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sor > Lecture 5: Puberty > Flashcards

Lecture 5: Puberty Flashcards

1
Q

What is the definition of puberty? (reproductively and clinically)

A

(Complex developmental event)
- Continuum of changes leading to somatic and sexual maturation
- Profound physiological, psychological and physical changes

(Reproductively - To produce mature gametes:)
- Testes= production of spermatozoa
- Ovaries= development of meiotically competent oocyte

(Clinically)
- Breast development in females, and increased testicular volume in males

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2
Q

What are the endocrine events of puberty?

A
  • Adrenarche
  • Gonadarche
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3
Q

What is adrenarche and how is it clinically presented?

A
  • activation of adrenal androgens (dhea/s)
  • associated with:
    - growth of pubic hair,
    - axillary hair
    - growth in height.
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4
Q

Definition of gonadarche

A
  • Activation of HPG axis to produce and secrete LH/FSH
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5
Q

What do the 2 gonadotrophin hormones cause in gonadarche?

A

LH: steroid synthesis -> secondary sex characteristics

FSH: growth of testes; steroid synthesis; folliculogenesis

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6
Q

Is adrenarche and gonadarche dependent on one another?

A

-No, they are independently regulated

i.e. one does not cause the other and one does not have to start for the other to start too.

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7
Q

Which endocrine process of puberty is first?

A
  • Adrenarche
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8
Q

At what age does adrenarche occur?

A
  • 6-8 years
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9
Q

What is adrenarche characterised by? / which hormones are reinstated?

A
  • re-instigation of adrenal androgen secretion:
    • Dehydrogenase-epiandrosterone (DHEA)
    • Dehydrogenase-epiandrosterone sulphate (DHEA-S)
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10
Q

What changes occur in adrenarche hormonally?

A
  • DHEA and DHEA-S secretion
  • No change in cortisol/other adrenal hormones
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11
Q

Is the HPA axis activated during adrenarche?

A
  • Yes, BUT not globally.
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12
Q

Where is DHEA and DHEA-S secreted from?

A
  • Zona reticularis
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13
Q

Anatomy of the adrenal gland

A
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14
Q

Why are DHEA and DHEA-S reinstated?

A
  • Inherent maturation of cellular compartments of the adrenal cortex
  • i.e. remodelling of the adrenal cortex
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15
Q

What happens to the adrenal gland during the foetal development stage and which hormones are present?

A
  • 2 zones only present: foetal zone and definitive zone
  • DHEA/S production
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16
Q

What happens to the adrenal gland during the neonate developmental stage and which hormones are present?

A
  • Involution of foetal zone (shrinkage of foetal zone)
  • DHEA/S production
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17
Q

What happens to the definitive zone during the infant developmental stage

A
  • Differentiates into zona glomerulosa and zona fasiculata
18
Q

At approx 3 years old, what changes are seen in the adrenal gland?

A
  • Focal islands of Zona reticularis present (ie patches of ZR beginning to form)
19
Q

At what age is the functional ZR developed and what hormones are present then?

A
  • approx 6 years
  • DHEA/S production
20
Q

What is the significance of the formation of the ZR?

A
  • DHEA/S production resumes and initiates adrenarche
21
Q

Does the ZR develop as one goes into puberty? And what age is this?

A
  • Yes, it continues to expand
  • Thus there is an increase in DHEA/S production
  • 12-13 years
22
Q

When does adrenal remodelling start in humans?

A
  • as a foetus
23
Q

Describe the characteristics of adrenal remodelling during development from foetus to 12-13 years of age

A
24
Q

Describe what you will see in the histology of the adrenal gland in an infant (pre-adrenarche)

A
25
Q

Describe what you will see in the histology of the adrenal gland in a pubertal child?

A
  • ZR developed as a result of remodelling
26
Q

How is DHEA/S made?

A
  • 3BetaHSD expression down-regulated during adrenarche
  • pathway with 3betaHSD shuts down
  • cholesterol able to fully commit to production of DHEA/S.
27
Q

Which enzymes have an increased expression during adrenarche

A
  • cytochrome b5
  • SULT2A1
28
Q

Which enzyme has a down-regulation in expression in the ZR during adrenarche

A
  • 3BetaHSD
29
Q

How do the adrenal androgens DHEA/S function?

A

-DHEA/S released from adrenal gland -> enter circulation -> enter peripheral tissue metabolism where they are converted to DHT

  • DHEA/S aid in prostrate secretion, pubic hair follicle
30
Q

What instigates adrenarche?

A
  • No conclusive mechanism for control and regulation of adrenarche
31
Q

Give examples of studies to test the instigation of adrenarche

A
  • ACTH: Dexamethosone (synthetic cortisol steroid) suppresses adrenal androgen production; children with ACTH receptor mutations fail to undergo adrenarche; NO CHANGE IN ACTH/CORTISOL DURING ADRENARCHE
  • POMC: Proximal 18 AA region that positively regulated adrenal androgen production; In vitro studies did not substantiate this
  • POMC-related peptides: b-lipotrophin and b-endorphin plasma levels correlate with increased DHEA/S at adrenarche BUT NO DIRECT LINKAGE
  • Other factors ruled out include prolactin, IGF-1 and insulin
32
Q

What is gonadarche?

A
  • The reactivation of HPG axis
33
Q

When does gonadarche occur?

A
  • Several years after adrenarche (typically ~11 yrs of age).
34
Q

What drives gonadarche?

A
  • Hypothalamic GnRH & pituitary gonadotrophins i.e. HPG axis
35
Q

What does puberty depend on?

A
  • Reactivation of GnRH release
36
Q

Describe the HPG axis

A

GnRH is synthesised & secreted
↓
Synthesis and secretion of pituitary gonadotrophins (LH & FSH)
↓
Gonadal steroid production
↓
Negatively/positively feedback onto hypothalamus-pituitary to regulate GnRH and LH/FSH production

37
Q

When is the HPG axis activated and shut down during ones lifetime?

A
  • 16th gestational week (pulsatile GnRH secretion in foetus) -> shut down just before birth
  • 1-2 years postnatally -> Neurones are then ‘restrained’ during postnatal period - 10 years or more
  • At puberty a gradual rise in pulsatile release- around 1 year before breast budding observed (secondary sexual characteristics)
38
Q

With your understanding of the HPG axis, what is gonadarche due to?

A
  • The reactivation of the HPG axis
39
Q

Describe GnRH levels prepuberty

A
  • constant low levels of GnRH
40
Q

Describe GnRH levels early-mid puberty

A
  • Nocturnal rise in GnRH (the study used LH as equivalent to GnRH) whilst asleep

(Nocturnal as in sleep-wake cycle - not time of day)

41
Q

Describe GnRH levels mid-late puberty

A
  • Pulsatility is consistent throughout
42
Q

Describe GnRH levels in adults

A
  • Well-established pattern
  • Cyclical pattern depending on which stage of the menstrual cycle you are on

sor (12 decks)

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