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
