Lecture 20: Puberty Flashcards
What is puberty?
Puberty is a physical, emotional and sexual transition from childhood to adulthood
What do hormonal changes at puberty lead to;
Behavioural responses;
- Increases in libido
- Erotic fantasies
- Sexual behaviour
Physical changes
- Growth of genitals
- Appearance of secondary sexual characteristics
What does peter gluckman think about puberty today?
Nowadays people are undergoing sexual development earlier, within an increasing social milieu but slow rate of neural maturation
i.e becoming physically like an adult earlier but mentally not there.
Describe hormone levels during development;
During fetal and perinatal development there are surges in hormones which settle down soon after birth, then spike again for puberty in a cyclic manner in women. Certain hormones rise after menopause too
Why do gonadotrophin levels change from birth onwards;
- Establishment of negative feedback mechanisms
2. Loss of placental hormones
what are the mechanisms for keeping reproduction function on hold?
Largely unknown
Puberty is the re-awakening of the reproductive endocrine system.
What is adrenarche;
Adrenal maturation b/c of androgens
What is pubarche
Appearance of pubic hair b/c of androgens
What is thelarche
Breast development b/c oestrogen
What is menarche
first mensturation b/c oestrogen
What is spermarche
Onset of spermatogenesis b/c androgens
Describe the tenner stages of development of girls
Stage One ; Breast development
Stage two ; Sexual hair development
Stage Three; Growth spurt
Stage four ; Menarche
Describe the first stage of secondary development in girls
Breast development
Age; 10-11
- With the beginning of oestradiol secretion by the ovarian follicles the breast bud rises on the chest wall
- The nipples and areola enlarge and elevate, followed by formation of the breast mound
- Ovulation with subsequent progesterone secretion, leads to full breast development
Describe the development of sexual hair
age 10-12 usually within 6 months of breast bud appearance
- Due to exposure of hair follicles on the mons pubis and labia majora to androgens
- Axillary hair follows 1 year after pubes
- apocrine glands of the mons pubis and axillae enlarge and begin excreting volatile organic acids.
Does breast development occur first always?
Breast development usually occurs first but in ~15% of girls pubic hair develops first. A delay of 6 months suggest androgen excess
Describe the growth spurt in secondary sexual development
After breast development, testicular development (Boys), see increased growth acceleration.
Growth is both stimulated by steroid hormones with epiphyseal closure by oestrogen.
Girls; 11-12 and boys; 13-15
full height ; girls =17 and boys = 21
What can bone development be a useful indicator for?
Bone change correlates with secondary sexual characteristics better than chronological age, important for assessment of precocious development.
Describe menarche;
Average age; 12-13 years
95% between 11-15
However, if first ovulation does not take place until 6-9 months after menarche, because the positive feedback mechanisms of estrogen have not developed.
Regulatory ovulatory cycles begin 1-2 years after menarche.
Describe the tenner stages of male development;
1) Testicular growth (12)
2) Sexual hair growth (12-13)
3) Penile Growth (13)
4) Peak Growth spurt (14)
5) Spermarche (14+)
Describe how testicular and penile enlargement occur;
Gonadotrophin secretion causes leydig cells to enlarge and secrete testosterone affecting the seminiferous tubules, giving rise to increased testicular size
Elongation and enlargement of the penis occurs within a year of testicular enlargement
Describe sexual hair growth in boys;
Pubic hair appears around 6 months after the beginning of testicular enlargement
Axillary hair begins 18 months later, and facial hair later
Describe spermarche
Motile sperm is first seen in the urine at 13-14 years
First conscious ejaculation occurs soon after 14+
Describe how physical changes occurs in boys and girls
Body shape in boys and girls is determined by the differential affects of estrogen and androgen
Males are more muscular, taller and aggressive.
Females show fat distribution to buttocks and breasts. Growth and widening of the bony pelvis to provide a larger birth canal.
Describe the endocrine changes during puberty;
The increase in plasma LH levels is the first neuroendocrine signs of puberty, and is the result of an increase in GnRH release (increased frequency, amplitude and baseline)
When does gonadotrophin release occur during puberty?
Gonadotrophin secretion (LH and FSH) occurs in early puberty at night during sleep.
In early puberty there is increase magnitude, frequency of LH and FSH, reflecting sleep augmented release.
In late puberty, daytime LH pulses increases also
Describe the endocrine changes in boys during puberty;
Testosterone levels in plasma follow the gonadotrophins
Thus, Testosterone rises at night (with LH) in early puberty, and is seen to rise during the day in later puberty
Describe endocrine changes in girls during puberty;
- Oestradiol levels raise consistently through puberty until it reaches the Conc. seen in mature women
- Responsible for secondary sexual characteristics
Oestrogen levels are lower in boys
Describe adrenarche;
- The earliest endocrine change is progressive increase in the concentrations of adrenal androgens; DHEA, DHEAS and androstenedione.
Describe how adrenarche is selective;
Adrenal maturation is selective, in that glucocorticoids and mineralcorticoids secretion does not increase at the same time
When does adrenarche occur?
It starts around years and occurs until 13-15
What is the function of these developed adrenal glands?
No clear function but these adrenal androgens appear to promote pubic and axillary hair growth
What are the two mechanisms suggested to cause puberty?
1) The gonadostat hypothesis
2) Hypothalamic maturation
Describe gonadostat hypothesis;
Similar patterns of gonadotrophin secretions are seen in both normal agonodal humans
Therefore; hypothalamic maturation
Describe the hypothalamic maturation hypothesis
Suggests that puberty is driven by a primary change in the hypothalamic output of GnRH
What is the current explanation on the timing of puberty onset;
Puberty onset is suppressed by;
- Feedback inhibition of the HPA axis
- Suppression of GnRH release by central neural pathways
What is normal puberty onset the result from;
- Increased stimulation of GnRH neurons
- Decreased inhibition of GnRH neurons
- Increased production of Glial growth factors
Leptin appears to trigger this pulsatile GnRH
What has been noticed in general about puberty onset?
That over the last decade it is occurring earlier
What has been observed regarding weight and puberty onset;
- In girls a critical weight must be achieved to active the HPA axis so the growth spurt can occur
- ~30kg for growth spurt
- ~47kg for menarche
i.e Body weight, critical metabolic weight, fat;lean mass ratio may influence hypothalamic feedback
What has been observed regarding females and fathers, regarding the onset of puberty?
Girls with step fathers reach puberty faster (9 months earlier)
Called the vandenbergh affect in mice
What defines precocious puberty;
The appearnce of physical and hormonal signs of puberty before;
7 years in white girls
6 years in african american girls
9 years in boys
What are the types of precocious puberty?
GnRH dependant (a.k.a central or true) precocious puberty
GnRH independant precocious puberty (aka peripheral or pseudo)
Write some short notes on GnRH dependant precocious puberty;
- Early activation of pulsitile GnRH secretion
- Most common
- May be idiopathic, CNS lesion, injury, congenital anomalies, genetic
Write some short notes on GnRH independant precocious puberty;
Occurs when the gonads operate independantly of the HPA
- i.e b/c premature sex steroid secretion
- Secondary to ovarian cysts, tumours, testicular tumours, or syndromes
What are the problems associated with precocious puberty?
Children left untreated do not reach full adult height potential b/c premature epiphyseal closure)
- Boys 1.6m<
- Girls 1.5m<
- Emotional distress
What is the treatment of central percocious puberty?
- GnRH agonists
- temporarily stops puberty
- preserve adult height potential
Describe treatment for pseudo percocious puberty;
- Individualised
- Based on underlying disorder
What is the frequency of GnRH dependant puberty?
Rare disorder
Affects 1/5000 to 1/10000 children
Female gender preference 23:1 boys
Some girls diagnosed may just be normal
Describe delayed puberty symptoms;
The lack of physical and hormonal signs of puberty
- 13 years in girls
- 14 years in boys
Why does delayed puberty occur?
Occurs when the gonadotrophins signals from the pituitary are inadequate to produce follicular maturation and subsequent sex steroid hormone secretion
What can cause delayed puberty?
- Kallman syndrome
- Neurological tumors
- Low body weight, exercise induced amenorrhea, stress induced amenorrhea
