Embryology-Male Sexual Differentiation Flashcards
What are the different factors that contribute to one’ sex?
Chromosomal sex, gonadal sex, phenotypic sex
When does sexual differentiation begin in utero?
6-7 weeks
What is the consequence of differentiation of the hypothalamus?
The male hypothalamus is no longer able to produce the LH surge necessary for ovulation in females.
What area of the brain has remarkable changes in response to steroids in puberty?
Hypothalamus. The set point for steroid hormone feedback becomes markedly elevated.
Where do the gonads come from?
4-5 wks: genital ridge forms -> Germ cells migrate from yolk sac to genital ridge -> genital ridge seeded w/germ cells
What determines how many eggs a woman will have for the duration of her life?
The number of germ cells that populate the ovaries during gestation.
What ductal systems are associated with the seeding of the gonadal ridge?
Wolffian (mesonephric) duct and Mullerian (paramesonephric) duct. These will develop into the internal sex structures (Wolffian for males and Mullerian for females)
What triggers the differentiation of the gonad into testis?
Y chromosome codes for testis-specific proteins and hormones (testosterone & Mullerian inhibiting hormone) that will transform the gonad into a primitive testis. This all happens around 6-7 weeks.
Which sex is the differentiation by default?
Female: males need testosterone and Mullerian inhibiting hormone to develop male characteristics.
What is the function of Mullerian duct inhibiting factor made by sertoli cells?
Mullerian duct regression, eliminates structures that would become the uterus and fallopian tubes
Drivers for male sexual differentiation
Mullerian inhibiting factor and testosterone
What tells the Leydig cells to make testosterone?
Not the mother’s or the fetal’s hypothalamus, hCG from the placenta is the fetal “LH”.
What structures are dependent on testosterone for development
Wolffian duct (epididymus, vas deferens, seminal vesicles and ejaculatory duct). The urogenital primordia (penis, corpus spongiosum, scrotum, prostate and bulbourethral gland) are all dependent on testosterone conversion to DHT by 5-alpha-reductase.
Why is 5-alpha-reductase essential for almost all tissues in males?
All tissues aside from the Wolffian duct will only react to DHT. Without 5-alpha-reductase testosterone is inactive.
Where do men get their estrogen?
Testis
Does a person with complete testicular feminization have testicles or ovaries? What is their level of testosterone in the blood?
Testis. Testosterone is high, they are feminized because they are deficient in 5-alpha-reductase. In the absence of testosterone the wolffian ducts regress, urogenital folds develop into a clitoris, labia and lower vagina. Since there is still mullerian inhibition substance the oviduct, uterus and upper vagina do not develop.
What contributes to the spectrum of differentiation of male to female in testicular feminization?
Inactive mullerian inhibiting substance allows for differentiation of mullerian ducts (oviduct, uterus and upper vagina). Ranges in 5-alpha-reductase is also a big player.
Ambigous female genitalia due to adrenal problems?
Congenital adrenal hyperplasia -> 21-hyrdoxylase deficiency pushes all steroid hormone precursors towards androgen biosynthesis.
Why don’t girls develop breasts earlier in life?
They hypothalamic set point (cycling center) is very sensitive to feedback inhibition by estrogen and progesterone. At puberty the hypothalamic set point shifts way up and it takes way more estrogen and progesterone to inhibit the hypothalamus. Consequently levels of GnRH go way up and LH/FSH secretion increases. The ovary begins to produce lots of estrogen and progesterone. Males are similar, but with testosterone instead of estrogen and progesterone.
