Development of the reproductive tracts

Question 1

When does embryonic development occur?

Answer 1

4th week

Question 2

Which embryonic layer gives rise to the urogenital tract?

Answer 2

intermediate mesoderm

Question 3

What decides if the foetus is male or female?

Answer 3

Karyotype (if there is a Y chromosome). This decides the path taken for development.

Question 4

What is the common origin of the urinary, GI and reproductive tract?

Answer 4

Cloaca - this is a dilated structure at the end of the hindgut

Question 5

What is the urogenital ridge?

Answer 5

Region on intermediate mesoderm giving rise to both embryonic kidneys and gonads

Question 6

What is the gonad derived from?

Answer 6

Intermediate mesoderm and primordial germ cells.

Question 7

How do the primordial germ cells arise?

Answer 7

Arise from the yolk sac and migrate into the retroperitoneum, along the dorsal mesentery

Question 8

What is the differences between the development of the gonads with / without a Y?

Answer 8

With a Y = Testes

• Medullary cord develops
• No cortical cords
• Thick tunica albuginea

Without a Y = Ovary

• Medullary cord degenerates
• Cortical cord develops
• No tunica albuginea

Question 9

Why does the Y chromosome make males male?

Answer 9

Because of the expression of the SRY gene. 
This causes development of the:
-Testes
-Testicular hormones 
-Internal genitalia

Question 10

What happens in X chromosome gametes?

Answer 10

Absence of Y chromosome leads to female development.

• Gonad (ovary)
• Internal genitalia - duct system

Question 11

What are the mesonephric ducts?

Answer 11

Ducts that develop the embryonic kidney

Question 12

Where do the mesonephric and paramesonephric ducts end?

Answer 12

Urogenital sinus part as of the cloaca

Question 13

What hormones do the males produce and what effect do these have?

Answer 13

Mullerian inhibiting hormone - suppress malarian (paramesonephric) duct development
Androgens - supporting Wolffian (mesonephric) duct

Question 14

What happens if the males hormones are not produced?

Answer 14

No testes producing Mullerian inhibiting hormone - so no suppression of Mullerian / Paramesonephric duct development
No testes producing androgens - Wolffian (mesonephric) duct degenerates

Question 15

What happens if exogenous androgen but no testes?

Answer 15

Exogenous androgen supports mesonephric duct formation but, no testis so no MIH so, the paramesonephric duct also develops. (So person has both ducts)

Question 16

What happens if AIS?

Answer 16

AIS = androgen insensitivity syndrome

• Receptors for testosterone won’t work so the Wolffian ducts dont survive and the MIH is present so Mullerian ducts degenerate.
• This means that neither duct develops.

Question 17

Where does the mesonephric duct drain?

Answer 17

Into urogenital sinus which becomes the bladder

Question 18

What does the mesonephric duct turn into?

Answer 18

Vas deferens and epidydimis

It migrates and descends.

Question 19

What do the paramesonephric ducts form?

Answer 19

The two paramesonephric ducts meet in the midline and fuse at the urogenital sinus to form the uterus

Question 20

What happens to the redundant paramesonephric duct? Why?

Answer 20

It degenerates because the testes secrete MIH. This occurs in XY embryo. In these people, androgen secretion also supports the mesonephric duct.

Question 21

What happens to the redundant mesonephric duct? Why?

Answer 21

It degenerates because no androgens are produced as there are no testes. This occurs in XX embryos and also means that there is no MIH and ovaries develop.

Question 22

What are the basic components of the external genetalia?

Answer 22

Genital tubercle
Genital folds
Genital folds

Question 23

How does the male external genitalia develop?

Answer 23

GT elongates and genital folds fuse under influence of dihydrotestosterone to form the spongy urethra. This then becomes the glans penis

Question 24

How does the female external genitalia develop?

Answer 24

No fusion of the genital folds - remain open so development of the labia majora and minors.
Genital tubercle develops into clitoris.
Urethra opens into vestibule.

Question 25

Where does the gubernaculum attach?

Answer 25

Inferiorly to the labio-scrotal folds as the abdominopelvic cavity increases in volume.
Gonads then begin its descent inferiorly.

Question 26

Where is the testes?

Answer 26

Retroperitoneal!

Question 27

Why does the spermatic cord have coverings derived from abdominal wall?

Answer 27

Because testes pushes through and picked up layers from anatomical wall.
Layers:
External oblique muscle
Internal oblique muscle
Transversus abdominis muscle
Transversalis fascia
Extraperitoneal fascia
Parietal peritoneum

Question 28

Where does the ovary descent?

Answer 28

Gubernaculum attaches ovary inferiorly to labio-scrotal folds.
Ovary descends to pelvis.

Question 29

Why does the ovary not descend like the testes?

Answer 29

Because uterus and fallopian tubes are in the way.

Question 30

What is in the female inguinal canal?

Answer 30

Round ligament.