12 - Male Embryogenesis

Question 1

What systems develop from the ectoderm

Answer 1

Reproductive tract
Nervous system (hypothalamus and pituitary)
Oral cavity
Nasal cavity

Question 2

What parts of the reproductive tract originate from the ectoderm? Mesoderm?

Answer 2

Ecto
Vagina (external)
Penis or clitoris

Meso
Gonads (ovaries/testes)
Uterus, cervix, internal vagina
Epididymus ductus deferens, accessory sex glands

Question 3

What systems develop from the mesoderm

Answer 3

Repro
Urinary
Skeletal
Blood vessels
Muscle

Question 4

What systems develop from the endoderm

Answer 4

Digestive
Respiratory
Glandular

Question 5

Seven major steps in the embryonic development of the male repro system

Answer 5

1. Development of hypothalamic - hypophyseal system
2. Migration of primordial germ cells from the yolk sac
3. Sex cords develop in gonad and mesonephric renal system transformation
4. Sexual differentiation
5. Development of male ducts, organs and testes
6. Testicular descent into the scrotum
7. Masculinization / defeminization of the hypothalamus

Question 6

Describe the development of the hypophyseal system

Answer 6

Infundibulum hooks around Rathke’s pouch
Infundibulum becomes posterior lobe
Rathkes pouch becomes anterior lobe

Question 7

How is the male hypothalamus different

Answer 7

It is defeminized during embryonic/fetal development and the surge center does not develop

Question 8

What interaction plays an important role in not defeminizing the female hypothalamus?

Answer 8

Estradiol with the carrier protein alph-fetoprotein

Question 9

Slides 9,10

Answer 9

Look, defeminization of the hypothalamus

Question 10

When is hypothalamic defeminization initiated? Complete defeminization requires what?

Answer 10

Initiated when fetal testes start to produce T4 (mid-late period of first trimester)

Complete defeminization requires postnatal exposure to T4

Question 11

What happens to bull calves castrated at or near birth?

Answer 11

Drop of testes takes place later, so it can lead to the bull retaining some surge center function and produce GnRH surges

Question 12

Primordial germ cells migrate from where to where?

Answer 12

Yolk into the gonadal ridge/primitive sex cords

Question 13

Three embryonic renal systems

Answer 13

1. Pronephros
2. Mesonephros
3. Metanephros

Question 14

What is the pronephros

Answer 14

Most primitive form of kidney found in the developing embryo - limited function and eventually degenerates

Question 15

What is the mesonephros

Answer 15

functional kidneys of early mammalian embryo – eventually regresses and gives way to the
Metonephros – remnants of the Mesonephric renal system remain and become portions of the reproductive tracts

Question 16

What part of the mesonephros becomes the female vs male reproductive tract?

Answer 16

Mesonephric ducts (Wolffian) become the male

Paramesonephric ducts (Mullerian) become the female

Question 17

What is the metanephros

Answer 17

final renal system that will eventually become the functioning kidneys in the adult animal

Question 18

Slide 14, 15, 16

Answer 18

Look

Question 19

How does male sex determination work

Answer 19

Gene in Y chromosome produces testes determining factor which triggers testes development
Sertoli cells of the testes secrete anti-mullerian hormone
AMH causes leydig cells to differentiate and produce testosterone and dihydrotestosterone
AMH also degenerates the paramesonephric duct

Question 20

What does testosterone do in sex determination? Dihydrotestosterone?

Answer 20

Test: develops the male duct system

Dihydro: develops the penis, scrotum and accessory sex glands

Question 21

Steroid pathway to estradiol vs dihydrotestosterone

Answer 21

Progesterone -> testosterone – (aromatase enzyme) –> estradiol

Progesterone -> testosterone – (5a reductase enzyme) –> dihydrotestosterone

Question 22

Two anomalies in male sex differentiation

Answer 22

1. Gonadal dysgenesis
2. Male hermaphrodism

Question 23

What is gonadal dysgenesis? E.g.

Answer 23

Incomplete development of testes
e.g. XXY male (klinefelter’s syndrome): extra X chromosome = malformation of seminiferous tubules and low sperm production

Question 24

Two types of male hermaphrodism

Answer 24

• T4 deficiency or insensitivity (receptor mutation): testes present but incomplete ducts
• 5a reductase deficiency: unable to convert T4 to dihydrotestosterone = testes and ducts present but with feminized external genitalia

Question 25

Slide 18, 19

Answer 25

Structure of the testis
Mesonephric development

Question 26

Mesonephric ducts become what in the male

Answer 26

Efferent ducts, epididymus, ductus deferens
Slide 20*

Question 27

Urogenital sinus becomes what in the male

Answer 27

Urethra and male accessory sex glands

Question 28

Four major steps in the descent of the testes

Answer 28

1. Peritoneum in the inguinal regional and testicular gubernaculum join
2. Growth and elongation of the fetal body away from the testes
3. Rapid growth of the gubernaculum in the scrotal region
4. Shrinkage of the gubernaculum within the scrotum

Question 29

Slides 21-26

Answer 29

SUPER IMPORTANT***descent of testes

Question 30

The cavity between the visceral and parental tunics is called the… When does it develop

Answer 30

Vaginal cavity

After the gubernaculum regresses into a small knot attaching the testis to the bottom of the scrotum

Question 31

Two testicular descent abnormalities

Answer 31

1. Cryptorchidism: failure of the testis or testes to descend out of the body cavity into the scrotum
2. Inguinal herniation: portion of the gut (i.e. intestine) passes through the inguinal canal and enters the scrotal vaginal cavity

Question 32

Two types of cryptorchidism and their effects

Answer 32

Bilateral cryptorchidism = infertility

Unilateral cryptorchidism = reduced fertility

Question 33

Slides 28-30

Answer 33

Images of cryptorchidism and inguinal herniation