Midterm 2 - Lecture 14

Question 1

Embryonic origin of organs/systems from the ectoderm

Answer 1

1. reproductive tract
   - penis
2. nervous system
   - hypothalamus
   - anterior and posterior pituitary
3. oral cavity
4. nasal cavity

Question 2

Embryonic origin of organs and systems from the mesoderm

Answer 2

1. reproductive system
   - gonads (testes)
   - epididymus, ductus deferens, accessory sex glands
2. urinary system
3. skeletal system
4. blood vessels
5. muscle

Question 3

Embryonic origin of organs and systems from the endoderm

Answer 3

1. digestive system
2. respiratory system
3. glandular systems

Question 4

Embryonic development of the reproductive system

Answer 4

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 regresses
4. sexual differentiation - sex evident from structures
5. development of male ducts, organs and testes
6. testicular descent into the scrotum
7. masculinization/defeminization of hypothalamus

Question 5

Where is the posterior lobe of the pituitary derived from?

Answer 5

infundibulum

Question 6

Where is the anterior lobe of the pituitary derived from?

Answer 6

Rathke’s pouch

Question 7

Does the male hypothalamus contain a surge center?

Answer 7

NO! only a tonic center

Question 8

What does it mean by the male hypothalamus is “defeminized” during embryonic development?

Answer 8

• surge center does not develop

Question 9

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

Answer 9

• interaction of Estradiol with the “carrier-protein” alpha-fetoprotein

Question 10

How is the hypothalamus defeminized in males?

Answer 10

• fetal testis produces Testosterone
• T4 interacts with alpha-fetoprotein and is able to cross the blood brain barrier
• aromatase then converts T4 into E2 and the surge center does not develop
  *it is actually the estradiol that defeminizes the surge center; but only T4 can cross the barrier

Question 11

Timeline of male hypothalamus defeminization

Answer 11

• process initiated when fetal testes starts to produce T4 (mid-late period of the 1st trimester)
• complete defeminization requires postnatal exposure to T4
  *bull calves castrated at or near birth retain some surge center fxn and produce GnRH surges

Question 12

What does the reproductive system develop in close proximity and at the same time as?

Answer 12

• the renal system

Question 13

What are the three embryonic renal systems?

Answer 13

1. pronephros
2. mesonephros
3. metanephros

Question 14

Pronephros

Answer 14

• most primitive for of kidney found in the developing embryo
• limited fxn and eventually degenerates

Question 15

Mesonephros

Answer 15

• fxnl kidneys of early mammalian embryo
• eventually regresses and gives way to the metanephros
• remnants of the mesonephros system remain and become portions of the repro tract
• Mesonephric ducts (Wolffian ducts) contribute to male tract; paramesonephric ducts regress

Question 16

Metanephros

Answer 16

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

Question 17

Sex determining factors

Answer 17

1. Testis determining factor (TDF)
2. Testes develop
3. Sertoli cells secrete anti-mullerian hormone (AMH)
4. AMH causes degeneration of paramesonephric duct AND leydig cells to differentiate
5. Testosterone ——-> development of male duct system
6. Dihydrotestosterone ————-> development of penis, scrotum, and accessory sex glands

Question 18

Steroid pathway starting at progesterone

Answer 18

• progesterone to T4
  a. 5alpha-reductase produces dihydrotesterone
  b. aromatase produces E2

Question 19

2 abnormalities of sexual differentiation

Answer 19

1. gonadal dysgenesis
2. male hermaphrodism

Question 20

Gonadal dysgenesis

Answer 20

• incomplete development of testes
• Ex. XXY Male (Klinefelter’s Syndrome) = malformation of seminiferous tubules; extremely low sperm production

Question 21

Male hermaphrodism

Answer 21

• T4 deficiency or T4 insensitivity = testes present but incomplete ducts and/or external genitalia
• 5alpha reductase deficiency = unable to convert T4 to dihydrotestosterone; tests and ducts present but with feminized external genitalia

Question 22

Fate of ambisexual undifferentiated gonad

Answer 22

testis

Question 23

Fate of ambisexual paramesonephros ducts (mullerian ducts)

Answer 23

regresses

Question 24

Fate of ambisexual mesonephros ducts (Wolffian ducts)

Answer 24

• efferent ducts
• epididymus
• ductus deferens

Question 25

Fate of ambisexual urogenital sinus

Answer 25

• urethra
• accessory sex glands

Question 26

4 major steps of the descent of the testes

Answer 26

1. peritoneum in the inguinal regional and testicular gubernaculum join (testicular anchor)
2. growth and elongation of the fetal body away from the testes
   - as the body elongates the testes remain stationary in the lower abdomen
3. rapid growth of the gubernaculum in the scrotal region
   - as gubernaculum expands laterally it shortens and pulls testis through the inguinal canal
   - gubernaculum expansion creates the scrotal cavity
4. shrinkage of the gubernaculum within the scrotum
   - gubernaculum regresses to a small knot attaching the testis to the bottom of the scrotum
   - the cavity btw the visceral and parental tunics forms creating the scrotal vaginal cavity

Question 27

2 abnormalities of testicular descent

Answer 27

1. cryptorchidism
2. inguinal herniation

Question 28

Cryptorchidism

Answer 28

• failure of the testis or testes to descend out of the body cavity into the scrotum
• bilateral cryptorchidism = infertility
• unilateral cryptorchidism = reduced fertility
• still displays normal male behaviour; T4 production not impacted

Question 29

Inguinal Herniation

Answer 29

• portion of the gut (intestine) passes through the inguinal canal and enters the scrotal vaginal cavity