Development of the Genital Ducts and External Genitalia

Question 1

What is significant about the first 13 weeks in development?

Answer 1

It is difficult to determine the sex of a baby from their external genitalia

Question 2

What is the reproductive system derived from?

Answer 2

Intermediate mesoderm

This forms the urogenital ridge

Question 3

What develops from the urogenital ridge?

Answer 3

1. urinary system

2. reproductive system

Question 4

What are primitive sex cords and what are they derived from?

Answer 4

Thickened epithelium (derived from mesoderm) of the genital ridge produces primitive sex cords

The primitive sex cords migrate into the underlying mesenchyme

Question 5

What is the alternative name for primitive sex cords?

Answer 5

Medullary cords

Question 6

What is significant about primordial germ cells?

Answer 6

They migrate from the yolk sac and contain the autosomes that will determine male or female development

Question 7

In the presence of primordial germ cells carrying XY chromosomes, what happens to the primitive sex cords?

Answer 7

The somatic support cells in the medullary cords differentiate into Sertoli cells

Question 8

What will the Sertoli cells go on to form?

Answer 8

The primordial germ cells are invested by the Sertoli cells to form testes cords

These are solid cords

Question 9

What do the testes cords go on to form?

Answer 9

The testes cords develop further and separate from the overlying epithelium to form seminiferous tubules

Question 10

What happens to the seminiferous tubules at puberty?

Answer 10

They are solid until puberty

At puberty they recanalise, allowing the male to produce sperm

Question 11

How does TDF influence the male gonadal development?

Answer 11

TDF maintains the medullary cords

Question 12

How do the primordial germ cells influence female gonadal development?

Answer 12

The PGCs migrate to the posterior wall and stimulate breakdown of the medullary cords

Cortical cords develop

Question 13

What do the cortical cords go on to form?

Answer 13

The somatic support cells in the cortical cords invest the PGCs

This leads to formation of primordial follicles

Question 14

What duct system remains in male development?

Answer 14

TDF maintains the mesonephric ducts

The paramesonephric duct is broken down

Question 15

What duct system remains in female development?

Answer 15

Absence of TDF causes the mesonephric duct to break down

The paramesonephric duct continues to develop

Question 16

What are the alternative names for the mesonephric and the paramesonephric ducts?

Answer 16

The paramesonephric duct system is the Müllerian system

The mesonephric duct system is the Wolffian system

Question 17

What encodes TDF and drives development of male genital ducts?

Answer 17

The SRY gene encodes for TDF

This is testis determining factor (TDF)

Question 18

What happens after the somatic support cells invest the PGCs and differentiate into Sertoli cells?

Answer 18

Sertoli cells secrete anti-müllerian hormone (AMH)

Question 19

What is the role of anti-müllerian hormone (AMH)?

Answer 19

It actively causes the breakdown of the paramesonephric (Müllerian) ducts

Question 20

How do the Sertoli cells affect the underlying mesenchyme of the gonad?

Answer 20

They cause differentiation of the mesenchyme into Leydig cells

Question 21

What is the role of Leydig cells?

Answer 21

They produce testosterone

This promotes maintenance and further development of mesonephric ducts

Question 22

What 4 structures will the mesonephric duct develop into?

Answer 22

1. efferent ductules
2. epididymis
3. vas deferens
4. seminal vesicle

Question 23

What is formed from the remnants of the paramesonephric duct in males?

Answer 23

1. appendix testis

2. utriculus prostaticus

Question 24

Why do the paramesonephric ducts develop in females?

Answer 24

There is no anti-müllerian hormone

The paramesonephric ducts remain

Question 25

What happens to the mesonephric duct system in females and why?

Answer 25

The mesonephric ducts degenerate as there is no testosterone to maintain them

Question 26

How is the uterine canal (uterus) formed from the paramesonephric duct system?

Answer 26

The caudal tips of the duct system fuse together to form the uterine canal

Question 27

What are the 3 parts of the paramesonephric duct and what do they form?

Answer 27

1. cranial 2. horizontal 3. caudal Cranial and horizontal parts become the uterine tubes Caudal parts fuse to form the uterine canal

Question 28

What structures are formed from the remnants of the mesonephric duct in females?

Answer 28

1. Epoophoron 2. Paraoophoron 3. Gartner's cyst

Question 29

Once the caudal tips of the paramesonephric duct system fuse together, what must happen?

Answer 29

The uterine septum between them must break down to form a single uterine cavity

Question 30

How does the cloaca divide? What are the 2 parts formed?

Answer 30

The urorectal septum continues to develop to separate the cranial and caudal parts of the cloaca Cranial part - urogenital sinus Caudal part - anorectal canal

Question 31

What are the sinovaginal bulbs and where do they develop from?

Answer 31

The sinovaginal bulbs are a thickening of endoderm from the urogenital sinus

Question 32

How does the vagina form?

Answer 32

The sinovaginal bulbs fuse with the caudal tips of the paramesonephric ducts to form the vagina

Question 33

What are the 2 origins of the vagina?

Answer 33

1. the distal part of the vaginal canal is formed from the sinovaginal bulbs (endoderm) 2. the upper vaginal canal is formed from paramesonephric ducts (mesoderm)

Question 34

What can cause double uterus and double vagina?

Answer 34

Failure of caudal tips of paramesonephric ducts to fuse together

Question 35

What causes double uterus? | but only one vagina

Answer 35

The paramesonephric ducts do fuse, but only at the very tip

Question 36

What causes bicornate uterus?

Answer 36

The paramesonephric ducts have fused, but slightly in the wrong location

Question 37

What causes cervical atresia? What is this?

Answer 37

The caudal tips of the paramesonephric ducts only just meet This leads to the cervix being very thin

Question 38

What causes unicornate uterus?

Answer 38

Only one paramesonephric duct doesn't develop properly This leads to only one uterine tube being present

Question 39

What is septated uterus and what causes it?

Answer 39

The septum between the 2 paramesonephric ducts may break down

Question 40

What % of fertile women are affected by abnormalities of the uterus? What are the risks associated with this?

Answer 40

1% This leads to higher rates of: 1. miscarriage 2. premature delivery 3. dystocia (difficult birth)

Question 41

What causes persistent müllerian duct syndrome?

Answer 41

A mutation in the AMH gene This means there is no anti-müllerian hormone so the paramesonephric ducts persist

Question 42

What is involved in persistent müllerian duct syndrome?

Answer 42

Both mesonephric and paramesonephric duct derivatives develop There are developing testes, but a uterus also develops

Question 43

What are the genitalia like in persistent müllerian duct syndrome?

Answer 43

There is normal male genitalia but it is associated with cryptorchidism

Question 44

What is the indifferent stage in development of the external genitalia?

Answer 44

Up until 13 weeks in development, the male and female external genitalia is almost the same

Question 45

What is the first stage in development of the external genitalia?

Answer 45

Mesoderm cells migrate to surround the cloacal membrane They form elevations called cloacal folds

Question 46

What do the cloacal folds go on to form?

Answer 46

Cloacal folds unite anteriorly to form the genital tubercle This is the future penis or clitoris

Question 47

What will the cloacal folds divide into?

Answer 47

Anal and urethral divisions The urogenital septum separates the cloacal (urethral) fold from the anal fold

Question 48

What will appear next to the urethral folds?

Answer 48

Genital swellings These form the future scrotum or labia majora

Question 49

What is development of male external genitalia dependent on?

Answer 49

Androgens - testosterone

Question 50

How does testosterone affect the genital tubercle?

Answer 50

It drives elongation of the genital tubercle to form the phallus As the genital tubercle elongates, it pulls the urethral groove with it

Question 51

What is the urethral groove?

Answer 51

It is the space between the urethral folds

Question 52

What happens to the genital swellings as the genital tubercle develops?

Answer 52

The genital swellings enlarge and move caudally

Question 53

What is the urethral plate?

Answer 53

A thickening of the urethral groove

Question 54

What happens to the urethral folds at the end of the 3rd month?

Answer 54

The urethral folds close over the urethral plate to form the penile urethra

Question 55

What happens to the scrotal swellings at the end of the 3rd month?

Answer 55

They fuse in the midline They are separated by the scrotal septum

Question 56

What causes hypospadias?

Answer 56

Incomplete fusion of the urethral folds The urethra opens on the ventral surface of penis

Question 57

how many births are affected by hypospadias? What does it lead to and how can it be repaired?

Answer 57

3-5 in 1,000 births It causes difficulty urinating It can be repaired surgically using the foreskin

Question 58

What is epispadias?

Answer 58

The urethra opens on the dorsal side of the penis It often is associated with exstrophy of the bladder

Question 59

How many births are affected by epispadias?

Answer 59

1 in 30,000

Question 60

What causes epispadias?

Answer 60

Improper location of the genital tubercle posterior to the urogenital sinus This means the urethral groove is located on the dorsal surface of the penis

Question 61

What is development of the female external genitalia dependent on?

Answer 61

Oestrogens

Question 62

What happens to the genital tubercle in development of female external genitalia?

Answer 62

The genital tubercle elongates slightly to form the clitoris

Question 63

What happens to the urethral folds and genital swellings in development of the female external genitalia?

Answer 63

The urethral folds do NOT fuse and go to form the labia minora Genital swellings form the labia majora

Question 64

What happens to the urogenital groove in female development>

Answer 64

it remains open