Puberty Flashcards
What is puberty?
The transition phase that takes a person from being a sexually immature child to a sexually mature, reproductively fertile adult.
What is pubescence?
The state of the child between the onset of pubertal changes and the completion of sexual maturation.
What is the average age at which puberty begins in females?
12.75 years
What is the average age at which puberty begins in males?
14.75 years
What are ‘first signs’ of puberty?
Signs of puberty do not signify fertility, and do not even signify the beginning of puberty (which occurs some 2 years before these signs). They simply indicate that puberty is underway.
What are the first signs of puberty in females?
First menstruation (menarche)
What are the first signs of puberty in males?
First ejaculation
Why do the first signs of puberty not signify fertility?
- In females, the first menstrual cycle is anovulatory
- In males, the first ejaculation contains no spermatozoa
What is gonadarche and adrenarche?
Puberty is driven by hormones secreted from gonads (gonadarche) and adrenal glands (adrenarche)
What is the “growth spurt”?
Period of rapid growth during puberty
What are the properties of the growth spurt?
- Time of minimum growth velocity (‘take-off’): Time at which the growth spurt begins
- Time of peak height velocity: Time when maximum growing velocity is reached
- Time of decreased velocity and cessation of growth: Time when growth velocity reaches 0 and no more growth occurs (epiphyseal fusion)
What is the average year of “take off” in boys and girls?
- Boys: ~11 years
- Girls: ~9 years
What is the average height gain in boys and girls?
- Boys: ~28cm
- Girls: ~25cm
What is the explanation for average height difference between boys and girls (~10cm) after growth spurt?
The main reason for this height difference is that because the age of take-off is greater in boys, the height of boys at the age of take-off is also greater. Because the average height gain is about the same from growth spurt, boys tend to be taller than girls.
What are the differences in growth of different parts of the body between males and females?
- Shoulder growth is much greater in males compared to females, so men tend to have broader shoulders.
- Pelvic growth is much greater in females compared to males, so women tend to have broader hips.
What are the differences in changes in body composition in males compared to females?
- Adult males on average have 1.5x greater body mass compared to adult females.
- Adult females on average have 2x greater body fat content compared to adult females.
- Adult males on average have 1.5x greater skeletal mass compared to adult females.
- Adult males have greater muscle mass than adult females as a result of stimulation of muscle growth by androgens.
What are the reproductive changes that occur in females during puberty?
- In females, first ovulation occurs from a few months up to 2 years after menarche, accompanied by absence of periods for the few following months following menarche.
- There is maturation of the female genitalia (ovaries, oviducts, uterus and vagina).
What are the reproductive changes that occur in males during puberty?
- In males, there is maturation of the male genitalia (testes, vas deferens, seminal vesicles, prostate gland, scrotum and penis).
- Spontaneous erections also occur much more frequently, accompanied by nocturnal emissions (of seminal fluid).
What are the secondary sex characterstics in females?
- Growth and widening of the pelvis
- Pubic and axillary hair growth
- Breast growth
- Activation of sebaceous glands of the skin, leading to acne on face
- Slight deepening of voice
What are the secondary sex characterstics in males?
- Pubic and axillary (armpit) hair growth
- Facial and chest hair growth
- Activation of sebaceous glands of the skin, leading to acne on face
- Pigmentation of nipples
- Darkening and widening of areola
- Lengthening of vocal cords and deepening of voice (voice breaking)
What are the gonadal changes that occur in females?
Gradual decline in number of follicles from birth to puberty (500,000 → 83,000) as a result of atresia. However, the ovaries enlarge during puberty as a result of enlargement of the remaining follicles.
What are the gonadal changes that occur in males?
Spermatogenesis begins around 9 years of age, with production of mature spermatozoa at ~14-15 years of age. There is also enlargement of the testes (~24x) as a result of enlargement of the seminiferous tubules (due to filling with testicular fluid).
What is the condition characterised by the failure for testicular descent to occur and what are the consequences?
- Cryptorchidism
- Failure of spermatogenesis as it requires temperatures 3-4o below body temperature
What are the changes in gonadotrophin that occur during puberty?
- Pre-puberty: Levels of LH and FSH are low in blood, but fairly stable.
- Early-mid puberty: Levels of LH and FSH begin to rise (FSH rises first), with pulses becoming more prominent. Most of gonadotrophin pulsation occurs at night.
- Mid-late puberty: Gonadotrophin pulsations become greater during the day, but there is still substantially more release during the night.
- Adult: Stable pulsatile release throughout the whole of the day and night, with very little overall fluctuations.
What is the significance of changes in gonadotrophins during puberty and their relation to sex steroids?
Changes occur in absence of sex steroids, so are independent of feedback.
What is the first endocrine change that occurs during puberty?
In both males and females, the earliest detectable endocrine change is an increase in production of adrenal androgens, mainly DHEA (adrenarche).
What are the endocrine changes that occur in females during puberty?
- As the levels of gonadotrophins rise during puberty, levels of circulating oestrogens also rise (mainly oestradiol).
- This is a consequence of increased production by growing follicles under the stimulation of gonadotrophins.
- Oestrogens mediate development of many of the secondary sex characteristics.
- Androgen secretion from the adrenal glands also increase, mediating hair growth and may also cause behavioural changes such as increase sex drive.
How does menarche occur?
- At menarche, there is a surge in gonadotrophins (mainly LH) that drives menstruation, but not ovulation.
- As the hormone axis matures, the LH surge becomes capable of causing ovulation.
What are the endocrine changes that occur during puberty in males?
- As the levels of gonadotrophins rise, androgen secretion from the testes also rise, in synchrony with the pulsatile release of gonadotrophins.
- Androgens mediate development of all male secondary sexual characteristics.
What are the causes of acne?
- Testosterone causes increased secretions from skin sebaceous glands.
- Glands become clogged and infected.
What are the functions of growth hormone during puberty?
- Stimulates growth of long bones and tissues
- Mediates metabolic changes that promote growth (e.g. increased gluconeogenesis, protein synthesis…)
What are the functions of thyroid hormone during puberty?
- Aids in growth
- Increases metabolic rate
What is the overall seqence of endocrine events that occur during puberty?
↑ Pulsatile release of GnRH
↓
↑ Pulsatile release of gonadotrophins
↓
↑ Synthesis of sex hormones
↓
Development of secondary sex characteristics
What is the peripheral suppression hypothesis for initiation of puberty?
- Hypothalamus very sensitive to feedback inhibition of GnRH secretion by sex hormones during childhood.
- Low levels of circulating sex steroids in circulation inhibit onset of puberty.
- As puberty approaches, central mechanisms cause decreased sensitivity of hypothalamus to sex steroids, leading to increased secretion of GnRH and thus onset of puberty.
What evidence is there for the peripheral suppression hypothesis?
Smaller amounts of oestrogens are needed to inhibit secretion of gonadotrophins in pre-pubescent girls than adult women.
What is the central suppression hypothesis for initiation of puberty?
- GnRH secretion is actively inhibited by other areas of the brain during childhood.
- Central changes at puberty result in the release of inhibition and increased GnRH secretion.
What evidence is there for the central suppression hypothesis?
Lesions in specific areas of rat brains cause early onset of puberty.
What changes may occur that allow positive feedback effect of oestrogens on gonadotrophin to occur following puberty?
- Maturation of hypothalamic centres responsible for positive feedback (i.e. anterior hypothalamus)
- Ability for gonadotrophs to synthesise and store enough gonadotrophins for adequate amount to be released during surge
What neuropeptides may be involved in initiating puberty?
- Kisspeptin
- Neurokinin B
What factors can influence puberty?
- Nutrition
- Day-night cycle
- Stress
- Pollutants
- Climate
- Genetics
How can nutrition influcence onset of puberty?
- Puberty may occur at a set body weight
- This may be mediated by leptin
How can stress influence onset of puberty?
- Stress seems to accelerate puberty (may be mediated by cortisol)
How can altitude influence onset of puberty?
Increase in altitude by 100m causes delay in puberty by 3 months.
