Embryology

Question 1

From what does the urogenital tract develop? (2)

Answer 1

Intermediate mesoderm - urogenital ridge.

Question 2

Describe how to make a reproductive system that is gender specific. (14)

Answer 2

The primordial germ cells create an indifferent gonad.
With XY (SRY gene on the Y) they differentiate into testes which release testosterone. With XX they don’t, forming ovaries, which don’t release testosterone.
With this hormone release, the indifferent duct system forms the epididymis and Vas Deferens from persistence of the Wolffian Duct and degeneration of the Müllerian duct due to Müllerian inhibiting hormone. Without this hormone release, the indifferent duct system forms the uterus, tubes and vagina, from degeneration of the Wolffian duct and persistence of the Müllerian duct due to no MIH.
The hormones also prompt the indifferent external genitalia to form a penis, and an absence of these will not form a penis, so will form the vulva etc.

Question 3

Describe what would happen in a female with excess testosterone. (3)

Answer 3

Wolffian duct persistence, but no MIH, both ducts persist.

Question 4

Describe what would happen in androgen insensitivity syndrome. (3)

Answer 4

Testosterone still produced but unrecognised, so Wolffian ducts degenerate. MIH still produced, so Müllerian ducts degenerate also, no ducts.

Question 5

Describe the genitals of a 7 week old foetus. (7)

Answer 5

Indistinguishable between genders.

Genital tubercle, genital folds, genital swellings, urogenital sinuses and anus.

Question 6

Describe how a penis forms. (3)

Answer 6

Genital tubercle elongates and becomes glans penis, the genital folds fuse to form the penis and penile urethra. Genital swellings fuse to form the scrotum.

Question 7

Describe how the vulva etc form. (2)

Answer 7

No fusion of the genital swellings occurs, so they become the vulva. Genital tubercle becomes the clitoris.