Prenatal Development

Question 1

When is genetic sex determined?

Answer 1

At the time of fertilization

Question 2

First step in prenatal development

Answer 2

Primordial germ cells from the yolk sac/ allantois migrate into the gonadal ridge in the first trimester

Question 3

What is the gonadal ridge classified as?

Answer 3

Bipotential (decides on sex based on genetic info)

Question 4

How is the embryo a male?

Answer 4

Sperm with Y chromosome with SRY gene

Question 5

What cells are present on the gonadal ridge?

Answer 5

Precursor cells (2)
Primordial germ cells

Question 6

What do the precursor cells in the male become?

Answer 6

Sertoli cells that secrete desert hedgehog and anti-mullarian hormone

Question 7

Desert Hedgehog

Answer 7

Tells the second precursor cells to become Leydig cells that produce Testosterone

Question 8

What do the primordial germ cells in the male become?

Answer 8

Gonacytes that produce sperm throughout the male’s life

Question 9

Mesonephric Duct (wolffian duct) in males

Answer 9

Gives rise to male internal genitalia
Testosterone is essential for development

Question 10

Paramesophric duct (Mullarian duct) in males

Answer 10

Degernerates due to AMH

Question 11

What happens after Leydig cells secrete testosterone?

Answer 11

Development of testis and regression of the mesonephros (temporary version of the kidney)

Question 12

What does the remnant mesonephros give rise to in males?

Answer 12

Future efferent duct after combining with epithelial cords (future seminiferous tubules)

Question 13

What does the mesonephric duct generate in males?

Answer 13

Epididymus and vas deferens

Question 14

Dihydrotesterone

Answer 14

5a-reductase will convert testosterone into dihydrotesterone to develop into external genitalia because it’s 100 times more potent than testosterone

Question 15

What does the genital tubercle become in males?

Answer 15

Glans penis

Question 16

What does the urogenital/ genital folds become in males?

Answer 16

Fuse to form the ventral aspect of the penis

Question 17

What does the labioscrotal/genital swelling do in males?

Answer 17

Become the scrotum

Question 18

How is the female embryo developed?

Answer 18

Egg is fertilized with sperm with the XX genotype (SRY gene absent)- default pathway

Question 19

For the female, what does the primordial germ cells give rise to?

Answer 19

The eggs

Question 20

For the female, what do precursor cells become?

Answer 20

Granulosa (follicle cells) that secrete theca cells that secrete estrogen

Question 21

Which structures regress in the female?

Answer 21

Mesonephros tubules and epithelial cords
Mesonephric duct as well because no testosterone

Question 22

What does the Coelomic epithelium become?

Answer 22

Future cortex

Question 23

What does the Paramesonephric duct become in females?

Answer 23

Develop into internal female genitalia (uterus, cervix, part of the vagina, oviduct) due to the absence of the AMH

Question 24

For the female what does the Cranial and caudal urogentical sinuses develop into?

Answer 24

Bladder and vestibule respectively

Question 25

In females, what does the genital tubercle become?

Answer 25

Clitoris

Question 26

In females what does the urogentical fold do?

Answer 26

Remain separate as the labia minora

Question 27

In females, what does the labioscrotal swelling become?

Answer 27

The labia majora where the remain fused

Question 28

Karyotype XY-SRY Mutation

Answer 28

No desert hedgehog, leydig cells, T, DHT–> mesonephric duct generateates and male system doesn’t develop –> external genitalia of the female
No Sertoli cells, AMH –>Mullerian ducts develop producing female genitalia

Question 29

What happens to animals with the XY-SRY mutation?

Answer 29

Dysfunctional ovary with female internal and external genitalia
Common in horses

Question 30

Persistent Mullerian Duct Syndrome

Answer 30

Sertoli cells form but don’t secrete AMH (mutation in the AMH gene)
The individual will have internal female and male genitalia and external male genitalia

Question 31

Complete Androgen Insensitivity Syndrome

Answer 31

Mutation in the androgen receptor so T and DHT can’t activate downstream signaling

Question 32

What is the outcome of androgen insensitivity syndrome?

Answer 32

Abnormal development of the male duct system
Female external genitalia will develop

Question 33

Freemartin statistics in cattle

Answer 33

92% of heterosexual twins result in freemartin heifer
86,000 freemartin calves born annually in the US

Question 34

Twins in cattle

Answer 34

Common blood supply between two fetuses due to fusion of chorio-allantois portion of the placenta
5% twinning rate i Holstein cattle

Question 35

What happens to the females during freemartin?

Answer 35

Due to shared blood supply with male, female fetus is exposed to AMH and testosterone
Wide variation in external genitalia, maldevelopment or no development of internal genitalia

Question 36

Transabdominal Phase of Testicular Descent

Answer 36

Enlargement of the distal gubernaculum, making it short and fat (swelling)
Regulated by insulin-like 3 (ligand) protein secreted by leydig cells and pancreas

Question 37

Inguinal-Scrotal phase of Testicular Descent

Answer 37

Testis moves through inguinal region because gubernaculum shrinks
Shrinks and pull testis deeper into the scrotum
Controlled by T (androgen receptor)

Question 38

What are the testicular descent abnormalities?

Answer 38

Cryptorchidism
Inguinal Hernia