3. Development Of The Reproductive Tracts

Question 1

What common caudal opening do the reproductive tract, urinary tract and G tract share to begin with in the developing embryo?

Answer 1

Cloaca - dilated structure at the end of the hindgut.

Question 2

By what structure is the cloaca closed to the outside?

Answer 2

Cloacal membrane.

Question 3

What is the urogenital ridge?

Answer 3

Region of intermediate mesoderm that gives rise to the embryonic kidney and gonad.

Question 4

What is the gonad derived from?

Answer 4

Intermediate mesoderm plus primordial germ cells (extragonadal).

Question 5

Where do the primordial germ cells arise from?

Answer 5

The yolk sac and migrate into the retroperitoneum, along the dorsal mesentery.

Question 6

What does the expression of the SRY genes due to the primordial germ cells carrying the Y chromosome dive the development of?

Answer 6

The male gonad (testis).
Production of testicular hormones.
Internal genitalia (male duct system).

Question 7

What does the absence of the Y chromosome due to the primordial germ cells not carrying the Y chromosome, lead to the development of?

Answer 7

Female gonad (ovary).
Internal genitalia (duct system ie tubes and uterus).

Question 8

What two ducts develop in both male and female embryos, and end at the urogenital sinus part of the cloaca?

Answer 8

Mesonephric ducts and paramesonephric ducts.

Question 9

In a normal male, what happens to the paramesonephric duct and under the influence of what hormone?

Answer 9

Suppressed Müllerian duct development - so degeneration of the paramesonephric duct.
Under influence of testis producing mullerian inhibiting hormone.

Question 10

In a normal male, what happens to the mesonephric duct and under the influence of what hormone?

Answer 10

Supported wolffian duct - so mesonephric duct remains.

Testis producing androgens.

Question 11

In a normal female (or castrated male), what happens to the paramesonephric duct and under the influence of what hormone?

Answer 11

No suppression of Müllerian duct development - so paramesonephric duct remains.
No testis producing mullerian inhibiting hormone.

Question 12

In a normal female (or castrated male), what happens to the mesonephric duct and under the influence of what hormone?

Answer 12

Wolffian duct degenerates - so mesonephric duct degenerates.

No testis producing androgens.

Question 13

What is the fate of the paramesonephric and mesonephric ducts dependent on in a developing embryo?

Answer 13

Whether there is a functional testis producing mullerian inhibiting hormone and androgens.

Question 14

When may both the Wolffian and mullerian ducts develop?

Answer 14

In a female exposed to exogenous androgen. No testis so no mullerian inhibiting hormone, so Müllerian ducts develop, but then wolffian ducts also develop due to exogenous endogenous (testosterone).

Question 15

What happens to the mesonephric and paramesonephric ducts in an androgen-resistant male?

Answer 15

Receptors for testosterone don’t work, so wolffian ducts don’t develop (neither do mullerian in males).

Question 16

What is the purpose of the mesonephric duct initially?

Answer 16

Acts as the duct for the embryonic kidney (mesonephros), which drains into the urogenital sinus. The urogenital sinus later becomes the bladder.

Question 17

What happens to the mesonephric duct maintained by testis derived androgens, once the true kidney develops?

Answer 17

Converted into the vas deferens and epididymis, and migrates with the testis as it descends.

Question 18

How do the paramesonephric ducts develop?

Answer 18

Appear as invagination of the epithelium of the urogenital ridge. Make contact with the cloaca (urogenital sinus) caudally, and open into the abdominal cavity cranially.

Question 19

What do the paramesonephric form?

Answer 19

Fuse to form the uterus.

Question 20

What forms the vagina?

Answer 20

Tissue of sinovaginal bulbs from the urogenital sinus (from the hindgut).

Question 21

What are the 3 basic components of the development of the external genitalia?

Answer 21

Genital tubercle.
Genital folds.
Genital swellings.

Question 22

Describe the development of the male external genitalia, and what hormone is this under the influence of?

Answer 22

Genital tubercle elongates and genital folds fuse to form the spongy urethra. The genital tubercle develops into the glans of the penis.
Under the influence of testis-derived androgen hormones (dihydrotestosterone).

Question 23

Describe the development of the female external genitalia, and what hormone is this under the influence of?

Answer 23

No elongation of the genital tubercle and no fusion of the genital folds. Leads to development of the labia majora and labia minora. Genital tubercle develops into the clitoris and the urethra opens into the vestibule.

Question 24

What guides the descent of the testis?

Answer 24

Gubernaculum.

Question 25

Through what layers of the anterior-lateral abdominal wall do the testis invaginate on their descent, from internal to external?

Answer 25

Transversalis fascia, transversus abdominis, internal oblique, external oblique.

Question 26

What structure guides the descent of the ovary into the pelvis, and what does it attach the ovary to?

Answer 26

Gubernaculum - attaches ovary inferiorly to the labile-scrotal folds.
Also round ligament of the uterus in the inguinal canal.

Question 27

What prevents decent of the ovaries to a point further below that than they should?

Answer 27

Uterus has developed, blocking further descent.