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Physiology 2 > Puberty (repro) > Flashcards

Puberty (repro) Flashcards

1
Q

What is puberty?

A
  • Transition from non-reproductive to reproductive state
  • Gonads produce. mature gametes (testes to spermatozoa, ovaries to oocytes)
  • Breast development in females
  • Increased testicular volume in males
  • Secondary characteristics develop (primary present at birth)
  • Profound physiological changes
  • Profound psychological changes
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2
Q

2 Endocrine events of puberty

A 
Adrenarche:
- adrenal androgens 
- growth of pubic hair (axillary hair)
- growth in height 
- independently regulated
Gonadarche:
- LH leads to steroid synthesis and secondary sex characteristics 
- FSH leads to growth of testis (male) and steroid synthesis/folliculogenesis (female)
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3
Q

Adrenarche

A
  • Change in adrenal androgen secretion due to cellular remodelling of adrenal gland
  • Dehydro-epiandrosterone (DHEA) and dehydro-epiandrosterone sulphate (DHEAS) steroid hormones influence adrenarche
  • Gradual increase of hormones from age 6-15 years
  • 20 fold increase peaking at 20-25 years
  • Declines thereafter
  • No change in other adrenal steroids
  • Secreted from zona reticularis of adrenal cortex
  • No known mechanism for trigger of adrenarche
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4
Q

Pubarche

A
  • Appearance of. pubic/axillary hair resulting from adrenarche (adrenal androgen secretion)
  • Associated with increased sebum production, infection and abnormal keratinisation, resulting in acne
  • If signs are present before 8yrs old (girls) and 9yrs old (boys), they are known as precocious
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5
Q

Gonadarche

A
  • Several years after adrenarche
  • typically around 11yrs old
  • Reactivation of hypothalamic GnRH
  • Activation of gonadal steroid production leads to production of viable gametes and ability to reproduce
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6
Q

GnRH

A
  • GnRH is synthesised and secreted by specialist hypothalamic centres (GnRH neurons)
  • HPG axis is first activated at 16th gestational week
  • Pulsatile GnRH secretion in foetus until 1-2 years postnatally then ceases
  • Reactivation at 11yrs
  • GnRH neurones restrained during postnatal period (10yrs plus)
  • At puberty, a gradual rise in pulsatile release of. GnRH
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7
Q

What stimulates the onset of puberty?

A

Potentially:

  • Inherent (genetic) maturation of 800-1000 GnRH synthesising neurones
  • Environmental/genetic factors
  • Body fat/nutrition
  • Kisspeptin
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8
Q

Nutrition and body fat

A
  • Link between fat metabolism and reproduction
    Anorexia nervosa/intensive physical training:
  • reduced response to GnRH
  • reduced gonadotrophin levels
  • amenorrhea
  • restored when nourished/exercise. stopped
    Body fat hypothesis (Frisch et al.):
  • Certain % fat:body weight necessary for menarche (17%) and required to maintain female reproductive ability (22%)
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9
Q

Kisspeptin and puberty

A

Inactivating mutations of KISS1R or the genecodinf for kisspeptin:

  • Hypogonadism
  • Failure to enter puberty
  • Hypogonadotrophic hypogonadism

Activating mutations of KISS1R:
- precocious puberty

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10
Q

What is consonance?

A
  • Order of pubertal changes is uniform
  • Age of onset, pace and duration of changes are uniform
  • Wide inter-individual differences
  • Average age of menarche onset is 12.5yrs old (UK)
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11
Q

Tanner stages of puberty

A
  • 5 stages of growth for 3 areas:
  • breast development (girls)
  • genital development (boys)
  • pubic hair development (both)
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12
Q

Physical changes during puberty (girls)

A
  • Breasts enlarge (thelarche is first outward sign of E2 activity)
  • Pubic/axillary hair
  • Uterus enlarges, cytology changes and secretions in response to E2
  • Uterine tubes
  • Vagina
  • Cervical changes
  • Height (earlier onset than boys, peak height velocity PHV is 9cm/y, reached at 12yrs)
  • Body shape
  • HPG axis (increase in ovarian size and follicular growth)
  • Menarche/menustration (not equated with onset of fertility
  • Fertility (in 1st yr, approx 80% menstrual cycles are anovulatory or irregular)
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13
Q

Physical changes during puberty (boys)

A
  • External genitalia (increase in testicular volume, more than 4ml), (growth of penis, scrotum and scrotal skin changes)
  • Vas deferens (lumen increases)
  • Seminal. vesicles and prostate
  • Facial/body hair
  • Pubic/axilllary hair
  • Larynx enlarges (due to androgens, Adams apple forms due to projection of thyroid cartilage, and voice deepens)
  • Height (PHV is 10.3cm/y reached at 14yrs)
  • Body shape
  • Onset of fertility (testosterone from leydig cells stimulates meiosis and spermatogenesis in Sertoli cells), (boys fertile at beginning of puberty)
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14
Q

Growth spurt

A
  • Complex interaction of growth hormone and oestrogen
  • Earlier in girls (approx 2yrs)
  • Biphasic effect of oestrogen on epiphyseal growth:
  • low levels result in linear growth and bone maturation
  • high levels result in epiphyseal fusion
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15
Q

Psychological changes

A
  • Increasing need for independence
  • Increasing sexual awareness/interest
  • Development of sexual personality
  • Later maturation leads to better. adjustment
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16
Q

Disorder: precocious sexual development

A
  • Development of any secondary sexual characteristics before 8yrs in girls and 9-10yrs in boys
  • Premature activation of HPG axis can cause 2 disorders:
    1) Gonadotrophin-dependant precocious puberty (consonance):
  • excess GnRH secretion (idiopathic or secondary)
  • excess gonadotrophin secretion which could result in a pituitary tumour
    2) Gonadotrophin-independant precocious puberty (loss of consonance):
  • testotoxicosis (activating mutation of LH receptor)
  • sex steroid secreting tumour or exogenous steroids
  • example: McCune Albright syndrome is a mutation in the GNAS1 gene, affecting autonomous endocrine function causing hyperactivity of signalling pathways and overproduction of hormones, resulting in cafe au lait skin pigmentation and fibrous dysplasia
17
Q

Disorder: pubertal delay

A
  • Absence of secondary sexual maturation by 13yrs (or absence of menarche by 18yrs) in girls or by 14yrs in boys
  • Delayed HPG axis activation can cause 3 disorders:
    1) Constitutional delay:
  • affecting both growth and puberty (approx 90% of all pubertal delay cases)
  • Around 10x more common in boys
  • Secondary to chronic illness, eg diabetes, cystic fibrosis
    2) Hypogonadotrophic hypogonadism:
  • low LH and FSH
  • Kallman’s syndrome (X-linked KAL1 gene, impaired GnRH migration)
  • Other mutations causing defects in GnRH production
    3) Hypergonadotrophic hypogonadism:
  • High LH and FSH
  • Gonadal dysgenesis and low sex steroid levels
  • gonadal dysgenesis with normal karyotype, viral eg mumps
  • Gonadal dysgenesis resulting from abnormal karyotype, eg Klinefelter’s syndrome XXY, Turners syndrome X0
18
Q

Summary

A
  • 2 independently regulated events culminate in puberty which are adernache and gonadarche
  • Adernache is result of activation of adrenal androgen secretion
  • Gonadarche is result of reactivation of hypothalamic GnRH
  • Physical changes associated with puberty are measured using the Tanner scale
  • Consonance is the smooth, ordered progression through Tanner stages
  • Precocious puberty is the development of any secondary sexual characteristic before the age of 8yrs in girls or 9-10yrs in boys
  • Delayed puberty is absence of secondary sexual maturation by 13yrs (18yrs absence of menarche) or 14yrs in boys
19
Q

Glossary

A
  • Adrenarche: The first endocrine event of puberty. It is the result of cellular maturation of the adrenal gland, which results in the increase in DHEA/DHEAS production. This usually occurs approximately 6-8 years of age and is independently regulated from gonadarche.
  • Gonadarche: The second endocrine event of puberty. The ‘re-awakening;’ of the HPG axis, initially presenting as a nocturnal rise in GnRH (measured via LH), and results in the initiation of fertility.
  • Tanner Stages of Puberty: Five stage scale of puberty, originally developed by the paediatric endocrinologist, James Tanner. It describes the physical changes in breast development (females), hair development and external genitalia, with the first stage of puberty being breast budding in females, and an increase in testicular volume > 4ml in males.
  • Consonance: The completion of each stage of puberty in the correct order, as denoted by the Tanner Stages of Puberty, known as the ‘smooth ordered progression’. The time that individuals take to go through each stage may differ, but the order in which the stages are completed remains the same between individuals.

Physiology 2 (38 decks)

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