Sexual differentiation Flashcards
What is sexual DIFFERENTIATION?
Process by which internal and external genitalia develop as male or female to give phenotype
What is sexual DETERMINATION?
Genetically controlled process that is dependent on the ‘switch’ on the Y chromosome
Sexual differentiation steps
Fertilisation –> genotypic sex –> gonadal sex –> phenotypic sex –> legal sex –> gender identity
What is the SRY?
Sex determining region Y
What does the SRY do?
It switches on briefly around 7 weeks to make gonads into testes
Production of testes drives…
- Differentiation of germ cells into sperm stem cells
- Development of internal organs
- Development of external appearance
What are the main two structures of sexual differentiation of the internal organs?
- Müllerian ducts
2. Wolffian ducts
Müllerian ducts
Most important in females
Inhibited in males
Wolffian ducts
Most important in males
Lack of stimulation causes regression in females
Initial steps of male sexual differentiation
- Testes develop in response to SRY
2. Testes rapidly develop cells that make Sertoli and Leydig cells.
What do Sertoli cells make?
Anti-Mullerian hormone (AMH)
What do Leydig cells make?
Testosterone
How does sexual differentiation occur in males?
- Anti-Müllerian hormone inhibits the Müllerian ducts
- Wolffian ducts form urinary tract in both sexes
- Under testosterone Wolffian ducts then forms:
Body and tail of epididymis
Vas deferens
Seminal vesicles
Ejaculatory ducts
Male external differentiation
- Testosterone is converted into DHT (Dihydrotestosterone) by 5a reductase
- DHT causes differentiation
How does DHT cause male differentiation?
Area around and including clitoris enlarges into penis.
Labia fuse and becomes nuggated –> scrotum
Prostate forms
Internal sexual differentiation in female
No Y chromosome therefore no SRY so no testes
No testes = no anti-Müllerian hormone
Therefore no inhibition of Müllerian ducts
What do the Müllerian ducts do in internal sexual differentiation?
Uterine tubes, uterus and upper 1/3 of vagina form
- upper ends of ducts stay open and form end of uterine tubes
- lower portions fuse to form single cavity uterus
External differentiations caused by DHT?
Male:
Testosterone converted to DHT to form penis, scrotum and prostate
Female:
Absence of DHT allows clitoris, labia and lower 2/3 vagina to form
What happens when sexual differentiation goes wrong?
- Gonadal dysgenesis
- Sex reversal
- Intersex
Define gonadal dysgenesis
When sexual differentiation is incomplete;
- missing SRY in males
- partial/complete deletion of second X in female
Define sex reversal
When the phenotype doesn’t match the genotype
I.e maybe be male genotypically but externally look female
Define intersex
When they have some components of both tracts or have continuos genitalia (sex of child difficult to determine)
