Sexual Differentiation & Disorders Flashcards
Describe Sexual determination
A genetically controlled process dependent on the ‘switch’ on the Y chromosome. Chromosomal determination of male or female
Describe Sexual differentiation
The process by which internal and external genitalia develop as male or female
What is the relationship between Sexual determination & differentiation?
- The two processes are contiguous
- Both consists of several stages
What are the different types of sex differentiation?
- Genotype sex
- Gonadal sex
- Phenotype sex
- Legal sex
- Gender identity
What is the SRY gene?
The SRY gene creates the testi’s. It is the sex determining region.
How does the SRY gene work?
The Sex determining region Y switches on briefly during embryo development at >week 7 to make a gonad into a testi.
- In it’s absence, an ovary is formed
What two important hormones do testi’s develop?
- Anti Mullerian hormone (AMH)
- Testosterone
Why are these 2 hormones important?
Products of the testis influence further gonadal and phenotype sexual development
What happens during Gonadal development?
- After fertilisation, a pair of gonads develop which are bipotential
- Their precursor is derived from common somatic mesenchymal tissue precursors called the genital ridge primordia (3½ - 4½ weeks) on posterior wall of lower thoracic lumbar region
Describe the events that occur during the genital ridge
3 waves of cells invade the genital ridge
- primordial germ cells: become sperm or oocytes
- Primitive sex cords: Become Sertoli cells or Granulosa cells
- Mesonephric cells: Becomes Leydig cells or Theca cells
Describe the Primordial Germ cell migration
- An initially small cluster of cells in the epithelium of the yolk sac 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 the genital ridge (completed by 6 weeks)
Describe the primitive sex cords
Cells from the germinal epithelium that overlies the genital ridge mesenchyme migrate inwards as columns called the primitive sex cords.
Describe the characteristics of the Male primitive sex cords
- SRY expression
- Penetrate medullary mesenchyme & surround the primordial germ cells to form testi’s cords - Precursor of seminiferous tubules
- Eventually become Sertoli cells which express AMH
Describe the characteristics of the female primitive sex cords
- 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
Describe the mesonephric cells
Originiate in the mesonephric promordium which are just lateral to the genital ridge
What does the mesonephric cells influence in males?
In males they act under the influence of pre-Sertoli cells to form:
- Vascular tissue
- Leydig cells (synthesise testosterone, don’t express SRY)
- Basement membrane: contributing to formation of seminiferous tubules and retetstis
What does the mesonephric cells influence in females?
Without the influence of STY they form:
- Vascular tissue
- Theca cells
In Males, what do the invading cells become?
Primordial cells become Spermatozoa
Primitive sex cords become Sertoli cells (STY,AMH)
- Mesonephric cells become Leydig cells (Androgens)
In Females, what do the invading cells become?
- Primordial germ cells become Oocytes
- Primitive sex cords become Granulosa cells
- Mesonephric cells become Theca cells
What are the two internal reproductive organs?
- Mullerian cells
- Wolffian ducts
Briefly describe the Mullerian ducts?
- Most important in females
- Inhibited in the male by AMH
Briefly describe the Wolffian ducts?
- Most important in males
- Stimulated by testosterone
- Lack of stimulation means regression in males
Why does 5 ã reductase do?
- Converts Testosterone in the genital skin to the more potent androgen DHT (Dihydrotestosterone)
- DHT binds to the receptors, but is more potent than testosterone
What does DHT cause in the male external genitalia?
Causes differentiation
- Clitoral area enlarges into penis
- Labia fuse and becomes ruggated to form scrotum
- Prostate forms
Briefly describe the sex differentiation summary for males
1). Sertoli cells release AMH which causes regression of Müllerian ducts
2). Leydig cells release testosterone which causes differentiation and growth of Wolffian duct structures seminal vesicular and vas deferens
3). Genital skin releases DHT which causes fusion of labial scrotal folds of phallus and prostate
Briefly describe the sex differentiation summary for females
1). Müllerian ducts differentiate and grow into uterine tubes, uterus and upper 1/3rd of vagina
2). Regression of Wolffian ducts due to lack of androgens
3). Lack of androgen leads to vagina, labia & clitoris
What are the different disorders of sexual differentiation?
- Gonadal dysgenesis: Sexual differentiation is incomplete. Usually missing SRY in males.
- Sex reversal: Phenotype does not match genotype
- Intersex: Have some components of both tracts or have ambiguous genitalia. Sex of infant difficult to determine
Gonadal dysgenesis: What happens if in an CY individual, Testosterone is made but has no effect?
Androgen Insensitivity Syndrome (AIS)
What occurs in Androgen Insensitivity Syndrome? (AIS)
- Testes form and make AMH so Müllerian ducts regress
- No differentiation of Wolffian ducts
- No external male genitalia
Describe the features of Androgen Insensitivity syndrome
Complete AIS: incidence 1:20,000
- Appear completely female at birth and assigned female gender despite being CY.
- Have undescended testes
Describe the diagnostical features of Androgen Insensitivity syndrome
- Usually present with primary amenorrhoea
- Lack of body hair is a clue
- Ultrasound scan and karyotype with male levels of androgens
- Never responded to androgen so appear and often feel female
Describe partial AIS
- Incidence is unknown as it is probably 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
Gonadal dysgenesis: what happens if in an XY individual, Testosterone is made but not DHT?
Causes 5 ã reductase deficiency
What occurs during 5-α-reductase deficiency?
- Testes form and make AMH so Mullerian ducts regress.
- Wolffian ducts develop
- No external male genitals.
Describe the incidence rate of 5-α-reductase deficiency
- Incidence varies enormously as autosomal recessive and can depend on inter-related marriage
What happens during 5-α-reductase deficiency?
- Testes form, AMH acts, testosterone acts.
- 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.
5-α-reductase deficiency, what happens at puberty?
Need to assess potential as high testosterone level which will occur at adrenarche and puberty may induce virilisation
Breifly describe the Turner syndrome
- Incidence rate of 1:3000
- XO have failure of ovarian function
- 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
Gonadal dysgenesis: What happens if XX female is exposed to high levels of androgens in utero?
Congenital adrenal Hyperplasia
What does the Corticotropin releasing hormone do? (CRH)
Stimulates pituitary to secrete ACTH
What does the adrenocorticotropic hormone do?
- rapid uptake of cholesterol into the adrenal cortex.
- upregulates cholesterol side chain cleavage enzyme
- Increases glucocorticoid secretion
What does Congential adrenal hyperplasia do? (CAH)
- No SRY so no testes and no AMH
- Müllerian ducts remain
- Masculinised external genitalia but androgen levels not usually high enough to full rescue Wolffian ducts
Briefly describe Congenital adrenal hyperplasia (CAH)
- Incidence rate of 1:15,000
- Completeness of the block varies
- If enzyme absent then children may be wrongly gender assigned at birth, or may have ambiguous genitalia.
- Often require treatment with glucocorticoids to correct feedback.
