Development of the Genital Ducts and External Genitalia Flashcards Preview

BS - Reproductive System > Development of the Genital Ducts and External Genitalia > Flashcards

Flashcards in Development of the Genital Ducts and External Genitalia Deck (64)
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1
Q

What is significant about the first 13 weeks in development?

A

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

2
Q

What is the reproductive system derived from?

A

Intermediate mesoderm

This forms the urogenital ridge

3
Q

What develops from the urogenital ridge?

A
  1. urinary system

2. reproductive system

4
Q

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

A

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

The primitive sex cords migrate into the underlying mesenchyme

5
Q

What is the alternative name for primitive sex cords?

A

Medullary cords

6
Q

What is significant about primordial germ cells?

A

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

7
Q

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

A

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

8
Q

What will the Sertoli cells go on to form?

A

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

These are solid cords

9
Q

What do the testes cords go on to form?

A

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

10
Q

What happens to the seminiferous tubules at puberty?

A

They are solid until puberty

At puberty they recanalise, allowing the male to produce sperm

11
Q

How does TDF influence the male gonadal development?

A

TDF maintains the medullary cords

12
Q

How do the primordial germ cells influence female gonadal development?

A

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

Cortical cords develop

13
Q

What do the cortical cords go on to form?

A

The somatic support cells in the cortical cords invest the PGCs

This leads to formation of primordial follicles

14
Q

What duct system remains in male development?

A

TDF maintains the mesonephric ducts

The paramesonephric duct is broken down

15
Q

What duct system remains in female development?

A

Absence of TDF causes the mesonephric duct to break down

The paramesonephric duct continues to develop

16
Q

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

A

The paramesonephric duct system is the Müllerian system

The mesonephric duct system is the Wolffian system

17
Q

What encodes TDF and drives development of male genital ducts?

A

The SRY gene encodes for TDF

This is testis determining factor (TDF)

18
Q

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

A

Sertoli cells secrete anti-müllerian hormone (AMH)

19
Q

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

A

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

20
Q

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

A

They cause differentiation of the mesenchyme into Leydig cells

21
Q

What is the role of Leydig cells?

A

They produce testosterone

This promotes maintenance and further development of mesonephric ducts

22
Q

What 4 structures will the mesonephric duct develop into?

A
  1. efferent ductules
  2. epididymis
  3. vas deferens
  4. seminal vesicle
23
Q

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

A
  1. appendix testis

2. utriculus prostaticus

24
Q

Why do the paramesonephric ducts develop in females?

A

There is no anti-müllerian hormone

The paramesonephric ducts remain

25
Q

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

A

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

26
Q

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

A

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

27
Q

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

A
  1. cranial
  2. horizontal
  3. caudal

Cranial and horizontal parts become the uterine tubes

Caudal parts fuse to form the uterine canal

28
Q

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

A
  1. Epoophoron
  2. Paraoophoron
  3. Gartner’s cyst
29
Q

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

A

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

30
Q

How does the cloaca divide?

What are the 2 parts formed?

A

The urorectal septum continues to develop to separate the cranial and caudal parts of the cloaca

Cranial part - urogenital sinus

Caudal part - anorectal canal

31
Q

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

A

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

32
Q

How does the vagina form?

A

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

33
Q

What are the 2 origins of the vagina?

A
  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)
34
Q

What can cause double uterus and double vagina?

A

Failure of caudal tips of paramesonephric ducts to fuse together

35
Q

What causes double uterus?

but only one vagina

A

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

36
Q

What causes bicornate uterus?

A

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

37
Q

What causes cervical atresia?

What is this?

A

The caudal tips of the paramesonephric ducts only just meet

This leads to the cervix being very thin

38
Q

What causes unicornate uterus?

A

Only one paramesonephric duct doesn’t develop properly

This leads to only one uterine tube being present

39
Q

What is septated uterus and what causes it?

A

The septum between the 2 paramesonephric ducts may break down

40
Q

What % of fertile women are affected by abnormalities of the uterus?

What are the risks associated with this?

A

1%

This leads to higher rates of:

  1. miscarriage
  2. premature delivery
  3. dystocia (difficult birth)
41
Q

What causes persistent müllerian duct syndrome?

A

A mutation in the AMH gene

This means there is no anti-müllerian hormone so the paramesonephric ducts persist

42
Q

What is involved in persistent müllerian duct syndrome?

A

Both mesonephric and paramesonephric duct derivatives develop

There are developing testes, but a uterus also develops

43
Q

What are the genitalia like in persistent müllerian duct syndrome?

A

There is normal male genitalia but it is associated with cryptorchidism

44
Q

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

A

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

45
Q

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

A

Mesoderm cells migrate to surround the cloacal membrane

They form elevations called cloacal folds

46
Q

What do the cloacal folds go on to form?

A

Cloacal folds unite anteriorly to form the genital tubercle

This is the future penis or clitoris

47
Q

What will the cloacal folds divide into?

A

Anal and urethral divisions

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

48
Q

What will appear next to the urethral folds?

A

Genital swellings

These form the future scrotum or labia majora

49
Q

What is development of male external genitalia dependent on?

A

Androgens - testosterone

50
Q

How does testosterone affect the genital tubercle?

A

It drives elongation of the genital tubercle to form the phallus

As the genital tubercle elongates, it pulls the urethral groove with it

51
Q

What is the urethral groove?

A

It is the space between the urethral folds

52
Q

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

A

The genital swellings enlarge and move caudally

53
Q

What is the urethral plate?

A

A thickening of the urethral groove

54
Q

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

A

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

55
Q

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

A

They fuse in the midline

They are separated by the scrotal septum

56
Q

What causes hypospadias?

A

Incomplete fusion of the urethral folds

The urethra opens on the ventral surface of penis

57
Q

how many births are affected by hypospadias?

What does it lead to and how can it be repaired?

A

3-5 in 1,000 births

It causes difficulty urinating

It can be repaired surgically using the foreskin

58
Q

What is epispadias?

A

The urethra opens on the dorsal side of the penis

It often is associated with exstrophy of the bladder

59
Q

How many births are affected by epispadias?

A

1 in 30,000

60
Q

What causes epispadias?

A

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

61
Q

What is development of the female external genitalia dependent on?

A

Oestrogens

62
Q

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

A

The genital tubercle elongates slightly to form the clitoris

63
Q

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

A

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

Genital swellings form the labia majora

64
Q

What happens to the urogenital groove in female development>

A

it remains open