Puberty Flashcards
Define thelarche
The development of breasts
Define puberache
Development of axillary and pubic hair
Define menarche
The first menstrual period
Define adrenarche
The onset of an increase in secretion of androgens
What is puberty?
The stage of human development when sexual maturation and growth are completed. and result in an ability to reproduce
When are primary sexual characeristics established?
Before birth
When is the reproductive system inactive until?
Puberty
What is the onset age of puberty?
Variable
How does the age of puberty differ between boys and girls
Girls begin and end puberty before boys
Is the order of events in puberty consistent or variable?
Consistent, they happen in a recognised pattern
What does puberty consist of?
- Accelerated somatic growth
- Maturation of primary sexual characteristics
- Apperance of secondary sexual characteristics
- Menstruation and spermatogenesis behin
What does the accelerated growth phase in puberty follow?
The linear growth phase before puberty
What primary sexual characteristics develop in puberty?
Gonads and genitals
What secondary sexual characteristics appear at puberty?
- Pubic and axillary hair
- Female breast development
- Male voice changes
When does the menstruation and spermatogenesis begin?
At the end of puberty
What is puberty initated by?
The brain
What is the onset of puberty associated with?
Steady rise in FSH and LH secretion, due to a rise in GnRH secretion
Can the parts of the reproductive system work before the normal age of puberty?
Most can, but don’t because hormone levels are too low
In which sex does the growth spurt occur?
Both
How does the growth spurt differ between males and females?
Happens earlier, and results in shorter in females
Why are men taller?
Because the growth spurt is longer and slightly faster, and the linear phase is longer, so taller when start to spurt
What does the growth spurt depend on?
Growth hormones and steriods
How is the growth spurt ended?
In epiphyseal fusion
What closes epiphyseal growth plates in girls?
Oestrogen
What can be observed by the fusing of the growth plates?
The measureable end of puberty
How has the timing of puberty changed?
In Western countries, puberty is now much earlier.
The average age of menarche was 17 in 1800, now <13 years
What is the change in the age of onset of puberty due to?
Changes in nutrition and weight
What is the critical weight for the onset of puberty in females?
47kg
What is happening to the average age of body weight at onset of menarche?
It is staying the same
What happens in a female if there is significant weight loss?
The reproductive cycle ceases
In what situations may primary amenorrhea due to low body weight occur?
- Malnutrition
- Lean female athletes
In whom is the ‘body fat’ set point very noticable?
In girls with fluctating body weight due to anorexia nervosa
What may be involved in puberty signalling?
Leptins
What is true of many species, regarding puberty and menarche?
Breeding is seasonal, and so there is a new ‘puberty’ each year
What is the new puberty each year in some species triggered by?
Changes in day length
What gland is involved in the ‘new puberty’ in some species?
Pineal gland
What plays an important part in the pineal gland?
Secretion of melatonin
What evidence shows the involvement of the pineal gland in human puberty?
Pineal tumours can influence puberty in humans
What comes first in puberty, physical or hormonal changes?
Hormonal
What causes the hormonal changes in the onset of puberty?
Increased stimulation of the hypothalamo-pituitary-gonadal axis, and thus gradual activation of GnRH
What does the gradual activation of GnRH at the onset of puberty cause?
Increases frequency and amplitude of LH pulses
What happens in puberty once levels of gonadotrophins are high enough?
They stimulate the secretion of sexual steroids (oestrogens and androgens)
What extragonadal hormone changes occur at the onset of puberty?
Elevation of IGF-I and adrenal steroids
Draw a diagram illustrating the hormone changes that trigger the onset of puberty
Where is neuro-kinin B released from?
The arcuate area of the brain
What happens if there is destructive coding of Kiss 1 neuron arcuate?
Delayed onset of puberty
What happens is there is abnormal positive feedback on Kiss 1 neuron arcuate?
Early onset of puberty
What is the effect of GnRH secretion from the pituitary?
- Increases TSH
- Increases metabolic rate
- Promotes tissue growth
- Increases androgens
What is the result of the effect of GN secretion from the pituitary?
Results in growth spurt
What is the result of noctural GnRH pulsatility?
LH secretion precedes phenotypic changes by several years
What does the noctural GnRH pulsatility in pre-pubescent boys suggest?
Sleep related LH increase stimulates a noctural rise in testesterone
What could the noctural rise in testosterone in adolescent boys account for?
Some early pubertal changes seen in males
What pattern is seen similar to the noctural rise in testerosterone in pre-pubescent females?
Concomitant increase in oestrogen
What is true of LH and FSH levels in young children?
They are insufficient to initiate gonadal function
When do blood levels of LH and FSH increase?
Between 9-12 years
When to levels of LH and FSH increase until?
They reach levels high enough to initate gonadal development
What happens to the pulses of LH and FSH as a child gets older?
The amplitude of the pulses increases, especially during sleep
What are the first phenotypic changes in puberty?
- Breast development
- Testicular enlargement
What does an increase in LH and FSH lead to in males?
Spermatogenesis and androgen secretion
Other than the gonads, what else secretes androgen?
The adrenals
What does the secretion of androgens in males lead to?
- Sex accessory structures developments, e.g. prostate
- Male secondary sex characteristics, e.g. facial hair
- Growth of larynx, leading to the voice breaking
What induces secondary sex characteristics in females?
Oestrogen
What sexual secondary characteristics does oestrogen induce in females?
- Growth of pelvis
- Deposit of subcutaneous fat
- Maturation of internal reproductive organs and external genitalia
- Androgen release by adrenal gland increases
What does androgen release cause in females?
- Growth of pubic hair
- Growth of bone
- Increased secretion from sebaceous gland
How is pubertal development classified?
According to the Tanner standard
How many stages are there on the Tanner scale
5
What factors are staged on the Tanner scale in girls?
- Breast (B1-5)
- Pubic hair (Pu1-5)
- Axillary hair (A1-5)
- Menarche
What are the Tanner stages in girls?
What factors are staged in the Tanner standard in males?
- Testicular volume >4ml (Te)
- Penis enlargement (G1-5)
- Pubic hair (Pu1-5)
- Axillary hair (A1-5)
- Spermarche
What are the Tanner stages in boys?
What is the criteria for the pubertal growth acceleration?
Growth velocity is 2-3 times greater than prepubertal
At what age do girls start puberty?
9-13 years
What is the first physical sign of puberty in females?
B2 (breast development)
What is the growth velocity during puberty in females?
9.0cm/yr (Tanner II-III)
What is the duration of puberty in females?
2.4 years + - 1.1
At what age do boys start puberty?
10-14
What is the first sign of puberty in males?
G2 (testicular volume up to 4ml)
What is the growth velocity during puberty in males?
10.3 cm/yr
What is the duration of puberty in females?
3.2 yrs + - 1.8
What initates the first ovarian cycle?
LH surge
Is the LH surge usually sufficient to cause ovulation during the first cycle?
No, can take a couple of years to establish oogenesis
What happens once oogenesis is established?
It continues fairly regularly
What happens soon after the first ovarian cycle?
The brain and endocrine systems mature
What happens to oestrogen levels in the blood following the initiation of the first ovarian cycle?
They increase, due to the growing follicles
