Genital Physiology

Question 1

What is the genital ridge?

Answer 1

Develops from intermediate mesoderm

Genital ridges = ridge of mesenchyme + epithelium

Question 2

What is the role of PGCs?

Answer 2

PGCs migrate to genital ridges in 6th week
PGCs crucial for gonadal development - if PGCs don’t get to the genital ridges, gonads don’t develop. Primitive sex cords form.

Question 3

What are the primitive sex cords in males?

Answer 3

Primitive sex cords form the testis cords
•Testis cords continue to develop and are composed of:
•Sertoli cells (epithelial origin)
•germ cells
Leydig cells (mesenchymal origin)
•between the cords
•produce testosterone from 8/40

Question 4

What are the primitive sex cords in females?

Answer 4

Primitive sex cords regress
•Cortical cords develop
•Cortical cords divide into groups of cells that surround germ cells
•Germ cell + surrounding cells > primordial follicle

Question 5

When do gonads develop?

Answer 5

Sex determined at fertilization
•But the gonad is identical until the 7th week of development
•Two pairs of ducts: mesonephric (Wolffian) and paramesonephric (Mullerian)
•Begin to differentiate at week 7

Question 6

What occurs in male differentiation?

Answer 6

Male development
SRY = development of testes
Anti-mullerian hormone = paramesonephric (Mullerian) ducts regress
Testosterone > male differentiation, stabilization of Wolffian ducts

Question 7

What happens in female differentiation?

Answer 7

Absence of SRY
WNT4 required for ovarian development > but less well understood
Oestrogen > female differentiation, paramesonephric ducts develop

Question 8

What are the genital ducts?

Answer 8

Paramesonephric (Mullerian)
•opens into the abdominal cavity at its rostral end
•caudal ends meet in the midline
•Project into the urogenital sinus

Mesonephric (Wolffian)
•open into the urogenital sinus

Question 9

What occurs to the mesonephric ducts in males?

Answer 9

Males = ducts develop under influence of testosterone
•Form the vas deferens
•Distal end opens into urogenital sinus, is absorbed into the bladder wall so ureter and duct enter separately

Question 10

How do mesonephric ducts develop?

Answer 10

Duct opens into part that will become prostatic urethra – forms the ejaculatory duct.
•Prostate develops around the ejaculatory ducts
•Seminal vesicle develops from the vas deferens
•Sertoli cells produce anti-Mullerian hormone = paramesonephric ducts regress

Question 11

What happens to paramesonephric ducts in females?

Answer 11

Females = ducts develop under influence of oestrogen

•Upper parts > uterine tubes
•Caudal parts fuse with each other > uterus, cervix, upper vagina
•Mesonephric ducts regress

Question 12

How does the vagina develop?

Answer 12

•Upper = paramesonephric ducts
•Lower = urogenital sinus
•Paramesonephric duct meets the urogenital sinus
•Growth of the sinovaginal bulbs
•Lumen develops

Question 13

What are some uterine anomalies?

Answer 13

Duplication (didelphys)= paramesonephric ducts don’t fuse

•Bicornuate = partial fusion of paramesonephric ducts

•Unicornuate = one of the paramesonephric ducts doesn’t develop

•Septate = uterine septum doesn’t regress

Question 14

What are external genitalia like in the indifferent stage?

Answer 14

Indifferent stage - male and female embryos cannot be distinguished from each other

Question 15

How does female external genitalia develop under oestrogen?

Answer 15

Influence of oestrogen:

•Genital tubercle = clitoris
•Urethral folds = labia minora
•Urethral groove = vestibule
•Genital swellings = labia majora

Question 16

How does male external genitalia develop under DHT?

Answer 16

Influence of Dihydrotestosterone (DHT):

•Genital tubercle = elongates > penis
•Urethral folds = fuse > penile urethra
•Genital swellings = scrotum

Question 17

What is hypospadias?

Answer 17

Hypospadias
•Urethral folds do not fuse properly
•Urethral opening(s) on the ventral surface of the penis

Question 18

What is epispadias?

Answer 18

Epispadias
•Urethra opens on the dorsum of the penis
•Rare

Question 19

What causes ambiguous genitalia>?

Answer 19

External genitalia aren’t clearly or typically male or female
•Development may be characteristically male or female but with anomalies
E.g. female with large clitoris
male with small penis
•Or infant may have features of both sexes

Arise due to conditions called Disorder/ Differences of Sex Development (DSDs)

Question 20

What are some DSDs?

Answer 20

Congenital adrenal hyperplasia
Excess androgens in 46 XX individuals
Ambiguous genitalia: large clitoris, fusion of urethral folds depending on androgens

Androgen insensitivity syndrome
•46 XY individual - androgen receptor deficiency, tissues don’t respond to androgens
•Testes produce anti-Mullerian hormone > paramesonephric ducts regress (uterus does not develop)
o Partial AIS = testosterone has some effect on development. Ambiguous genitalia > apparent at birth > genetic sex determined
o Complete AIS = no testosterone. Genitalia appear female - may be undiagnosed until puberty (amenorrhea)

Question 21

WHta is the SPOILER ALERT slide??? (Vid)

Question 22

Summarise female development?

Answer 22

Absence of SRY. WNT4 key for ovarian development
•Oestrogen drives female differentiation of genitalia
•Mesonephric (Wolffian) ducts regress
•Paramesonephric (Mullerian) ducts persist and develop > uterus, uterine tubes, upper vagina
•Lower vagina develops from the urogenital sinus
•External genitalia develop as follows:
•Genital tubercle = clitoris
•Urethral folds = labia minora
•Urethral groove = vestibule
•Genital swellings = labia majora

Question 23

Summarise male development

Answer 23

SRY key for testes development
•Anti-Mullerian hormone > paramesonephric ducts degenerate
•Testosterone > male differentiation of genitalia
•Mesonephric ducts persist and develop = vas deferens
•External genitalia develop as follows:
•Genital tubercle = penis
•Urethral folds = penile urethra
•Genital swellings = scrotum