Embryology - External Genitalia

Question 1

Where is the reproductive system derived from?

Answer 1

Intermediate mesoderm

Question 2

What is the urogenital ridge?

Answer 2

Thickening of epithelium that starts to produce primitive sex cords

Question 3

Where do the primordial germ cells come from?

Answer 3

Yolk sac (see embryology 1)

Question 4

What do the primordial germ cells contain?

Answer 4

Autosomes (XX or XY chromosomes)

Question 5

Briefly describe order of male gonadal development

Answer 5

1. Medullary cords develop
2. Sertoli cells
3. Testes cords
4. Seminiferous tubules

Question 6

When are seminiferous tubules solid up until?

Answer 6

Puberty

Tubes hollow and allow male to produce sperm

Question 7

Briefly describe order of female gonadal development

Answer 7

1. Medullary cords break down and cortical cords develop
2. Follicle cells
3. Primordial follicles

Question 8

Why do females already contain eggs ready for development at birth?

Answer 8

Cortical cords invest primordial germ cells

Form follicle germ cells which stimulates germ cells to change –> undergo 1st stage of meiosis

Question 9

In the first weeks of development, what two pairs of ducts do all embryos contain?

Where do both of these ducts end?

Answer 9

1. Mesonephric duct
2. Paramesonephric duct

Both end at the cloaca

Question 10

Which duct develops in males?

Answer 10

Presence of TDF and testosterone (produced by Leidig cells) causes the mesonephric ducts to develop

Question 11

What do the mesonephric ducts develop to form in males?

Answer 11

The primary male genital ducts

Question 12

What happens to the paramesonephric ducts in males? What causes this?

Answer 12

They regress due to presence of anti-Mullerian hormone

Question 13

What is anti-Mullerian hormone produced by?

Answer 13

Sertoli cells in the testes

Question 14

Which ducts degenerate in females? Why?

Answer 14

The mesonephric ducts degenerate due to absence of testosterone

Question 15

Which ducts develop in females?

Answer 15

Paramesonephric ducts develop due to absence of anti-mullerian hormone

Question 16

What remnant of the mesonephric ducts are left behind in females?

Answer 16

Gartner’s duct (a vestigial remnant)

Question 17

What are mesonephric ducts sometimes called?

Answer 17

Wolffian ducts

Question 18

What are paramesonephric ducts sometimes called?

Answer 18

Mullerian ducts

Question 19

What does the SRY gene encode for?

Answer 19

Testis Determining Factor (TDF)

Question 20

When the somatic support cells invest the primordial germ cells with the SRY gene, what forms?

Answer 20

Differentiate into Sertoli cells

Question 21

What hormone does Sertoli cells secrete?

Answer 21

Anti-mullerian hormone (AMH)

Question 22

What does AMH cause?

Answer 22

Degeneration of paramesonephric ducts

Question 23

Sertoli cells cause the differentiation of the mesoderm of the gonad into what?

Answer 23

Leydig cells

Question 24

Where are the Leydig cells located?

Answer 24

In between testis cords

Question 25

What do Leydig cells produce?

Answer 25

Testosterone

Question 26

What is job of testosterone in development?

Answer 26

Promotes maintenance and further development of mesonephric ducts

Question 27

What does the mesonephric duct in males develop into?

Answer 27

- Efferent ductules - Epididymis - Vas deferens - Seminal vesicle

Question 28

What are the remnants of the paramesonephric duct in males?

Answer 28

- Appendix testis | - Utriculus prostaticus

Question 29

Describe the appendix testis

Answer 29

A small portion of tissue located on the upper pole of each testicle, which has no physiological function.

Question 30

Where does the reproductive system empty into urinary system in males?

Answer 30

Prostatic urethra

Question 31

Describe journey of sperm to prostatic urethra

Answer 31

1. Sperm made in testis cords/seminiferous tubules 2. Sperm passed to rete testis 3. Passes to efferent ductules 4. Passes to epididymis 5. Vas deferens carries to prostatic urethra (meets wth seminal vesicles before)

Question 32

What happens to the caudal tips of the 2 paramesonephric ducts in females?

Answer 32

They fuse together to form the uterus, cervix and upper 1/3 of vagina

Question 33

What does the cranial part of the paramesonephric duct form?

Answer 33

Uterine tubes

Question 34

Initially, what 3 are the paramesonephric ducts described as having?

Answer 34

1. Cranial 2. Horizontal 3. Caudal

Question 35

What does the horizontal part of the paramesonephric ducts form?

Answer 35

Uterine tubes

Question 36

What remnants of the mesonephric ducts persist in females?

Answer 36

1. Epophoron 2. Paraoophoron 3. Gartners cyst

Question 37

What does the cloaca divide into? What is it separated by?

Answer 37

1. Urogenital sinus 2. Anus Separated by urorectal sinus

Question 38

What forms the lower 2/3 of the vagina?

Answer 38

Sinovaginal bulbs

Question 39

Where do the sinovaginal bulbs develop from? How do they form the vagina?

Answer 39

Sinovaginal bulbs develop from urogenital sinus that fuse with caudal tips of paramesonephric ducts to form vagina

Question 40

What type of structure does: 1. Distal 2/3 of vagina 2. Uterus, cervix, upper 1/3 of vagina develop from?

Answer 40

Distal 2/3 of vagina: endoderm (from sinovaginal bulbs) Uterus, cervix, upper 1/3 of vagina: intermediate mesoderm (from paramesonephric ducts)

Question 41

What is the hymen?

Answer 41

Membrane between sinovaginal bulbs developing cranially and paramesonephric ducts developing caudally

Question 42

What can cause abnormalities of uterus?

Answer 42

1. Failure of paramesonephric ducts to fuse 2. Failure of uterine septum to degenerate 3. Failure of one paramesonephric duct to elongate

Question 43

What can failure of paramesonephric ducts to fuse cause?

Answer 43

Double uterus, double vagina

Question 44

What is bicornate uterus?

Answer 44

Incomplete fusion of paramesonephric ducts so there are 2 distinct uterine horns entering into single vagina

Question 45

What are dangers of uterus abnormalities?

Answer 45

Higher rates of miscarriage, premature delivery, dystocia (difficult birth)

Question 46

What is persisten mullerian duct syndrome?

Answer 46

Genetic male Mutation in AMH gene so no AMH production Paramesonephric ducts persist Both mesonephric duct and paramesonephric duct derivatives develop (uterine tubes and primitive uterus too) Normal male external genitalia but associated with cryptorchidism

Question 47

What is cryptorchidism?

Answer 47

One or both of the testes fail to descend from the abdomen into the scrotum.

Question 48

When does the development of the external genitalia begin?

Answer 48

In 3rd week of development

Question 49

What happens in the 'indifferent stage' in development of external genitalia?

Answer 49

Either side of urogenital sinus, mesoderm/mesenchymal cells from primitive streak migrate to surround cloacal membrane to form cloacal folds (elevations)

Question 50

What then happens to these cloacal folds (cranially)?

Answer 50

Fuse together cranially to form genital tubercle

Question 51

What will the genital tubercle go on to form?

Answer 51

Future penis or clitoris

Question 52

What do these cloacal folds divide into caudally?

Answer 52

Anal folds (posteriorly) and urethral folds (anteriorly)

Question 53

What appears next to the urethral folds?

Answer 53

Genital swellings

Question 54

What will the genital swellings go on to form?

Answer 54

Future scrotum or labia majora

Question 55

What is the development of male external genitalia driven by?

Answer 55

Androgens, namely dihydrotestosterone (DHT).

Question 56

Describe the development of the genital tubercle in males?

Answer 56

Elongates to form phallus

Question 57

What is found between the urethral folds in males?

Answer 57

Urethral folds pulled together to form urethral groove (urethral folds form lateral walls of urethral groove)

Question 58

What is the urethral groove lined by?

Answer 58

Lined by epithelium and form urethral plate (thickening)

Question 59

Which side of the penis is ventral/dorsal when it is flaccid?

Answer 59

The bit you see is the dorsal (back) surface. Need to lift us penis to see ventral (front ) surface.

Question 60

What is the penis like in the anatomical position?

Answer 60

Erect

Question 61

What does the urethral groove go on to form?

Answer 61

Genital tubercle elongates and pulls urethral groove with it. This extends along the caudal aspect of the phallus. The folds close over at end of 3rd month, forming the penile urethra.

Question 62

What do the genital swellings in males become?

Answer 62

Scrotal swellings

Question 63

How do scrotal swellings migrate? What then happens?

Answer 63

Migrate caudally and fuse in midline to form scrotum (separated by scrotal septum)

Question 64

What is hypospadias? What is it caused by?

Answer 64

Urethra opening on underside (ventral side) of penis instead of at tip

Question 65

What are complications of hypospadias? How can it be repaired?

Answer 65

- Difficulty urinating | - Can be repaired surgically using foreskin

Question 66

What is epispadias? What is it caused by?

Answer 66

Urethra opening on dorsal surface of penis (upper aspect) Caused by improper location of genital tubercle posterior to urogenital sinus --> urethral groove located on dorsal surface of penis

Question 67

What is epispadias often associated with?

Answer 67

Bladder exstrophy

Question 68

What is bladder exstrophy?

Answer 68

A congenital abnormality that occurs when the skin over the lower abdominal wall does not form properly. The bladder is open and exposed on the outside of the abdomen.

Question 69

What is development of female external genitalia driven by?

Answer 69

Oestrogens

Question 70

How does genital tubercle develop in females?

Answer 70

Elongates slightly to form clitoris

Question 71

Describe development of urethral folds in females?

Answer 71

Urethral folds don't fuse --> form labia majora Urogenital groove remains open