Sexual differentiation

Question 0

What is sexual DIFFERENTIATION?

Answer 0

Process by which internal and external genitalia develop as male or female to give phenotype

Question 1

What is sexual DETERMINATION?

Answer 1

Genetically controlled process that is dependent on the ‘switch’ on the Y chromosome

Question 2

Sexual differentiation steps

Answer 2

Fertilisation –> genotypic sex –> gonadal sex –> phenotypic sex –> legal sex –> gender identity

Question 3

What is the SRY?

Answer 3

Sex determining region Y

Question 4

What does the SRY do?

Answer 4

It switches on briefly around 7 weeks to make gonads into testes

Question 5

Production of testes drives…

Answer 5

1. Differentiation of germ cells into sperm stem cells
2. Development of internal organs
3. Development of external appearance

Question 6

What are the main two structures of sexual differentiation of the internal organs?

Answer 6

1. Müllerian ducts

2. Wolffian ducts

Question 7

Müllerian ducts

Answer 7

Most important in females

Inhibited in males

Question 8

Wolffian ducts

Answer 8

Most important in males

Lack of stimulation causes regression in females

Question 9

Initial steps of male sexual differentiation

Answer 9

1. Testes develop in response to SRY

2. Testes rapidly develop cells that make Sertoli and Leydig cells.

Question 10

What do Sertoli cells make?

Answer 10

Anti-Mullerian hormone (AMH)

Question 11

What do Leydig cells make?

Answer 11

Testosterone

Question 12

How does sexual differentiation occur in males?

Answer 12

1. Anti-Müllerian hormone inhibits the Müllerian ducts
2. Wolffian ducts form urinary tract in both sexes
3. Under testosterone Wolffian ducts then forms:
   Body and tail of epididymis
   Vas deferens
   Seminal vesicles
   Ejaculatory ducts

Question 13

Male external differentiation

Answer 13

• Testosterone is converted into DHT (Dihydrotestosterone) by 5a reductase
• DHT causes differentiation

Question 14

How does DHT cause male differentiation?

Answer 14

Area around and including clitoris enlarges into penis.
Labia fuse and becomes nuggated –> scrotum
Prostate forms

Question 15

Internal sexual differentiation in female

Answer 15

No Y chromosome therefore no SRY so no testes
No testes = no anti-Müllerian hormone
Therefore no inhibition of Müllerian ducts

Question 16

What do the Müllerian ducts do in internal sexual differentiation?

Answer 16

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

Question 17

External differentiations caused by DHT?

Answer 17

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

Question 18

What happens when sexual differentiation goes wrong?

Answer 18

• Gonadal dysgenesis
• Sex reversal
• Intersex

Question 19

Define gonadal dysgenesis

Answer 19

When sexual differentiation is incomplete;

• missing SRY in males
• partial/complete deletion of second X in female

Question 20

Define sex reversal

Answer 20

When the phenotype doesn’t match the genotype

I.e maybe be male genotypically but externally look female

Question 21

Define intersex

Answer 21

When they have some components of both tracts or have continuos genitalia (sex of child difficult to determine)