Repro development and differentiation Flashcards
Sexual differentiation starts where?
At the genetic level with the presence or absence of Y
What is on the Y chromosome that stimulates male development?
Testis-determining factor
What gene encodes the TDF?
SRY gene
What cells are involved in gonadal differntiation?
Primordial germ cells from the hindgut mesentery migrate to the gonadal ridge at about 5 wks gestation
What happens when PGC migrate?
They stimulate development of indifferent gonads with a cortex and medulla
What is the first steps in female gonadal differentiation?
The medulla regresses and PGC migrate to the cortex, multiply and differntiate into oogonia
What are the first steps in male gonadal differentiation?
SRY gene induces expression of SOX9 and Fgf9 which stimulate the development primitive sex chords in the medulla of the indifferent gonad which becomes the seminiferous tubules and rete testes and the cortex regresses. PCG develop into spermatogonia and medullary cells become sertoli cells. Cells from the cortex become leydig cells
What are the two duct systems in male and female?
- Mesonephric duct
- Paramesonephric
What duct system is found in females?
The mesonephric degenerate and the paramesonephric develops into fimbriae, uterine tubes, uterus, cervix, and upper vagina
What duct system is in males?
Paramesonephric ducts regress due to AMH binding to AMHRII in the duct. Testosterone binds to AR in mesonephric ducts and stimulates the epididymis, vas deferens, seminal vesicle, and ejaculatory duct
How do AMH and testosterone act?
Ipsilaterally in development
What does genitalia consist of in the indifferent stage?
- Genital fold
- genital swelling
- Genital tubercle
What spurs development of male external genitalia?
Dihydrotestosterone from the testosterone
What spurs development of female external development?
Estrogen from the ovaries
Is the surge center formed in males or females?
Females
Why do males not have a surge center?
Androgen from the fetal testis cross the blood brain barrier and are converted to estradiol in the hypothalamus which suppresses the formation
SRY expression results in what hormones?
Androgens (testosterone and DHT) and Antimullerian hormone (AMH)
Lack of AMH and androgens does what?
Stimulate development of female internal genitalia
What stimulates development of female external genitalia and brain?
Estrogens
What does AMH/androgens stimulate?
Development of male internal and external genitalia and brain
Lack of SRY expression causes what?
Differentiation of gonads to ovaries that secrete estrogens
Where does control of repro function start?
Hypothalamus
Why do females develop a surge center when there is estradiol release from the ovaries?
They produce alpha fetoprotein that prevents it from crossing the blood brain barrier
What hormones acts on gonadotrophs to secrete LH and FSH?
GnRH
Estrogens have what feedback on the hypothalamic surge center?
Positive feedback
How is GnRh secreted from the tonic and surge center?
In a pulsative manner
During post puberty what is the optimal time of tonic pulses for activation of LH and FSH secreting cells?
60-90min
WHat kind of GnRH pulses are found pre-puberty?
Less frequent so there is minimal stimulation of LH and FSH and minimal production of sex hormones
What is the sensitivity of the hypothalamus before puberty?
Very sensitive to feedback
What is the sensitivity of the hypothalamus after puberty?
Sensitivity to negative feedback decreases and increases release of more sex steroid hormones
What generates the Pulsative GnRH release?
KNDy
Are KNDy neurons sensitive to estrogen/testosterone negative feedback?
Yes, before puberty it is very strong, after puberty the strength of the negative feedback decreases and activates the pulse generator
Why is timing of puberty important?
Can effect productivity depending if the animal is a seasonal breeder
What factors can modify time of puberty?
- Genetics
- Nutrition
- Environmental and social cues
Why is nutrition so important in female puberty onset?
There is high need for energy when undergoing pregnancy so body must first have a large enough energy store to undergo
What nutrition factors are important for the onset of puberty?
- Leptin signaling from adipocyts
- IGF-1
- Blood glucose
- Blood fatty acid levels
