Midterm 2 - Lecture 14 Flashcards
Embryonic origin of organs/systems from the ectoderm
- reproductive tract
- penis - nervous system
- hypothalamus
- anterior and posterior pituitary - oral cavity
- nasal cavity
Embryonic origin of organs and systems from the mesoderm
- reproductive system
- gonads (testes)
- epididymus, ductus deferens, accessory sex glands - urinary system
- skeletal system
- blood vessels
- muscle
Embryonic origin of organs and systems from the endoderm
- digestive system
- respiratory system
- glandular systems
Embryonic development of the reproductive system
- Development of hypothalamic-hypophyseal system
- migration of primordial germ cells from the yolk sac
- sex cords develop in gonad and mesonephric renal system regresses
- sexual differentiation - sex evident from structures
- development of male ducts, organs and testes
- testicular descent into the scrotum
- masculinization/defeminization of hypothalamus
Where is the posterior lobe of the pituitary derived from?
infundibulum
Where is the anterior lobe of the pituitary derived from?
Rathke’s pouch
Does the male hypothalamus contain a surge center?
NO! only a tonic center
What does it mean by the male hypothalamus is “defeminized” during embryonic development?
- surge center does not develop
What interaction plays an important role in not defeminizing the female hypothalamus?
- interaction of Estradiol with the “carrier-protein” alpha-fetoprotein
How is the hypothalamus defeminized in males?
- 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
Timeline of male hypothalamus defeminization
- 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
What does the reproductive system develop in close proximity and at the same time as?
- the renal system
What are the three embryonic renal systems?
- pronephros
- mesonephros
- metanephros
Pronephros
- most primitive for of kidney found in the developing embryo
- limited fxn and eventually degenerates
Mesonephros
- 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
Metanephros
- final renal system that will eventually become the fxning kidneys in the adult animal
Sex determining factors
- Testis determining factor (TDF)
- Testes develop
- Sertoli cells secrete anti-mullerian hormone (AMH)
- AMH causes degeneration of paramesonephric duct AND leydig cells to differentiate
- Testosterone ——-> development of male duct system
- Dihydrotestosterone ————-> development of penis, scrotum, and accessory sex glands
Steroid pathway starting at progesterone
- progesterone to T4
a. 5alpha-reductase produces dihydrotesterone
b. aromatase produces E2
2 abnormalities of sexual differentiation
- gonadal dysgenesis
- male hermaphrodism
Gonadal dysgenesis
- incomplete development of testes
- Ex. XXY Male (Klinefelter’s Syndrome) = malformation of seminiferous tubules; extremely low sperm production
Male hermaphrodism
- 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
Fate of ambisexual undifferentiated gonad
testis
Fate of ambisexual paramesonephros ducts (mullerian ducts)
regresses
Fate of ambisexual mesonephros ducts (Wolffian ducts)
- efferent ducts
- epididymus
- ductus deferens
Fate of ambisexual urogenital sinus
- urethra
- accessory sex glands
4 major steps of the descent of the testes
- peritoneum in the inguinal regional and testicular gubernaculum join (testicular anchor)
- growth and elongation of the fetal body away from the testes
- as the body elongates the testes remain stationary in the lower abdomen - 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 - 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
2 abnormalities of testicular descent
- cryptorchidism
- inguinal herniation
Cryptorchidism
- 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
Inguinal Herniation
- portion of the gut (intestine) passes through the inguinal canal and enters the scrotal vaginal cavity
