Postnatal Sexual Development & Puberty Flashcards
1
Q
What are the periods of the reproductive system?
A
- fetal period
- prepubertal period
- reproductive period
- senescence period
Cycle diagram: puberty -> cyclicity -> pregnancy -> post-partum & lactation -> cyclicity -> this repeats until reproductive senescence
2
Q
What is the fetal period?
A
- sex determination, differentiation, & tract development & growth
3
Q
What is the prepubertal period?
A
- further growth & development, preparation for adulthood
4
Q
What is the reproductive period?
A
- sexual activity resulting in conception & production of offspring is possible
5
Q
What is the senescence period?
A
- reproductive function is no longer possible
6
Q
How does hypothalamic development differ btwn females & males?
A
- key factor in differential sexual development of female vs male is ALPHA FETOPROTEIN (a-FP)
- in female embryos, a-FP BINDS E”2”, preventing it from passing the BBB & entering the brain, so hypothalamus is “FEMINIZED” & GnRH surge center develops
- in males, T freely enters brain since a-FP DOES NOT BIND T, so T in brain is aromatized into E”2” & hypothalamus is “DEFEMINIZED” & surge center does not develop
7
Q
How does LH secretion differ btwn males & females?
A
- pubertal females have high amplitude surges of LH every several weeks & pulsatile releases in btwn surges
- pubertal males have sm LH pulses every 2-6 hrs throughout. testosterone immediately follows each LH pulse.
8
Q
How does the secretion of GnRH change before and after puberty?
A
- before puberty in both males & females, GnRH neurons in both tonic & surge centers release low amplitude & low frequency pulses of GnRH
- after puberty in females, tonic center controls basal lvls of GnRH, but they are higher than in prepubertal females b/c pulse frequency increases. surge center controls preovulatory surge of GnRH
- males do not develop a surge center
9
Q
What is the prepubertal period?
A
- prepubertal is period btwn birth & puberty
- period of secondary sexual growth & development
- varies from a few days or weeks to several months or years, depending on spp
- divided into early-, mid-, late-prepubertal, & peri-pubertal stages
- in the second half of this period, the rate of growth for reproductive tract increases over general body growth
- somatic & behavioural secondary sexual characteristics appear
- culminates w/ ONSET OF PUBERTY
10
Q
What is the difference btwn puberty and maturity?
A
- sexual maturation, physical maturation, & fertility potential, all continue beyond onset of puberty
- puberty is defined differently in different spp & from different perspectives
- for animals, puberty = age @ which reproduction & parentage 1st becomes possible
- for humans, puberty = transition from childhood to adulthood
11
Q
When is the onset of puberty in female animals:
A
- age @ 1st estrus (most practical, although most 1st ovulations are silent)
- age @ 1st ovulation (scientifically more accurate, but less practical; requires frequent palpation, ultrasonography, or measuring progesterone twice weekly)
- age @ 1st attainment of ability to support pregnancy (can be a while after either 1st estrus or 1st ovulation; for dairy cattle it is usually based on acquisition of a threshold body size
12
Q
When is the onset of puberty in male animals:
A
- age when behavioral traits are expressed? - no (humping behaviours in puppies)
- age at first sperm produced? - sperm is produced quite a bit earlier than other signs
- age @ first ejaculate? - 1st ejaculate could or could not have sperm, in beginning sperm are not v good quality
- age when the ejaculate contains a threshold number of spermatozoa? (more practical & meaningful from a breeding standpoint; in bulls, minimum of 50 million sperm w/ @ least 10% motility; has a chance of achieving pregnancy but these numbers increase later)
13
Q
What factors affect the rate of sexual maturation?
A
- genetics
- nutrition
- season
- breed/race
- sexual/ social associations
- environmental influences
- general health
- endocrine disruptors
14
Q
How does genetic /spp variation affect the rate of sexual maturation?
A
- great variation among different spp
- even among a spp, ~50% of variations are due to genetics
15
Q
How does breed/race affect the rate of sexual maturation?
A
- breeds w/in spp can vary greatly in age @ puberty
- genetic selection & geographical locations have affected age @ puberty
- variations also seen among human races, African-American girls reach puberty earlier (mean 12 yr; ~50% by age 9 vs. ~12% Caucasians)
- this mean age is 18 yr for girls in some tribes in high altitude regions in Asia
16
Q
How does nutrition affect the onset of puberty in dairy heifers?
A
- age @ 1st parturition should be 24 months & weight 1200 lb
- nutrition is believed to be also a main source in reduction of age @ puberty in human populations
- overweight kids reach puberty earlier
- for each decade for >100 years, the age at puberty has dropped by 4 months
17
Q
What is the effect of growth rate & male exposure on age at puberty?
A
- growth rate & bull exposure both decrease age @ puberty in beef heifers
- similarly in human populations, girls exposed to older males reach puberty earlier
18
Q
How does group size & male exposure influence the age at puberty?
A
- larger groups reduce age at puberty
- effect of male exposure can be stronger than group size
- effect of male exposure on reducing age @ puberty does not have to be physical; visual or olfactory cues are sufficient
- girls living in dorms may have synchronized periods
- role of pheromones cannot be ruled out
19
Q
How does season of birth influence the age of puberty?
A
- for seasonal breeders, age @ puberty is strongly influenced by season of birth
- spring-born ewe lambs reach puberty @ a much younger age but less synchronously
- fall-born ewe lambs take much longer time to reach puberty but are more synchronous
20
Q
How does glucose affect GnRH release?
A
- in OVX ewe lambs, low amplitude LH pulses occurred hourly before treatment with 2-deoxyglucose (2DG - is a glucose oxidation inhibitor -> more glucose in the bloodstream, not being oxidized into cells)
- LH frequency & amplitude dropped after treatment
- but LH still could respond to exogenous GnRH
- so moment-to-moment regulation of GnRH happens when glucose is available
21
Q
How do metabolism signals potentially effect GnRH?
A
blood glucose, fatty acids, & leptin levels, as indicators of nutritional & metabolic status, stimulate kisspeptin neurons that in turn stimulate GnRH neurons
22
Q
How is puberty regulated by the endocrine system?
A
- gonads, pituitary, or even capacity to produce GnRH are not the limiting factors
- lack of high frequency & amplitude GnRH pulses is key
- role of an oscillator, GnRH pulse generator
- puberty depends on reactivation of GnRH secretion
23
Q
What leads to the release of GnRH?
A
- gonadostat theory
- removal of other central inhibitors: ex: opioids, gamma amino butyric acid (GABA)
- activation of a central driver: ex: NE, excitatory AAs, neuropeptide Y, kisspeptin
24
Q
What is the gonadostat theory?
A
- before puberty, hypothalamus is highly sensitive to negative feedback of E”2” & GnRH will not be released even w/ low lvls of E”2” present
- high lvl of estrogen receptors (ER) are present @ this time in the hypothalamus
- during the transition to puberty, negative sensitivity of the hypothalamus to E”2” is reduced, allowing higher release of GnRH
- lvls of hypothalamic ER are also reduced
25
How do we know that the hypothalamus is sensitive to estradiol before puberty?
- OVX causes LH pulses to be presents @ a similar frequency as in adults
- replacing E"2" in OVX animals prevents LH pulses during the 1st part of the prepubertal period
26
What are the hypothalamic E"2" receptor levels in a prepubertal animal?
high
27
What are the hypothalamic E"2" receptor levels in an early peripubertal animal?
medium
28
What are the hypothalamic E"2" receptor levels in a peripubertal animal?
low
29
What are the hypothalamic E"2" receptor levels in a pubertal animal?
varies
30
What is the E"2" feedback on LH in a prepubertal animal?
strongly negative
31
What is the E"2" feedback on LH in an early peripubertal animal?
less negative than in prepubertal animal
32
What is the E"2" feedback on LH in a peripubertal animal?
less negative than in an early peripubertal animal
33
What is the E"2" feedback on LH in a pubertal animal?
positive (when estradiol lvls pass a certain threshold, it then becomes positive feedback; follicle becomes so big it bursts open)
34
What are the E"2" levels in a prepubertal animal?
low
35
What are the E"2" levels in an early peripubertal animal?
low
36
What are the E"2" levels in a peripubertal animal?
medium
37
What are the E"2" levels in a pubertal animal?
high
38
What is the LH secretion pulse frequency in a prepubertal animal?
low
39
What is the LH secretion pulse frequency in an early peripubertal animal?
slight increase from prepubertal
40
What is the LH secretion pulse frequency in a peripubertal animal?
increasing from early peripubertal
41
What is the LH secretion pulse frequency in a pubertal animal?
LH surge observed
42
What is the reproductive tract score (1 = low development, 5 = high) in a prepubertal animal?
1
43
What is the reproductive tract score (1 = low development, 5 = high) in an early peripubertal animal?
2
44
What is the reproductive tract score (1 = low development, 5 = high) in an peripubertal animal?
3
45
What is the reproductive tract score (1 = low development, 5 = high) in an pubertal animal?
4 or 5
