Session 2: Development of the Reproductive Tracts

Question 1

From which of the three germ layers do the reproductive tracts arise primarily from?

Answer 1

The intermediate mesoderm.

Question 2

Embryonic folding gives rise to the gut tube which can be separated into the foregut, midgut and hindgut. Which is an important anatomical location in the creation of the reproductive and urinary tracts?

Answer 2

The hindgut.

Question 3

What does the hindgut give rise to?

Answer 3

A single opening called the cloaca which will become the urogenital sinus.

Question 4

What is the urogenital sinus?

Answer 4

The common opening for the reproductive and urinary systems.

Question 5

What is the urogenital ridge?

Answer 5

An important region which can be found in the posterior abdominal wall which will give rise to the embryonic kidney (mesonephros) and the gonads with the mesonephric duct.

Question 6

What are the gonad derived from?

Answer 6

From intermediate mesoderm and primordial germ cells.

Question 7

What are the primordial germ cells?

Answer 7

They are a specialised population of cells that arise from the yolk sac.

Question 8

What will the primordial germ cells do?

Answer 8

They will produce sperm or ova.

Question 9

What determines the differentiation of the gonads?

Answer 9

It depends on the sex chromosomes. Whether the embryo has XY or XX.
In case of XY it will have a gene called SRY where the encoding to differentiate into a testis, seminiferous tubules and primordial germ cell (remain), can be found.

In the absence of the Y chromosome, ovaries will be formed instead. The primordial germ cells will form into primordial follicles.

Question 10

Difference in differentiation once XX and XY has been encoded.

Answer 10

Testis will form in XY with medullary cords developing, and without any cortical cords.

Ovaries will develop in absence of Y chromosome with medullary cords degenerating and cortical cords developing.

Question 11

What else does the SRY gene drive?

Answer 11

The production of testicular hormones (via the testis)

Question 12

There are two ducts in the embryonic development of the urinary and reproductive systems. Which?

Answer 12

The mesonephric duct and the paramesonephric duct.

Question 13

What will happen to the mesonephric duct and the paramesonephric duct in males?

Answer 13

The mesonephric duct will persist and become the vas deferens and epididymis whereas the paramesonephric duct will degenerate.

Question 14

What causes the mesonephric duct to persist in males?

Answer 14

Androgen released from testis maintains the mesonephric duct.

Question 15

What causes the paramesonephric duct to degenerate in males?

Answer 15

The testes release MIH aka Mullerian inhibiting hormone. This causes the paramesonephric duct to degenerate.

Question 16

Another name fo the mesonephric and paramesonephric ducts.

Answer 16

Wolffian and Mullerian ducts respectively.

Question 17

Where do the Wollfian and Mullerian ducts end?

Answer 17

At the urogenital sinus part of the cloaca.

Question 18

What will happen to the Wollfian and Mullerian ducts in females?

Answer 18

The Wolffian duct will degenerate and the Mullerian duct will persist to then form the uterus, the uterine tube and parts of the vagina.

Question 19

What causes the Wollfian duct to degenerate in women?

Answer 19

Since women don’t have testes they won’t produce any androgen. The absence of androgen causes the Wollfian duct to degenerate.

Question 20

What causes the Mullerian duct to persist in women?

Answer 20

Since women don’t have testes they won’t produce any MIH. The absence of MIH causes the Mullerian duct to persist.

Question 21

How do the mesonephric ducts fuse?

Answer 21

They fuse with the testes which means they will be continuous and not open into the peritoneum.

Question 22

Explain the paramesonephric ducts development and its clinical significance in adulthood.

Answer 22

The Mullerian ducts appear as invaginations of the epithelium of the urogenital ridge. Caudally the make contact with the cloaca but cranially they open into the abdominal cavity.

This persists in adulthood since there is no direct connection between the ovaries and the Mullerian duct (fallopian tube) in adults.

Question 23

What can have happened if a female has both Wolffian and Mullerian ducts?

Answer 23

They might have exogenous androgen supporting the Wolffian duct and no MIH since they don’t have testes to produce it to degenerate the Mullerian duct.

Question 24

What is androgen insensitivity syndrome?

Answer 24

Receptors for testosterone don’t work so the Wollfian ducts don’t survive.
MIH is still present due to testes so Mullerian ducts also degenerate.

Question 25

Basic components of the external genitalia.

Answer 25

Genital tubercle Genital folds Genital swellings They can all be found in both males and females.

Question 26

What happens to the basic components of the external genitalia in males? Why does it happen?

Answer 26

It is influenced by testis derived androgen hormones like dihydrotestosterone. The genital tubercle elongates and the genital folds fuse to form the spongy urethra. Genital tubercle then develops into glans penis. The genital swelling becomes the scrotum.

Question 27

What happens to the basic components of the external genitalia in females?

Answer 27

There is no fusion occuring in males. Genital tubercle develops into the clitoris. Genital folds become part of the labia minora Genital swelling becomes the labia majora.

Question 28

Briefly explain the descent of the testis.

Answer 28

Gubernaculum attaches the gonad inferiorly to the labio-scrotal folds. When the abdominopelvic cavity increases in volume the gonad will start to descend inferiorly. The gubernaculum will descend past the pubic symphysis along with the scrotal swelling. It will pull the testis with it and descend inferior to the pubic symphysis along with the processus vaginalis which is a continuation of the peritoneum. The connection between the peritoneal cavity and the testes (processus vaginalis) will then close and a remnant of the peritoneum will be closed off to the peritoneal cavity and is now called the tunica vaginalis.

Question 29

Complications of the processus vaginalis not closing.

Answer 29

This can cause hydrocoele, haematocoele. It can also lead to indirect inguinal hernias.

Question 30

Briefly explain the descent of the ovary.

Answer 30

Gubernaculum attaches to the ovary inferiorly to the labio-scrotal folds. The ovary then descends to the pelvis but since the uterus has developed by now it is stopped and the uterus prevents any further descent. The remnants of the gubernaculum becomes the ovarian ligament and the round ligament.