Embryology of the Reproductive Tract

Question 1

What does gastrulation lead to?

Answer 1

Formation of the trilaminar disc

Question 2

What occurs in gastrulation?

Answer 2

Invagination of the epiblast cells through the primitive streak to form the definitive endoderm and mesoderm

Question 3

How is the mesoderm organised?

Answer 3

Into 3 main groups = paraxial, intermediate and lateral plate

Question 4

What is special about the urogenital system?

Answer 4

Made from two functionally distinct systems which are developmentally and anatomically interwoven

Question 5

What do the urinary and genital systems arise from?

Answer 5

The intermediate mesoderm

Question 6

Where do the excretory ducts of the urogenital system enter?

Answer 6

A common cavity called the cloaca

Question 7

What happens to the primordial germ cells in weeks 4-6?

Answer 7

Primordial germ cells within the yolk sac migrate via dorsal mesentery to the intermediate mesoderm

Question 8

How are the genital ridges formed?

Answer 8

From the proliferation and thickening of the coelomic epithelium

Question 9

How are the primitive sex cords formed?

Answer 9

The proliferating coelomic epithelium forms somatic support cells which envelop primordial germ cells

Question 10

What happens in the bipotential phase?

Answer 10

Development of the genital ducts = mesonephric (Wolffian) and paramesonephric (Mullerian) ducts

Question 11

Where do both genital ducts connect to?

Answer 11

The posterior wall of the urogenital sinus

Question 12

What makes up the bipotential phase?

Answer 12

Genital ducts and indifferent gonads

Question 13

When does sexual differentiation occur?

Answer 13

From week 7 onwards

Question 14

What triggers development of the male genital system?

Answer 14

Presence of SRY transcription factor

Question 15

What do somatic support cells develop into in males?

Answer 15

Sertoli cells

Question 16

What do the primary sex cords form in males?

Answer 16

Testis/medullary cords = engulf the primordial germ cells

Question 17

What do the rete testis connect?

Answer 17

The mesonephric tubules to the testis cords

Question 18

What is the tunica albuginea?

Answer 18

Thickened layer of connective tissue between the coelomic epithelium and testis cords

Question 19

What do sertoli cells secrete?

Answer 19

Anti-Mullerian hormone = causes degeneration of the paramesonephric (Mullerian) duct

Question 20

What stimulates gonadal ridge cells to form leydig cells?

Answer 20

Sertoli cells

Question 21

What do leydig cells produce?

Answer 21

Testosterone = induces formation of epididymis, vas deferens and seminal vesicle

Question 22

What does dihydrotestosterone induce?

Answer 22

Development of male specific external genitalia and prostate

Question 23

What causes persistent Mullerian duct syndrome?

Answer 23

Mutations of AMH or AMH receptor genes = Mullerian ducts fail to regress

Question 24

How does persistent Mullerian duct syndrome present?

Answer 24

Present with uterus, vagina and uterine tubes
Testes are in ovarian location
Have male external genitalia

Question 25

Where do the testes originate before they descend?

Answer 25

Originate at 10th thoracic level and are pulled caudally by the gubernaculum

Question 26

What is cryptorchidism?

Answer 26

Failure of one or both testes to descend

Question 27

What causes development of female genital system?

Answer 27

Absence of SRY transcription factor

Question 28

What do germ cells differentiate into in females?

Answer 28

Oogonia and then into primary oocytes

Question 29

What do somatic support cells differentiation into in females?

Answer 29

Granulosa cells which then go on to surround the primary oocytes = forms primordial follicles and thecal cells

Question 30

What forms the primordial follicles and thecal cells?

Answer 30

Female gonad

Question 31

What do influences of the ovarian oestrogens and from maternal sources stimulate?

Answer 31

Formation of the female external genitalia and development of the paramesonephric (Wolffian) ducts

Question 32

What do the Mullerian ducts give rise to in females?

Answer 32

Uterine tubes, uterus and superior vagina

Question 33

What are the three parts of the Mullerian duct?

Answer 33

Cranial portion = opens into coelomic cavity Horizontal portion = crosses mesonephric duct Caudal portion = fuses with Mullerian duct on opposite side

Question 34

What forms the uterovaginal canal?

Answer 34

Fused caudal portion of the Mullerian ducts = gives rise to uterus and superior vagina

Question 35

How is the vaginal lumen created?

Answer 35

By vacuolisation of the Mullerian portion of the vagina and the sinuvaginal bulbs = produces the fornices

Question 36

What are some abnormalities of the female genital system?

Answer 36

Double uterus and double vagina Double uterus, bicornate uterus or septated uterus Unicornate uterus or cervical atresia

Question 37

What is the indifferent stage of external genitalia development?

Answer 37

Between week 4-7 the external genitalia are indistinguishable

Question 38

How does the spongy urethral form?

Answer 38

By proximal to distal zipping of urethral groove

Question 39

What is present at the tip of the glans?

Answer 39

Ectodermal ingrowth which meets the spongy urethra

Question 40

How is the foreskin formed?

Answer 40

By circular ingrowth of ectoderm around the periphery of the glans = occurs in week 12

Question 41

What is hypospadias?

Answer 41

External urethral opening lies in abnormal position along ventral aspect of penis = occurs with varying degrees of severity