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Physiology 2 > Sexual differentiation and disorders (repro) > Flashcards

Sexual differentiation and disorders (repro) Flashcards

1
Q

Sexual determination

A

Genetically controlled process dependant on the ‘switch’ on the Y chromosome. Chromosomal determination of male or female.

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2
Q

Sexual differentiation

A

The process by which internal and external genitalia develop as male or female.

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3
Q

Similarities

A

The 2 processes are contiguous and consist of several stages

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4
Q

Gonadal sex

A
  • SRY gene creates the testis.
  • Sex determining region Y (SRY) switches on briefly during embryo development (>week 7) to make the gonad into a testis. In its absence an ovary is formed.
  • Testis develops cells that make 2 important hormones which are anti-Mullerian hormone (AMH) and testosterone
  • Products of the testis. influence further gonadal and phenotypic sexual development.
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5
Q

Gonadal development

A
  • After fertilisation, a pair of gonads develop which are biopotential.
  • Their precursor is derived from common somatic mesenchymal tissue precursors called the genital ridge primordia (3.5-4.5 weeks) on posterior wall of lower thoracic lumbar region.
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6
Q

Genital ridge

A

3 waves of cells invade the genital ridge

1) Primordial Germ cells - become sperm (male) or oocytes (female)
2) Primitive sex cords - become Sertoli cells (male) or Granulosa cells (female)
3) Mesonephric cells - become blood vessels and Leydig cells (male) or Theca cells (female)

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7
Q

1) Primordial germ cell migration

A
  • An initially small cluster of cells in the epithelium of the yolk. sac which expands by mitosis at 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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8
Q

2) Primitive sex cords

A
  • Cells from the germinal epithelium, overlying the genital ridge mesenchyme that migrate inwards as columns called the primitive sex cords
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9
Q

Primitive sex cords (Sertoli)

A

Male:

  • SRY expression
  • penetrate medullary mesenchyme and surround primordial germ cells to form testis cords (precursor of seminiferous tubules)
  • eventually become Sertoli cells which express AMH
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10
Q

Primitive sex cords (Granulosa)

A

Female:

  • No SRY expression
  • Sex cords ill defined and do not penetrate. deeply but instead condense in the cortex as small clusters around primordial germ cells (precursor of ovarian follicle)
  • eventually become Granulosa cells
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11
Q

3) Mesonephric cells

A
  • Originate in the mesonephric primordium which are just lateral to the genital ridges
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12
Q

Mesonephric cells in males

A

Act under the influence of pre-sertoli cells (express SRY) to form:

  • vascular tissue
  • Leydig cells (synthesise testosterone, do not express STY)
  • Basement membrane (contributing formation of seminiferous tubules and rete-testis
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13
Q

Mesonephric cells in females

A

Without the influence of SRY they form:

  • vascular tissue
  • Theca cells
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14
Q

Gonadal sex summary (males)

A

Invading cells:

  • Primordial germ cells = Spermatozoa (sperm)
  • Primitive sex cords = Sertoli cells (SRY, AMH)
  • Mesonephric cells = Leydig cells (Androgens)
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15
Q

Gonadal sex summary (females)

A

Invading cells:

  • Primordial germ cells = Oocytes
  • Primitive sex cords = Granulosa cells
  • Mesophrenic cells = Theca cells
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16
Q

Mullerian ducts

A
  • most important in female

- inhibited in the male by AMH

17
Q

Wolffian ducts

A
  • most important in the male stimulated by testosterone
18
Q

Internal sexual differentiation (male)

A
  • Epididymis
  • Testis
  • Vas deferens.
  • Urinary bladder
  • Seminal vesicle
  • Prostate gland
19
Q

Internal sexual differentiation (female)

A
  • Ovary
  • Oviduct
  • Degenerating Wolffian duct
  • Uterus
  • Urinary bladder
  • Vagina
20
Q

5-alpha-reductase & DHT

A
  • Testosterone converted in the genital skin to androgen DHT (dihydrotestosterone) by 5-alpha-reductase
  • DHT binds to testosterone receptor. and is more potent
21
Q

External differentiation by DHT

A

DHT causes differentiation of the male external genitalia:

  • clitorial area enlarges into penis
  • Labia fuse and become ruggated to form scrotum
  • Prostate forms
22
Q

Sex differentiation. summary (male)

A
  • Undifferentiated gonad develops into Testis due to SRY
  • AMH produced by Sertoli cells (regression of mullein ducts)
  • Testosterone produced by Leydig cells (differentiation and growth of wolffian duct structures seminal vesicles and vas deferens)
  • DHT produced by testosterone in the genital skin (fusion of labial scrotal folds growth of phallus and prostate)
23
Q

Sex differentiation summary (female)

A
  • Undifferentiated gonad develops. into ovary due to lack of SRY
  • Mullerian ducts differentiate and grow into uterine tubes, uterus and upper 1/3 of vagina
  • Regression of Wolffian ducts due to lack of androgens
  • Lack of androgen leads to vagina, labia. and clitoris
24
Q

Disorders of sexual differentiation

A

Gonadal dysgenesis (4 types) - sexual differentiation is incomplete. Usually missing SRY in male, or partial or. complete deletion of second X in female. Used as a general description of abnormal development of gonads.
Sex reversal - Phenotype does not match genotype, ie may be male genotypically but externally look like a female
Intersex - Have some components of both tracts or have ambiguous genitalia. Sex of infant difficult to determine.
- Patients prefer to be known with a ‘ disorder of sexual. differentiation’ or DSD
- ‘Pseudohermaphrodite’ and ‘testicular feminisation’ are obsolete

25
Q

Androgen insensitivity syndrome (AIS)

A
  • An XY makes testosterone but it has no effect
  • Testes form and make AMH so Mullerian ducts regress
  • Testosterone doesn’t act so no differentiation of Wolffian ducts
  • No DHT forms so no external male genitalia
    Complete AIS:
  • Incidence 1 in 20,000
  • Appear completely female at birth despite being XY
  • Undescended testes
  • Usually present with primary amenorrhea and lack of body hair
  • Ultrasound shows internal genitalia
  • Karyotype with male levels of androgens
  • Doesn’t respond to androgens so appears and often feels female
    Partial AIS:
  • incidence unknown as its a spectrum
  • present with varying degrees of penile and scrotal development from ambiguous genitalia to large clitoris
  • Surgery was universal but now fortunately considered optional or at least delayed. Decisions made on potential, very difficult for parents
26
Q

5-alpha-reductase deficiency

A
  • An XY produces testosterone and acts on it but doesn’t produce DHT
  • Testes form and AMH is made so Mullerian ducts regress
  • Testosterone allows Wolffian ducts to develop
  • Lack of DHT results in no external male genitals
  • Incidence varies enormously as autosomal recessive and can depend on inter-related marriage
  • All internal structures form, external structures do not develop
  • May appear mainly female or may have ambiguous genitalia
  • The degree of the enzyme block varies and so therefore does the presentation
  • Need to assess potential as high testosterone level, will occur at adrenarche and puberty may induce virilisation
27
Q

Turner syndrome

A
  • XO as only have 1 out of 2 X chromsomes
  • Failure of ovarian function
  • Incidence 1 in 3,000
  • ‘Streak’ ovaries
  • Uterus and tubes are present but small
  • Other defects in growth and development
  • May be fertile
  • Many have mosaicism
  • Hormone support of bones and uterus
28
Q

Congenital adrenal hyperplasia

A
  • An XX is exposed to high levels of androgens in utero
  • No SRY so no testes and no AMH
  • Mullerian ducts remain
  • Masculinised external genitalia.
  • Androgen levels usually not high enough to fully rescue Wolffian ducts
  • Incidence 1 in 15,000
  • Completeness of. the block varies
  • If enzyme absent then children may be wrongly gender. assigned at birth or may have ambiguous genitalia
  • possibility of salt wasting due to lack of aldosterone which can be lethal
  • Often require treatment with. glucocorticoids to correct feedback
29
Q

Hypothalamic Pituitary Adrenal Axis

A
  • The PVN in the hypothalamus releases Corticotropin releasing hormone (CRH) into the pituitary gland
  • Stimulates pituitary gland to secrete Adrenocorticotropic hormone (ACTH)
  • ACTH stimulates rapid uptake of cholesterol into the adrenal cortex
  • This upregulates cholesterol side-chain cleavage enzyme (P450scc)
  • This stimulates glucocorticoid (cortisol) secretion
30
Q

Conclusion

A
  • Correct sexual differentiation requires genetic, anatomical and endocrine components
  • Disorders are rare, but have allowed scientists to understand the requirements for normal development
  • Diagnosis and treatment of conditions of abnormal sexual differentiation requires a specialist team
  • Long term functioning of the person is now the primary issue rather than immediate ‘corrective’ surgery
31
Q

Glossery

A
  • Mullerian duct – embryonic ducts developing into female internal internal genitalia
  • Wolffian duct - embryonic ducts developing into male internal internal genitalia
  • Sex determining region Y (SRY) – important transcription factor on Y chromosome
  • Primordial germ cell – cells that develop into sperm or oocytes
  • Primitive sex cords – cells that develop into gonadal cells associated with germ cells
  • Mesonephric cells - cells that develop into gonadal cells that produce androgens
  • 5-alpha reductase – enzyme involved in development of male external genitalia
  • Gonadal dysgenesis – sexual differentiation is incomplete, usually abnormal development of gonads
  • Sex reversal – phenotype does not match genotype
    Intersex – some components of both male and female or ambiguous genitalia

Physiology 2 (38 decks)

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