
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13
Q

Gonadal sex summary

A

Males

  • PGCs –> spermatozoa
  • Primitive sex cords –> Sertoli cells (express SRY, secrete AMH)
  • Mesonephric cells –> Leydig cells (secrete testosterone)

Females

  • PGCs –> Oocytes
  • Primitive sex cords –> Granulosa cells (oestradiol)
  • Mesonephric cells –> Theca cells (andronstenediol)
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14
Q

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

A
  • Mullerian ducts - female, inhibited by AMH in males

- Wolffian ducs - male, stimulated by testosterone. A lack of stimulation by testosterone causes regression

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15
Q

How does 5-alpha-reductase cause external differentiation?

A
  • Testosterone is converted in the genial skin to the more potent androgen DHT by 5-a-reductase
  • DHT binds to the testosterone receptor, but is 10x more potent
  • DHT causes differentiation of the male external genitalia
  • In the absence of DHT, the female external genitalia form - female still has 5-a-reductase, but no DHT
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16
Q

What does DHT cause in the male?

A
  • Differentiation of external genitalia
  • Clitoral area enlarges into penis
  • Labia fuse and become rugated to form scrote
  • Prostate forms
  • Urethral fold enlarges, folds over on itself and makes a tube
17
Q

What external differentiation occurs in females?

A
  • No DHT so the genital tubercle swells slightly and becomes the clitoris
  • Urethral folds become the labia majora and minora.
18
Q

Sex differentiation summary males

A

XY

  • SRY gene causes differentiation into testes
  • Sertoli cells produce AMH, which causes regression of mullerian ducts
  • Leydig cells produce testosterone, whih causes differentiaation and growth of Wolffian duct structures, seminal vesicles and VD
  • Testosterone is converted into DHT (10x more potent than testosterone) by 5-alpha reductase.
  • DHT causes external genitalia differentiation - fusion of labia to scrotal folds growth of phallus and prostate
19
Q

Sex differentiation summary females

A
  • XX
  • absence of SRY causes differentiation into ovary
  • Mullerian ducts differentiate and grow into uterine tubs, uterus and upper 1/3 of vagina
  • Lack of testosterone leads to vagina, labia and clitoris
  • Regression of Wolffian ducts
20
Q

What are the 3 main disorders of sexual differentiation?

A
  • Gonadal dysgenesis - Sexual differentiation is incomplete. Usually missing SRY in males or partial/complete deletion of second X in female. Also used as a general description of abnormal development of the gonads.
  • sex reversal - phenotype doesnt match genotype, e.g. may have male genotype but female external genitalia
  • Intersex - have some components of both tracts or ambiguous genitalia - difficult to determine sex of an infant
21
Q

What causes androgen insensitivity syndrome (AIS)?

A
  • Testosterone receptor not working (mutation of receptor or its secondary messenger system)
  • There is AMH so no mullerian ducts
  • There is DHT being made, but no effect - so female external genitalia
22
Q

What are the symptoms of complete AIS?

A
  • appear completely female at birth and assigned female gender despite XY
  • have undescended testes
  • usually present with primary amenorrhoea
  • lack of body hair is a clue
  • US scan and karyotype with male levels of androgens
  • Never responded to androgen so appear and feel female
23
Q

What are the symptoms of partial AIS?

A
  • Present with varying degrees of penile and scrotal development from ambiguous genitalia to large clitoris
  • Surgery was universal, but now optional or at least delayed
  • Decisions made on potential, very difficult for parents
24
Q

What happens in 5-alpha-reductase deficiency?

A
  • XY - SRY gene present
  • testes form, AMH and testosterone act
  • Internal structures form, but not external
  • May appear female or have ambiguous genitalia
  • The degree of enzyme block varies, and so does the presentation therefore
25
Q

What is Turner syndrome?

A
  • 45X0
  • Failure of ovarian function
  • “Streak” ovaries = ovarian dysgenesis - illustrates that we need 2Xs for ovarian development
  • Uterus and tubes are present but small, other defects in growth and development
  • may be fertile, may have mosaicism
  • hormones support of bone and uterus
26
Q

What causes congenital adrenal hyperplasia?

A
  • 21-hydroxylase defect - cannot make cortisol
  • make lots of progestagens - can only then make androgens from there
  • Lack of cortisol - want to make more progestagens, giving more and more androgens
27
Q

What are the symptoms of CAH?

A
  • have both mullerian and wolffian ducts - so both female and male internal genitalia
  • male external genitalia as have lots of Testosterone and so DHT
  • Completeness of the block varies
  • If enzyme is absent, then child may be wrongly gender assigned at birth, or have ambiguous genitalia
  • Also in CAH, need to be aware of possibility of ‘salt-wasting’ due to lack of aldosterone, this can be lethal
  • need glucocorticoid treatment to correct feedback
28
Q

What is the basic process of steroidogenesis?

A
  • All have 3 6C rings, then a 5C ring with a C tail
  • Cholesterol is the precursor for all steroids
  • Taken into cells, long chain is clipped using side-chain cleavage enzyme
  • If 22-27 are clipped = prostagens
  • Only difference between steroids is the positioning of OHs etc
  • Clip off 2 more from side chain - all androgens
  • Clip another 1 off - all oestrogens
29
Q

What is the hypothalamic pituitary adrenal axis?

A
  • Increased CRH causes pituitary to secrete ACTH
  • ACTH stimulates rapid cholesterol uptake into the adrenal cortex
  • Upregulates cholesterol side-chain cleavage enzyme
  • Increases glucocorticoid (cortisol) secretion
  • Negative feedback of cortisol on pituitary and hypothalamus
30
Q

What happens to the HPA axis in CAH?

A
  • Cortisol itself doesnt rise because of enzyme block

- No negative feedback > increase in CRH and ACTH - make more and more steroids, accumulating as androgens.

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