The onset of reproductive activity Flashcards
What is puberty in humans (menarche)
The point of first menstruation/ point of carrying offspring to first term
What is puberty in animals
The ability to accomplish reproductive successfully
What is pre-pubertal
Hypothalamic neurones and HPG established but quiescent
Peri-pubertal
Acquire ability to receive information from pre-synaptic
neurones to increase frequency and promote GnRH secretion
Puberty
Increased frequency and amplitude of GnRH secretion
What is brain puberty dependent on?
ability of hypothalamus to secrete sufficient GnRH to stimulate pituitary gonadotrophin secretion.
When is brain puberty stimulated?
Stimulated when GnRH neurones respond completely to gonadal hormone feedback.
What happens to light as it enters the eye?
RHT goes to synapses at the SCN this then travels to the ganglion of the neck then back to the pineal gland
When is melatonin secreted?
during hours of darkness
When is the hypothalamus sensitive to melatonin?
during the late afternoon
What indicates a short day?
coincidence of melatonin secretion and hypothalamus sensitivity
What is puberty dependent on?
body mass and fatness
What does 2-deoxyglucose do?
inhibits glucose oxidation which supresses pulse frequency/ LH
When would an animal start laying down fat reserves?
After all essential body systems have been produced
What is a trigger for puberty?
Fat reserves
How does leptin trigger GnRH secretion?
leptin acts on neuropeptide Y neurons which acts on kisspeptin neurons which acts on GnRH neurons and therefore GnRH is released
What is the effect of GnRH during Pre-Puberty in females?
The hypothalamus releases small amounts of GnRH which in turn releases small pulses of LH and FSH and smaller amounts of estrogen which acts negatively on the hypothalamus to decrease pulse frequency
What is the effect of Maturation in a pubertal female?
Once the Hypothalmus matures there is increased pulses of GnRH and therefore increased pulses of LH and FSH, this stimulates follicles to mature and causes more oestrogen to be produced which has a positive effect on the hypothalamus and causes the surge centre to cause ovulation
What do low levels of estrogen mean for the centres in a female?
It means negative feedback which causes decreased pulsing in the tonic centre
What do higher levels of estrogen due to follicles mean for the centres in a female?
It means positive feedback which will stimulate the surge centre
When is melatonin released?
In the absence of daylight
What would signify a short day to an animal?
If melatonin secretion coincided to when the hypothalamus is most sensitive to melatonin (around 4pm)
What is the pathway that secretes melatonin?
Stimulus of light-> travels along the retino-hypothalamic tract -> synapses at the SCN -> BSCG -> synapses at the SCN again -> pineal gland -> conversion of tryptophan into serotonin and serotonin into melatonin
What proves that brain puberty is independent of the anterior pituitary?
You can induce puberty at any point by injecting GnRH
