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CMHC201 > Lecture 19: Biology of Puberty > Flashcards

Lecture 19: Biology of Puberty Flashcards

1
Q

what is puberty?

A

puberty is the time of development when the body undergoes changes to become fully reproductively capable

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2
Q

what 3 things happen during puberty?

A
  • production of sex hormones
  • maturation of reproductive organse
  • secondary sex characteristics
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3
Q

what secondary characteristics happens to females during puberty?

A
  • breast development
  • pubic hair
  • broadening of hips
  • increase and change in fat distribution
  • growth spurt
  • menstruation
  • axillary hair
  • acne
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4
Q

what secondary characteristics happens to males during puberty?

A
  • testicle and penis growth
  • pubic hair
  • growth of muscle
  • growth spurt
  • voice deepens
  • night time emissions (wet dreams)
  • axillary hair
  • acne
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5
Q

what is pubarche?

A

appearance of pubic hair

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6
Q

what is adrenarche?

A

increased production of androgens from adrenal gland

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7
Q

what is thelarche?

A

early breast development

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8
Q

what is manarche?

A

first menstruation/period

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9
Q

when does puberty happen?

A

girls - 8-13
boys - 9-14

early puberty - “precocious”
late - “delayed puberty”

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10
Q

how is puberty development measured?

A

by physical changes/tanner stages

the scale divides puberty into 5 stages based on:

M: pubic hair and genitalia
F: pubic hair and breasts

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11
Q

what is the timing of puberty for males and females?

A

puberty is a time of rapid growth:

  • gain between 25-28cm in height
  • boys start growth 2 years later than girls
  • ends with fusion of long bone growth plates
  • boys start puberty later than girls
  • marache is about 2 years after breasts start to develop and does happen till the later tanner stages
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12
Q

what is the brain development during puberty?

A

teenagers are risk taking and impulsive but poor judgement

  • the brain is still pruning
  • based on environment/experiences
  • continues until early 20s
  • area of the brain associated with evaluating risk and reward is still developing
  • area associated with emotion, regulation, long term planning is still developing
  • grey matter (cell bodies, dendrites, axon terminals which is where synapses are) decreases from back to front as neural synapses are pruned
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13
Q

what are the sex differences in brain development?

A

males have increased connectivity
females have decreased connectivity

maturity is associated with decreased connectivity which indicates why it is thought the females mature earlier than males

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14
Q

what drives the biological changes seen in puberty?

A

increases in estrogens (estradiol) and androgens (testosterone)

  • they are secreted from cells in the ovaries and testes
  • they drive the development of secondary sex characteristics
  • act on reproductive organs (testes and ovaries) to be capable of reproducing
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15
Q

what causes the increase of sex steroid production during puberty?

A

the endocrine system feedback loop!

GNrH neuron in hypothamalmus releases GnRH into pituitary gland which secretes LH and FSH which acts on the gonads which release estradiol, progesterone and testosterone which then have their effects in the body.

these 3 hormones act back on the hypothalamus and pituitary to inhibit further secretion of the 3 hormones. Regulate their own stimulation to keep hormones at the right level.

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16
Q

what stimulates the GnRH neurons during puberty?

A
  • in it hard to measure GnRH secretion levels
  • but studies have found that secretion of LH mimics the secretion of GnRH
  • we know that LH rapidly increases during puberty and is supressed during childhood, this is also seen with GnRH
  • but what activates GnRH?
17
Q

what is the history of kisspeptin?

A

in 1996 scientists in hershey discovered a gene that suppressed metastatic tumour growth. because of this gene the gene was inferred to code a suppressor sequence. it was called Kiss1

in 2001 3 groups reported that the ligands for G-protein coupled receptor 52 (GPR54, aka kiss1) were the kisspeptin family peptides

another study came out showing that the GPR54 and kisspeptin interaction was vital for puberty to start

18
Q

what does kisspeptin do?

A

kisspeptin is the most potent activator of GNRH neurons discovered so far

  • many studies have been done which showed that GnRH increases as soon as kisspeptin was given
19
Q

what does this show about kisspeptin during puberty?

A

these are a coronal brain section at level of hypothalamus

black staining = kisspeptin

before puberty there is little to no kisspeptin present, but in adulthood there is a lot of kisspeptin.

kisspeptin activated GnRH which goes on to continue the endocrine feedback loop (mentioned in previous card)

20
Q

what triggers puberty?

A

we dont know :(

21
Q

what things can affect the timing of puberty?

A
  • genetics
  • body weight/nutritional status
  • stress
  • environment
22
Q

how does genetics impact the timing of puberty?

A
  • timing of puberty is inheritable
  • 50-80% of variation in the timing of puberty is under genetic control (e.g. identical twins and 2.2 month difference in menarcheal age, while unrelated women had 18.6 months difference)
  • pubertal onset varies between ethnic groups (by age 11 29% pacific girls attained menarche but only 8% of NZ european girls did)
  • genetic studies have shown a range of genetic variations associated with the timing of puberty. such as in production of GnRH, development and function of pituitary, bioactivity of hormones, energy homeostasis
23
Q

how does body weight/nutritional status impact timing of puberty?

A

(overlaps with genetics)

  • high energy requirements are required for changes in puberty and successful reproduction (especially in females)
  • underfed children can have delayed puberty, overweight children can have earlier puberty
  • old 1960’s hypothesis thought that there is a ‘critical fat mass’ which is essential for puberty to start. but how does the body know how much fat you have?
  • in 1994 leptin was discovered, which is a hormone secreted in proportion to size and number of fat cells in the body. leptin is needed to go through puberty, if it is too low puberty won’t start.
24
Q

what are some metabolic puberty ‘alarm clocks’?

A

things that can awaken GnRH neuron at puberty:

  • leptin
  • insulin
  • IGF-1
  • irisin
25
Q

how does leptin work in puberty?

A
  • leptin comes from fat
  • has indirect actions on GnRH neurons
  • thought to stimulate kisspeptin neurons which stimulates GnRH neurons.
26
Q

how does insulin work in puberty?

A
  • insulin levels increase as puberty progresses
  • possibly has direct actions on GnRH neuron
  • insulin has an important input to GnRH through astrocytes
    (astrocytes act on GnRH)
27
Q

how does IGF-1 work in puberty?

A
  • IGF-1 is modulated by nutritional status
  • has possible direct actions on GnRH neurons
  • also stimulate kisspeptin neurons
  • 2 way effect!
28
Q

how does irisin work in puberty?

A
  • is a hormone secreted from muscle in response to exercise
  • increases during puberty
  • however animal studies suggest irisin delays puberty
  • more work needed.
29
Q

how does stress affect the timing of puberty?

A

in adults, HPG axis is senstive to stress
- stress hormone ‘cortisol’ is secreted by the adrenal gland

  • there are physical stressors and emotional/psychological stressors which can impact puberty (such as war situations?)
  • timing of stress has different impacts on puberty:
  • stress in earlier childhood associated with earlier menarche
  • stress just before puberty or during puberty associated with later menarche
  • chronic illness associated with delayed puberty
  • mechanisms of how stress effects puberty likely depends on type of stress and timing of stressor.
30
Q

explain the mechanisms of stress on puberty.

A

HPA axis = stress feedback loop

CRH act on hypothalamus which acts on pituitary to release ACTH which acts on adrenal glands which then secretes glucocorticoids (cortisol)

  • if this loop is activated for a long time high levels of CRH and glucocorticoids can inhibit the activation of GnRH neurons in the HPG axis which can then impact reproduciton
31
Q

how can environmental factors impact the timing of puberty?

A

endocrine disrupting chemicals (EDC) are natural and man made chemicals that can mimic or interfere with the body’s hormones

e. g. - phytoestrogens are found in plastics, pesticides and foods which mimic the actions of estrogen which can advance puberty onset.
- location also plays a part: children who live near the equator go through puberty earlier than children who live closer to the north/south poles.

32
Q

why does location impact timing of puberty?

A

likely because of melatonin!

  • melatonin is produced in response to darkness
  • is important for circadian rhythms and sleep
  • also peaks at night!

nocturnal levels of melatonin decrease across puberty

Melatonin Theory:
- so decreasing levels of melatonin lead to increased kisspeptin to stimulate GnRH activation in puberty

those who live near equator have longer nights.

33
Q

what trend have we seen about puberty timing in the last 100 years?

A
  • age of menarche has been dropping overtime
  • thought to be due to better public health and access to better food and increased body weight
34
Q

what are the proposed causes of early precocious puberty?

A

(before age of 8 in girls/9 in boys)

  • increased BMI (linked to leptin levels)
  • genetic
  • reduced melatonin
  • stress/sub-optimal environment
35
Q

what are the proposed caused of delayed puberty?

A

no signs by 13 years for girls, 14 for boys

  • low weight/body fat
  • genetic
  • hypogonadism (lack of gonad hormones)
  • abnormalities of the pituitary gland
36
Q

what are the health impacts of earlier puberty in females?

A

increased risk of developing:

  • breast and endometrial cancer
  • obesity
  • type 2 diabetes
  • cardiovascular
  • depression and anxiety
37
Q

what health impacts does puberty timing have?

A

both earlier or later puberty timing in women or men was associated with higher risk of 48 adverse outcomes including:

  • various cancers
  • cardio-metabolic disease
  • gynaecological/obstetric issues
  • gastrointestinal issues
  • musculoskeletal issues
  • neuro-cognitive problems

CMHC201 (15 decks)

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