Puberty

Question 1

What is puberty?

Answer 1

The transition phase that takes a person from being a sexually immature child to a sexually mature, reproductively fertile adult.

Question 2

What is pubescence?

Answer 2

The state of the child between the onset of pubertal changes and the completion of sexual maturation.

Question 3

What is the average age at which puberty begins in females?

Answer 3

12.75 years

Question 4

What is the average age at which puberty begins in males?

Answer 4

14.75 years

Question 5

What are ‘first signs’ of puberty?

Answer 5

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.

Question 6

What are the first signs of puberty in females?

Answer 6

First menstruation (menarche)

Question 7

What are the first signs of puberty in males?

Answer 7

First ejaculation

Question 8

Why do the first signs of puberty not signify fertility?

Answer 8

• In females, the first menstrual cycle is anovulatory
• In males, the first ejaculation contains no spermatozoa

Question 9

What is gonadarche and adrenarche?

Answer 9

Puberty is driven by hormones secreted from gonads (gonadarche) and adrenal glands (adrenarche)

Question 10

What is the “growth spurt”?

Answer 10

Period of rapid growth during puberty

Question 11

What are the properties of the growth spurt?

Answer 11

1. Time of minimum growth velocity (‘take-off’): Time at which the growth spurt begins
2. Time of peak height velocity: Time when maximum growing velocity is reached
3. Time of decreased velocity and cessation of growth: Time when growth velocity reaches 0 and no more growth occurs (epiphyseal fusion)

Question 12

What is the average year of “take off” in boys and girls?

Answer 12

• Boys: ~11 years
• Girls: ~9 years

Question 13

What is the average height gain in boys and girls?

Answer 13

• Boys: ~28cm
• Girls: ~25cm

Question 14

What is the explanation for average height difference between boys and girls (~10cm) after growth spurt?

Answer 14

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.

Question 15

What are the differences in growth of different parts of the body between males and females?

Answer 15

• 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.

Question 16

What are the differences in changes in body composition in males compared to females?

Answer 16

• 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.

Question 17

What are the reproductive changes that occur in females during puberty?

Answer 17

1. 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.
2. There is maturation of the female genitalia (ovaries, oviducts, uterus and vagina).

Question 18

What are the reproductive changes that occur in males during puberty?

Answer 18

1. In males, there is maturation of the male genitalia (testes, vas deferens, seminal vesicles, prostate gland, scrotum and penis).
2. Spontaneous erections also occur much more frequently, accompanied by nocturnal emissions (of seminal fluid).

Question 19

What are the secondary sex characterstics in females?

Answer 19

1. Growth and widening of the pelvis
2. Pubic and axillary hair growth
3. Breast growth
4. Activation of sebaceous glands of the skin, leading to acne on face
5. Slight deepening of voice

Question 20

What are the secondary sex characterstics in males?

Answer 20

1. Pubic and axillary (armpit) hair growth
2. Facial and chest hair growth
3. Activation of sebaceous glands of the skin, leading to acne on face
4. Pigmentation of nipples
5. Darkening and widening of areola
6. Lengthening of vocal cords and deepening of voice (voice breaking)

Question 21

What are the gonadal changes that occur in females?

Answer 21

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.

Question 22

What are the gonadal changes that occur in males?

Answer 22

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).

Question 23

What is the condition characterised by the failure for testicular descent to occur and what are the consequences?

Answer 23

• Cryptorchidism
• Failure of spermatogenesis as it requires temperatures 3-4^o below body temperature

Question 24

What are the changes in gonadotrophin that occur during puberty?

Answer 24

1. Pre-puberty: Levels of LH and FSH are low in blood, but fairly stable.
2. 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.
3. Mid-late puberty: Gonadotrophin pulsations become greater during the day, but there is still substantially more release during the night.
4. Adult: Stable pulsatile release throughout the whole of the day and night, with very little overall fluctuations.

Question 25

What is the significance of changes in gonadotrophins during puberty and their relation to sex steroids?

Answer 25

Changes occur in absence of sex steroids, so are independent of feedback.

Question 26

What is the first endocrine change that occurs during puberty?

Answer 26

In both males and females, the earliest detectable endocrine change is an increase in production of adrenal androgens, mainly DHEA (adrenarche).

Question 27

What are the endocrine changes that occur in females during puberty?

Answer 27

- 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.

Question 28

How does menarche occur?

Answer 28

- 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.

Question 29

What are the endocrine changes that occur during puberty in males?

Answer 29

- 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.

Question 30

What are the causes of acne?

Answer 30

- Testosterone causes increased secretions from skin sebaceous glands. - Glands become clogged and infected.

Question 31

What are the functions of growth hormone during puberty?

Answer 31

1. Stimulates growth of long bones and tissues 2. Mediates metabolic changes that promote growth (e.g. increased gluconeogenesis, protein synthesis…)

Question 32

What are the functions of thyroid hormone during puberty?

Answer 32

1. Aids in growth 2. Increases metabolic rate

Question 33

What is the overall seqence of endocrine events that occur during puberty?

Answer 33

↑ Pulsatile release of GnRH ↓ ↑ Pulsatile release of gonadotrophins ↓ ↑ Synthesis of sex hormones ↓ Development of secondary sex characteristics

Question 34

What is the peripheral suppression hypothesis for initiation of puberty?

Answer 34

1. Hypothalamus very sensitive to feedback inhibition of GnRH secretion by sex hormones during childhood. 2. Low levels of circulating sex steroids in circulation inhibit onset of puberty. 3. As puberty approaches, central mechanisms cause decreased sensitivity of hypothalamus to sex steroids, leading to increased secretion of GnRH and thus onset of puberty.

Question 35

What evidence is there for the peripheral suppression hypothesis?

Answer 35

Smaller amounts of oestrogens are needed to inhibit secretion of gonadotrophins in pre-pubescent girls than adult women.

Question 36

What is the central suppression hypothesis for initiation of puberty?

Answer 36

1. GnRH secretion is actively inhibited by other areas of the brain during childhood. 2. Central changes at puberty result in the release of inhibition and increased GnRH secretion.

Question 37

What evidence is there for the central suppression hypothesis?

Answer 37

Lesions in specific areas of rat brains cause early onset of puberty.

Question 38

What changes may occur that allow positive feedback effect of oestrogens on gonadotrophin to occur following puberty?

Answer 38

1. Maturation of hypothalamic centres responsible for positive feedback (i.e. anterior hypothalamus) 2. Ability for gonadotrophs to synthesise and store enough gonadotrophins for adequate amount to be released during surge

Question 39

What neuropeptides may be involved in initiating puberty?

Answer 39

1. Kisspeptin 2. Neurokinin B

Question 40

What factors can influence puberty?

Answer 40

1. Nutrition 2. Day-night cycle 3. Stress 4. Pollutants 5. Climate 6. Genetics

Question 41

How can nutrition influcence onset of puberty?

Answer 41

- Puberty may occur at a set body weight - This may be mediated by leptin

Question 42

How can stress influence onset of puberty?

Answer 42

- Stress seems to accelerate puberty (may be mediated by cortisol)

Question 43

How can altitude influence onset of puberty?

Answer 43

Increase in altitude by 100m causes delay in puberty by 3 months.