MCDB 240: Puberty

Question 1

What are the three systems correlated w/ puberty?

Answer 1

Neuroendocrine axis, musculoskeletal, cardiovascular

Question 2

How many, and what are the requirements for puberty?

Answer 2

Hypothalamus, pituitary, functional gonads, adrenal glands, sex steroids?

Question 3

For males, FSH and LH influence which parts of the reproductive system?

Answer 3

Male: FSH infleunces Sertoli cells (sperm-producing cells)

LH influences testosterone producing cells (Leydig)

Question 4

Go over the entire female reproductive system.

Answer 4

Hypothalamus –> pituitary secretes both FSH and LH

–> FSH and LH secrete to growing follicle, which either induces estrogen OR ovulation –> uptick in estrogen at midcycle leads to LH surge, stimulates pituitary

–> LH only to corpus luteum, induces secretion of progesterone and SOME estrogen –> uptick post-ovluulation inhibits FSH and LH in both hypothalamus and pituitary

Question 5

Define gonadarche

Answer 5

Uptick in level of sex steroids from sex gonads; testes produce testosterone, ovaries produce estrogen

Question 6

what’s the driving force of pubertal changes

Answer 6

maturation of HPG axis

Question 7

define thelarche

Answer 7

breast development due to ovarian estrogen production

Question 8

define menarche

Answer 8

first menstrual bleeding

Question 9

define spermarche

Answer 9

initiation of sperm production

Question 10

define adrenarche/puberache

Answer 10

growth of public and axillary hair due to increased production of adrenal adnrogens at time of puberty, from the adrenals

Question 11

what do the ovarian estrogens influence?

Answer 11

affect breast development, development of genatalia, menarche, growth spurt

Question 12

what do testicular androgens influence?

Answer 12

development of male genatalia, body hair, enlarges larynx, extratesticular aromatization to estradiol

Question 13

is the HPG axis functional in a fetus

Answer 13

yes

Question 14

how to GnRH neurons develop in a fetus?

Answer 14

in the rostral forebrain at olfactory placode, migrate to arcuate nucleus and form GnRH pulse generator**

Question 15

when do the pulses start in a fetus?

Answer 15

11 weeks

Question 16

when are the highest levels of FSH and LH in a fetus?

Answer 16

20-30 weeks

Question 17

how is the pulse regulated?

Answer 17

negative feedback from pregnancy steroids?

Question 18

how high are the gonadotorpins levels in a fetus?

Answer 18

low

Question 19

what happens to the hormones levels at delivery?

Answer 19

abrupt withdrawal of maternal/placental hormones

Question 20

what happens to the GnRH pulse generator levels at delivery?

Answer 20

rebounds, leads to transient gonadal stimulation (neonatal breast budding, vaginal bleeding, milk secretion)

Question 21

in infants and children, what happens to the gonadotropin and sex steroids levels

Answer 21

decrease

Question 22

in infants and children, what are the GnRH pulse gen and gonadotropin levels?

Answer 22

both remain low, b/c of two hypotheses:

1) increased sensitivity of hypothalamus/pituitary to low steroids levels (neg feedback)
2) CNS inhibitor of GnRH (more likely, GABA)

Question 23

are there spontaneous FSH and LH pulses in children?

Answer 23

yes

Question 24

Puberty: what are the first signs

Answer 24

adrenarche, then first sign of gonadarche is increased amplitude and frequency of NOCTURNAL LH secretion

Question 25

increased ampl/freq of gonadotropin secretion during day and night is due to:

Answer 25

LH and FSH

Question 26

what are the two theories as to how puberty is activated?

Answer 26

gonadostat hypothesis: sensitivity of hypothalamus and pituitary to low levels of steroids falls at puberty (decreased negative feedback); gonadostat is the high sensitivity of hypothalamus/pituitary to circulating hormones levels CNS maturation: activation of hypothalamic GnRH secretion is driving force of puberty

Question 27

why is CNS maturation more likely than the gonadostat hypotheses?

Answer 27

b/c of rhesus monkeys castrated at birth still underwent puberty; they couldn't be sensitive to low levels of sex steroids b/c there were none. LH and FSH secretion patterns remained the same, female rhesus given GRH pulses via pump showed ovulatory menstural cycles

Question 28

prepubertal brake: define it

Answer 28

restraining of GnRH pulsatility at childhood and resumption of pulsatility at puberty

Question 29

what stimulates the GnRH neuron, what inhibits the GnRH neuron?

Answer 29

glutamate kisspeptin stimulates (puberty), GABA inhibits (childhood)

Question 30

what is the main determining factor of puberty? What is the proof?

Answer 30

GENETICS, as seen by female and male difference, racial differences

Question 31

what does the earlier onset of puberty suggest?

Answer 31

improve nutrition, changes in body weight, increased prevalence of obesity; malnutrition = delayed menarche; there is a need for critical body weight or composition (fat %)

Question 32

recap puberty in males and females: what are the physiological changes?

Answer 32

females: thelarche, adrenarche (may precede thelarche), menarche, ovluation male: testicular volume increases, penile growth, public --> axillary --> facial hair, ejaculation and spermarche

Question 33

go over adrenarche in females

Answer 33

- different from gonadarche - dependent on adrenal glands - progressive increase in plasma conc of adrenal androgens (DHEA/S) - occurs around 8 years of age

Question 34

go over pubarche in females

Answer 34

1) prepubertal 2) few coarse dark hairs 3) dark curly hair over mons pubis 4) adult hait, limited to mons 5) lateral distribution

Question 35

go over thelarche in females

Answer 35

1) prepubertal 2) budding: nipples and areolae enlarge and elevate 3) breast mounds form 4) areolae forms secondary mound on breast mound 5) adult contour, areolae recesses to breast contour

Question 36

go over menarche in females

Answer 36

- 10-16 years of age - pos feedback from estogen --> pituitary and hypothalamus --> midcycle LH surge --> ovulation - ovlution occurs w/i 6-9 months of mernarche - regular ovulatory cycles w/i 1-2 years of mernarche

Question 37

go over the entire process of puberty in a female w/ associated hormones

Answer 37

breast budding (E2) --> sexual hair growth (androgens DHEA/S), growth spurt (GH, E2), --> menarche (E2) --> adult breast (P) --> adult sexual hair (androgens)

Question 38

go over testicular enlargement in males

Answer 38

- due to enlargement of tubules due to testosterone, adult size reached w/i 4 years - penile elongation starts within 1 year of ball growth

Question 39

go over sexual hair growth in males

Answer 39

pubic hair appears 6 months after initiation of testicular enlargement, then axillary hair 18 months after pubic, then facial hair complete by 20 years of age (lateral corners of lips -> midline (T3) -> sideburns and chin hair (T5)

Question 40

go over spermarche in males

Answer 40

first ejaculations have no spermatozoa, just seminal plasma; Tanner 3 stage is when motile spermatozoa is found; conscious ejaculation indicates full capacity

Question 41

go over the process of puberty in males with associated hormones

Answer 41

testicular enlargement (T) --> pubic hair (androgens and T) -> penile enlargment (T), growth spurt (GH + E2), axillary hair (androgens and T), -> ejaculation (T) -> facial hair (T)

Question 42

go over growth spurt and how males differ so much from females in terms of height

Answer 42

three stages to growth spurt: 1) minimum growth velocity 2) peak growth velocity 3) decreased velocity and cessation at epiphyseal fusion disparity: males testosterones kicks in 2 years later than female estrogen; 2 more years go grow prior to spurt

Question 43

define bone age and why is it important

Answer 43

based on changes in ossification and epiphyseal fusion; correlates better w/ secondary sexual development than chronological age