Puberty Flashcards
What is the major difference between a male and female hypothalamus?
Males don’t have a surge center
Why does the male hypothalamus not have a surge center?
Testosterone defeminizes it and eliminates the surge center.
*NOTE: It is actually estradiol converted from testosterone that defeminizes
Why doesn’t the estradiol produced by females also eliminate the surge center?
Because it’s bound to alpha-fetoprotein and cannot cross the BBB.
How is puberty started?
GnRH at the right frequency stimulates gonadotropin release by the anterior pituitary.
What 3 things does puberty promote?
Gametogensis
Steroidogenesis
Development of reproductive tissues
Define sexual maturity.
Age at first ovulation
Define breeding maturity.
Age where a female can support pregnancy without problems.
What are 3 signs of puberty in a male?
Behavioural traits expressed
Age at first ejaculation
Age when first spermatozoa appear in ejaculate or urine
What is the average age for bovine puberty?
11 months
What is the average age for ovine puberty?
7 months
What is the average age for porcine puberty?
7 months male, 6 months female
What is the average age for equine puberty?
14 months male, 18 months female
What is the average age for caprine puberty?
6 months
What is the average age for canine puberty?
6-12 months average (breed and size affects age)
What is the average age for feline puberty?
5-9 months (freed and photoperiod affects age)
What is the average age for llama puberty?
2-4 years, don’t usually breed until 3 years
What is onset of puberty NOT limited by?
Potential performance of gonads.
NOTE: prepubertal animals given exogenous GnRH will produce LH and FSH resulting in ovaries producing follicles and estradiol.
What is the major limiting factor of puberty?
Failure of the hypothalamus to produce sufficient quantities of GnRH.
What happens to the GnRH pulse frequency from the tonic center in the female after puberty?
Increases
Where does the preovulatory GnRH surge come from?
The surge center
Roughly how long does it take for the pulse frequency to raise to achieve puberty?
About 2 months
Which hormone is low in the prepubertal female?
Estradiol
What does the low estradiol in a prepubertal female cause?
No stimulation of the surge center, thus no preovulatory surge of GnRH and therefore LH
How is the scretion of GnRH from the surge and tonic centers controlled?
Positive and negative feedback.
NOTE: Puberty will be initiated when GnRH neurons can respond completely to this feedback.
What neurons are similar in number, function and distribution within the hypothalamus in males and females?
GnRH neurons
What is the process by which a male reaches puberty?
Increased testosterone/estradiol gives negative feedback, then GnRH increases, LH and FSH increase.
Before puberty, what is the surge center responding to?
The positive feedback that comes from estrogen.
What hormone is low in the prepubertal female?
Estrogen
What hormone has a positive feedback to the surge center, but negative feedback to the tonic center?
Estrogen
What happens to the GnRH neurons in the tonic center?
Sensitivity goes down
What 4 main things does the development of the hypothalamic nuclei depend on?
Body size/composition
Environmental cues
Social cues
Genetics
What determines body size/composition?
Blood glucose and fatty acids.
NOTE: low levels = disruption of cycle
What species might season of birth and photoperiod affect onset of puberty?
Sheep
NOTE: Sheep require decreasing day length
What kind of social cues might affect onset of puberty?
Exposure to the male (eg. gilts exposed to a boar go through puberty sooner than sows in small and large groups).
