Flashcards in Puberty Deck (37):
What increases in males when puberty begins?
% motile sperm
% sperm with normal morphology
What increases in females when puberty begins?
fertility increases sometime after the first ovulation
What is puberty really?
a reactivation of the hypothalamo-pituitary-gonadal axis
What happens during the juvenile state that is different from puberty?
the hypothalamo-pituitary-gonadal axis is held in check by suppression of GnRH secretion from the hypothalamus
times the genetic program for puberty and sets a lower age limit on its occurrence
-provide signals to the developmental clock that may delay puberty if they are limiting
-if signals are not limiting, they cannot advance puberty earlier than the genetically preset lowest age
Where does the critical change for puberty occur?
hypothalamus; increase in frequency of GnRH pulses
Direct drive hypothesis
steroid-independent increased drive for GnRH secretion
(glutamate is most important stimulant, GABA is most important inhibitory)
(is the initial event decline in inhibition or increase in stimulation?)
secretin of GnRH during juvenile period is kept in check by negative feedback inhibition from gonadal steroids, but in puberty the sensitivity of the hypothalamus to the steroid feedback is changed
Explain what happens in female puberty in regards to GnRH
hypothalamus sensitivity to steroid feedback decreases, GnRH secretion increases, pituitary increases FSH and LH release, and full follicular development in the ovaries can occur
Initiation of puberty is most closely tied to what?
body growth rather than chronologic age
(making the developmental clock wait until the permissive signals are achieved is a protective mechanism)
What happens if you restrict dietary intake
retards growth and delays the time of puberty
How does photoperiod affect puberty?
seasonal breeders can only attain puberty within the breeding season
The interaction of these two factors will determine whether puberty is achieved for those animals that follow photoperiods
1. growth rate
2. their time of birth in the previous spring
How does time of birth affect puberty?
decides how much time they have to achieve the necessary target growth to initiate puberty
How does growth rate affect puberty?
determines how long it takes to achieve the target growth to initiate puberty
How do food supplies affect puberty?
seasonal variation in nutrition influence growth rate and thus the achievement of the metabolic gate
Name some social factors in attainment of puberty?
hastening of puberty on exposure to males
Explain how sex differences affect puberty
-there are sexually imprinted differences in the controls over GnRH secretion
-testosterone removes the strict requirement for photoperiod alternations and thus puberty can occur earlier in males
What is anestrus?
absence of estrus or the absence of cyclicity
prior to puberty the animal is acyclic
in periods of nutritional stress and poor body condition, cyclicity ceases
seasonal breeders will be anestrus in the non-breeding season
anestrus during lactation, varies between and within species
suppression of cyclicity relies on the daily frequency of suckling episodes by bonded offspring
suppression of cyclicity relies on energy balance
Explain hypothalamo-pituitary-ovarian physiology in the first two-thirds of pregnancy
progesterone is high and therefore the dominant follicles can't go through final maturation and ovulation
Explain hypothalamo-pituitary-ovarian physiology in late pregnancy
progesterone and estrogen levels are high, which suppress FSH so follicle waves no longer emerge and the ovary is quiescent
Explain hypothalamo-pituitary-ovarian physiology after pregnancy
progesterone and estrogen levels fall, removing inhibitory feedback and FSH release occurs
Why does suckling cause anestrus?
suckling of a bonded offspring causes release of maternal endogenous opioid peptides (EOPs) in the hypothalamus and these suppress GnRH neurons
What factors influence the time it takes a dairy cow to have her first ovulation after calving?
-poor body condition and low voluntary intake
-low feed intake and catabolizing large amounts of body tissue
-increased feed intake in high producing cows (causes low circulation of estrogen)
Improved energy balance results in what?
-central inhibition of GnRH is lifted, permitting increased LH
-increased insulin stimulates receptors for growth hormone on the liver and the somatotropic axis is restored
-dominant follicles can now fully mature and secrete sufficient estrogen to give an LH surge
The first ovulation following improved energy balance will likely be what?
a silent heat
What is senile anestrus?
when the number of primordial follicles falls below 1,000