12 - Male Embryogenesis Flashcards
What systems develop from the ectoderm
Reproductive tract
Nervous system (hypothalamus and pituitary)
Oral cavity
Nasal cavity
What parts of the reproductive tract originate from the ectoderm? Mesoderm?
Ecto
Vagina (external)
Penis or clitoris
Meso
Gonads (ovaries/testes)
Uterus, cervix, internal vagina
Epididymus ductus deferens, accessory sex glands
What systems develop from the mesoderm
Repro
Urinary
Skeletal
Blood vessels
Muscle
What systems develop from the endoderm
Digestive
Respiratory
Glandular
Seven major steps in the embryonic development of the male repro system
- Development of hypothalamic - hypophyseal system
- Migration of primordial germ cells from the yolk sac
- Sex cords develop in gonad and mesonephric renal system transformation
- Sexual differentiation
- Development of male ducts, organs and testes
- Testicular descent into the scrotum
- Masculinization / defeminization of the hypothalamus
Describe the development of the hypophyseal system
Infundibulum hooks around Rathke’s pouch
Infundibulum becomes posterior lobe
Rathkes pouch becomes anterior lobe
How is the male hypothalamus different
It is defeminized during embryonic/fetal development and the surge center does not develop
What interaction plays an important role in not defeminizing the female hypothalamus?
Estradiol with the carrier protein alph-fetoprotein
Slides 9,10
Look, defeminization of the hypothalamus
When is hypothalamic defeminization initiated? Complete defeminization requires what?
Initiated when fetal testes start to produce T4 (mid-late period of first trimester)
Complete defeminization requires postnatal exposure to T4
What happens to bull calves castrated at or near birth?
Drop of testes takes place later, so it can lead to the bull retaining some surge center function and produce GnRH surges
Primordial germ cells migrate from where to where?
Yolk into the gonadal ridge/primitive sex cords
Three embryonic renal systems
- Pronephros
- Mesonephros
- Metanephros
What is the pronephros
Most primitive form of kidney found in the developing embryo - limited function and eventually degenerates
What is the mesonephros
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
What part of the mesonephros becomes the female vs male reproductive tract?
Mesonephric ducts (Wolffian) become the male
Paramesonephric ducts (Mullerian) become the female
What is the metanephros
final renal system that will eventually become the functioning kidneys in the adult animal
Slide 14, 15, 16
Look
How does male sex determination work
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
What does testosterone do in sex determination? Dihydrotestosterone?
Test: develops the male duct system
Dihydro: develops the penis, scrotum and accessory sex glands
Steroid pathway to estradiol vs dihydrotestosterone
Progesterone -> testosterone – (aromatase enzyme) –> estradiol
Progesterone -> testosterone – (5a reductase enzyme) –> dihydrotestosterone
Two anomalies in male sex differentiation
- Gonadal dysgenesis
- Male hermaphrodism
What is gonadal dysgenesis? E.g.
Incomplete development of testes
e.g. XXY male (klinefelter’s syndrome): extra X chromosome = malformation of seminiferous tubules and low sperm production
Two types of male hermaphrodism
- 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
Slide 18, 19
Structure of the testis
Mesonephric development
Mesonephric ducts become what in the male
Efferent ducts, epididymus, ductus deferens
Slide 20*
Urogenital sinus becomes what in the male
Urethra and male accessory sex glands
Four major steps in the descent of the testes
- Peritoneum in the inguinal regional and testicular gubernaculum join
- Growth and elongation of the fetal body away from the testes
- Rapid growth of the gubernaculum in the scrotal region
- Shrinkage of the gubernaculum within the scrotum
Slides 21-26
SUPER IMPORTANT***descent of testes
The cavity between the visceral and parental tunics is called the… When does it develop
Vaginal cavity
After the gubernaculum regresses into a small knot attaching the testis to the bottom of the scrotum
Two testicular descent abnormalities
- Cryptorchidism: failure of the testis or testes to descend out of the body cavity into the scrotum
- Inguinal herniation: portion of the gut (i.e. intestine) passes through the inguinal canal and enters the scrotal vaginal cavity
Two types of cryptorchidism and their effects
Bilateral cryptorchidism = infertility
Unilateral cryptorchidism = reduced fertility
Slides 28-30
Images of cryptorchidism and inguinal herniation
