S2) Development of the Reproductive Tracts

Question 1

Describe the relationship between the primordial germ cells and the gonad in the embryology of the reproductive system

Answer 1

• Primordial germ cells migrate into an indifferent gonad
• The primordial germ cells carry the karyotype for the organism

Question 2

Describe the differentiation of the gonad into testis / ovary and the resulting duct systems

Answer 2

• Gonad can develop into testis (XY) or ovary (XX)
• Testis then develop duct systems: epididymis & vas deferens
• Ovary then develops duct systems: uterus, tubes & part of vagina

Question 3

The development of the reproductive tract, urinary tract and GI tract are closely linked.

Illustrate this

Answer 3

• All three systems share common caudal opening
• Hindgut ends in dilated structure (cloaca)
• Closed to the outside by cloacal membrane (no mesoderm

Question 4

What is urogenital ridge?

Answer 4

Urogenital ridge is a region of intermediate mesoderm giving rise to both the embryonic kidney and the gonad

Question 5

What is the gonad derived from?

Answer 5

Gonad (indifferent) derived from intermediate mesoderm plus primordial germ cells (extragonadal)

Question 6

What are primordial germ cells?

Answer 6

• Special population
• “Seed” for the next generation, allocated shortly after initiation of the current generation

Question 7

What are the origins and location of primordial germ cells?

Answer 7

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

Question 8

What features are associated when a gonad develops into the testes?

Answer 8

• Medullary cords develop
• No cortical cords
• Thick tunica albuginea

Question 9

What features are associated when a gonad develops into the ovaries?

Answer 9

• Medullary cords degenerate
• Cortical cords develop
• No tunica albuginea

Question 10

Explain how the expression of SRY genes drives development of male

Answer 10

• Gonad (testis)
• Production of testicular hormones
• Internal genitalia (male duct system)

Question 11

Explain how the absence of Y chromosome leads to development of female

Answer 11

• Gonad (ovary)
• Internal genitalia (duct system – i.e. tubes & uterus)

Question 12

Identify the pair of ducts involved in the indifferent stage of the development of internal genitalia, as well as their location

Answer 12

• Mesonephric ducts and paramesonephric ducts develop in both male and female embryos
• Both ducts end at the urogenital sinus part of the cloaca

Question 13

What are other names for the paramesonephric and mesonephric ducts?

Answer 13

• Paramesonephric = Mullerian duct
• Mesonephric = Wolffian duct

Question 14

Describe the fate of the paramesonephric and mesonephric ducts in a normal male

Answer 14

When there is a functional testis:

• Testis produces Mullerian inhibiting hormone which suppresses Mullerian duct development
• Testis produces androgens which supports Wolffian duct

Question 15

Describe the fate of the paramesonephric and mesonephric ducts in a normal female

Answer 15

When there is not a functional testis:

• No suppression of Mullerian duct development (no Mullerian inhibiting hormone)
• Wolffian duct degenerates (no testes androgens)

Question 16

What happens when the fate of the ducts go wrong and there is no testis?

Answer 16

• Exogenous androgen: supports Wolffian duct
• No Mullerian inhibiting hormone: Mullerian ducts develop (no testes)

Question 17

What happens when the fate of the ducts go wrong and there is Androgen Insensitivity Syndrome?

Answer 17

• Testosterone receptors don’t work: Wolffian ducts degenerate
• MIH present: Mullerian ducts degenerate

Question 18

Outline the development of the Wolffian duct

Answer 18

• Acts as duct for the embryonic kidney
• Drains into the urogenital sinus
• Surplus to requirement once true kidney develops

Question 19

Describe the maintenance, conversion and migration of the mesonephric duct

Answer 19

• Maintained by testis-derived androgens
• Converted into the vas deferens and epididymis
• Migrates with the testis as it descends

Question 20

Describe the caudal and cranial development of the paramesonephric ducts

Answer 20

Paramesonephric ducts appear as invaginations of the epithelium of the urogential ridge

• Caudally: make contact with the cloaca (urogenital sinus)
• Cranially: open into the abdominal cavity

Question 21

Describe the features of the external genitalia at the indifferent stage of development

Answer 21

Basic components:

• Genital tubercle (GT)
• Genital folds
• Genital swellings

Question 22

Outline the development of the external genitalia in males

Answer 22

• In the male the GT elongates and develops into glans of penis
• Genital folds fuse to form the spongy urethra
• Influence of testis-derived androgen hormones – dihydrotestosterone

Question 23

Outline the development of the external genitalia in females

Answer 23

• No fusion: development of labia majora & minora
• GT develops into clitoris
• Urethra opens into the vestibule

Question 24

Describe the descent of the testes

Answer 24

• The testes descend under the guidance of the gubernaculum testis, into the scrotum
• Originally located in peritoneum
• Tunica vaginalis is a remnant of infolded peritoneum

Question 25

Describe the descent of the ovaries

Answer 25

• Gubernaculum attaches ovary inferiorly to labio-scrotal folds
• Ovary descends to the pelvis
• Uterus has developed (prevents further descent)

Question 26

What is the adult derivative of the urogenital sinus?

Answer 26

Urogenital sinus becomes urinary bladder