Sexual Differentiation And Disorders

Question 1

What is sexual determination?

Answer 1

A genetically controlled process which is dependant on the Y chromosome ‘switch’

Question 2

What is sexual differentiation?

Answer 2

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

Question 3

What are the steps in sexual differentiation?

Answer 3

Genotypic sex, gonadal sex, phenotypic sex, legal sex

Question 4

What are the names of the ducts that turn into the male internal genetalia?

Answer 4

Wolffian

Question 5

What are the names of the ducts that turn into the female internal genetalia?

Answer 5

Mullarian

Question 6

What is the gonadal precursor derived from?

Answer 6

Common somatic mesenchymal tissue precursors (called genital ridge pomadia)

Question 7

Where is the genital ridge pomadia found?

Answer 7

Posterior wall of the lower thoracic lumbar region

Question 8

What are the three waves of cells that form the genital ridge?

Answer 8

Primordial germ cells, primitive sex cords and mesonephric cells

Question 9

What do the primordial germ cells differentiate into?

Answer 9

Sperm (male) or oocytes (female)

Question 10

What do the primitive sex cords differentiate into?

Answer 10

Sertoli cells (male) or granulosa cells (female)

Question 11

What do mesonephric cells differentiate into?

Answer 11

Blood vessels and leydig cells (male) or theca cells (female)

Question 12

What happens in primordial germ cell migration?

Answer 12

A small cluster of cells in the epithelium of the yolk sac expands and migrates to the connective tissue of the hindgut by 6 weeks

Question 13

How are the primitive sex cords formed?

Answer 13

Cells from the germinal epithelium that overhangs the genital ridge - the mesenchyme migrate inwards as columns

Question 14

What are the features of male primitive sex cords?

Answer 14

They express SRY, penetrate medullary mesenchyme and surround primordial germ cells to form testis cords.
Eventually become Sertoli cells which express AMH

Question 15

What are the male primitive sex cords precursors to?

Answer 15

Seminiferous tubules

Question 16

What are the features of female primitive sex cords?

Answer 16

No SRY, they condense in the cortex around the primordial germ cells (precursor to ovarian follicles)
Eventually become granulosa cells

Question 17

Where do the mesonephric cells originate?

Answer 17

Mesonephric primordium - just lateral to the genital ridges

Question 18

What do the mesonephric cells form in females?

Answer 18

Vascular tissue and theca cells

Question 19

What do the mesonephric cells form in males?

Answer 19

Vascular tissues, leydig cells, basement membrane

Question 20

What do leydig cells do?

Answer 20

Synthesise testosterone and don’t express SRY

Question 21

What does the basement membrane in males contribute to?

Answer 21

Formation of seminiferous tubules and rete-testis

Question 22

What inhibits mullarian duct Development in males?

Answer 22

AMH (anti-mullarian hormone)

Question 23

What do Mullerian ducts form in females?

Answer 23

Uterine tubes, the uterus and part of the vagina

Question 24

What inhibits wolffian duct development in females?

Answer 24

Lack of testosterone stimulation

Question 25

What do the wolffian ducts form in males?

Answer 25

Epididymis and vas deferens

Question 26

What enzyme converts testosterone into dihydrotestosterone?

Answer 26

5-alpha reductase

Question 27

Why is testosterone converted into dihydrotestosterone?

Answer 27

It’s much more potent

Question 28

What does dihydrotestosterone cause?

Answer 28

Differentiation of the male external genetalia:

• clitoral area enlarges into penis
• labia fuse and become ruggated to form scrotum and the prostate forms

Question 29

What is gonadal dysgenesis?

Answer 29

Sexual differentiation is incomplete

Question 30

What causes gonadal dysgenesis?

Answer 30

Missing SRY in male or partial or complete loss of the second X chromosome in females

Question 31

What does intersex mean?

Answer 31

Have some components of both tracts or ambiguous genetalia

Question 32

What are the symptoms of androgen insensitivity syndrome?

Answer 32

Testes form and make AMH so the mullarian ducts regress, but there’s no differentiation of the wolffian ducts - means female or ambiguous external genetalia

Question 33

What is the phenotype in complete androgen insensitivity syndrome?

Answer 33

Completely female - due to undescended testes

Question 34

How do you diagnose complete androgen insensitivity syndrome?

Answer 34

Primary amenorrhoea/ lack of body hair

Ultrasound and karyotype

Question 35

What is the phenotype of partial androgen insensitivity syndrome?

Answer 35

Varying degrees of penile and scrotal development from ambiguous genetalia to a large clitoris

Question 36

What is the external phenotype in 5-alpha reductase deficiency?

Answer 36

Feminine or ambiguous external genetalia

Question 37

What is the internal phenotype in 5-alpha reductase deficiency?

Answer 37

Undescended testes, but no dihydrotestosterone so no penile or scrotal formation

Question 38

Do patients with a 5-alpha reductase deficiency have wolffian or mullarian ducts?

Answer 38

Wolffian ducts

Question 39

What may happen at puberty in patients with a 5-alpha reductase deficiency?

Answer 39

High testosterone levels may induce virilisation

Question 40

What causes Turner syndrome?

Answer 40

No Y chromosome or second X chromosome

Question 41

What is the phenotype of a patient with Turner syndrome (internal and external)?

Answer 41

Ovaries, mullarian ducts, female external genetalia

Question 42

What are the symptoms of Turner’s syndrome?

Answer 42

Failure of ovarian function (may be fertile - mosaicism)
Uterus and uterine tubes are present but small
May have brittle bones (hormones support bone formation/ maturation)

Question 43

What is the phenotype of congenital adrenal hyperplasia?

Answer 43

Masculinised external genetalia but female internal genetalia