7. Puberty

Question 1

What is puberty?

Answer 1

Developmental stage during which adolescents reach sexual maturity and become capable of reproduction
Involves:
-Growth in stature
-Change in body composition
-Development of secondary sexual characteristics
-Achievement of fertility

Question 2

Difference between primary and secondary sexual characteristics?

Answer 2

Primary: Reproductive organs, present at birth
Secondary: Develop during puberty, not directly part of reproductive system

Question 3

What is adrenache?

Answer 3

Maturational increase in adrenal androgen (DHEA-S) production
In the Hypothalamic-pituitary-adrenal axis
Around age 6 in boys and girls
Occurs in conjunction with gonadal maturation
Leads to:
1. Development of pubic and axillary hair (pubarche)
2. Development of pilosebaceous unit in the skin-acne
3. Increase cortical bone density

Question 4

What is the primary stimulus for adrenarche?

Answer 4

Enhanced adrenal sensitivity to ACTH (adrenocorticothoric hormone)

Question 5

Events of puberty in females?

Answer 5

1. Breast development (Thelarche)
   - First sign
   - Usually between 8.5 and 12.5 years
2. Pubic hair growth (pubarche) and rapid height spurt
   - Occur almost immediately after breast development
3. Menarche
   - Average age 13yrs
   - Signals end of growth (5cm height gain remaining)

Question 6

What is the tipping point to the beginning of menarche?

Answer 6

As ovaries matures, the become more sensitive to gonadotropin and release more steroid hormones.
When these levels become high enough to exert negative feedback on gonadotropin secretion, a cycle will develop and menarche can occur

Can take up to 18months for regular ovulatory cycles to develop

Question 7

What is the HPO axis?

Answer 7

Hypothalamus pituitary ovarian (HPO) axis

Question 8

Signs of male puberty

Answer 8

1. Testicular enlargement to greater than 4mls volume
   - First sign
   - At 10-15yrs
2. Pubic hair growth and penile growth
   - Normally 2 years interval between onset of pubic hair and axillary and facial hair
3. Spermarche: The appearance of sperm in seminal fluid
   - Mean age 13.4yrs
4. Growth spurt
   - When testicular volume is 12-15mls, after 18month delay
   - Growth spurt in males later and of greater magnitude

Question 9

What is the HPG axis?

Answer 9

Hypothalamic-pituitary-gonadal axis
Leads to:
- FSH/LH promotes testes to produces testosterone
- FSH promotes testicular enlargement
- Testosterone promotes penile enlargement
- Testosterone critical for spermatogenesis

Question 10

Androgen-dependent secondary sexual characteristics?

Answer 10

Dependent on testosterone and it’s metabolite DHT (Dihydrotestosterone)
• Facial, underarm, pubic hair
• Deepening of voice (due to growth of larynx)
• Thick secretion of skin oil glands (can cause acne)
• Masculine pattern of fat distribution
• Bone growth via growth hormone secretion. Then termination via closure of epiphyseal plates
• Stimulation of muscle protein synthesis
• Erythropoietin stimulation giving higher haematocrit in males

Question 11

How is puberty initiated?

Answer 11

Gonadotrophin (LH/FSH) release

• Suppressed by continuous infection of GnRH
• Pulsatile administration will lead to gonadal stimulation, maturation and production of steroid hormones

Question 12

4 phases of human growth

Answer 12

1. Fetal – uterine environment, fastest, 30% of eventual height determined
2. Infantile – nutrition, general health, happiness and thyroid function, (birth -18months) rapid but decreasing growth rate, 15%
3. Childhood – dependent on thyroid hormones, growth hormone, general health and happiness, genetics. Slow steady prolonged.
4. Pubertal – sex hormones esp testosterone and oestrogen, growth hormone and insulin-like growth factor

Question 13

Why are boys taller?

Answer 13

Later onset of growth spurt in boys (about 2 years) accounts for overall greater final height as they achieve more growth before peak velocity

Question 14

Why does puberty limit height?

Answer 14

Puberty limits adults height as gonadal steroids lead to epiphyseal closure of long bones

Question 15

Difference in male and female body compositition?

Answer 15

In adults
• Males gain greater amounts of fat-free mass and skeletal mass
• Females acquire significantly more fat mass

Question 16

Factors contributing to earlier puberty?

Answer 16

Genetics – Fhx of early puberty. Timing correlates with mother and sisters.

Social factors
• Lower social class = higher rate of obesity = earlier menarche

Geographic factors – closer to equator, lower altitudes, urban setting

Environmental exposures – endocrine disrupting chemicals, industry uses e.g. plastics, agriculture, fuels

Race – onset earlier in Afro-Carribean and African-American children compared to white children

Question 17

Why would increase in body fat may play a critical role in the turning on of adrenal androgen secretion and adrenarche?

Answer 17

Leptin may be link between adipose tissue, energy homeostasis centres in hypothalamus and the reproductive system

Question 18

What are the stages of ovarian failure once a women reaches 40yrs?

Answer 18

1. Cycles become irregular as women reach the climacteric age 40 (10 years of change that leads to menopause)
2. Between 45 – 55 years (average 51.5 for the past 100 years)
3. Follicle supply diminishes (but doesn’t ‘run out’)
4. Follicle cells gradually become insensitive to FSH and LH
5. Ovarian steroid levels fall
6. No negative feedback to the pituitary therefore dramatic increase in levels of FSH and LH. Low oestrogen levels produced by adrenals

Question 19

Menopause symptoms?

Answer 19

• Vascular instability: I.e. Night sweats and hot flushes
• Atrophy of all oestrogen dependant tissues:
-Breast, uterus, vagina, bladder, urethra (atrophic vaginitis)
- Skin collagen loss
- Bone catabolism with loss of Ca++ leads to osteoporosis
- LDL rises - increasing the risk of coronary thrombosis
• Rise in adrenal androgens may lead to hirsuitism
• Loss of libido
• Depression, anxiety, mental confusion

Question 20

Treatment for menopause

Answer 20

HRT

Replaces steroids, maintains oestrogen dependent tissues and delays oesteoporosis

Question 21

In total, thelarche, growth spurt, pubarche and menarche require…

Answer 21

about 4.5 years (range 1-6)

Question 22

Peak velocity of growth?

Answer 22

Peak velocity
• Girls mean age 11.5
• Boys mean age 13.5

Question 23

Biochemistry of menopause?

Answer 23

Ne negative feedback to the pituitary therefore dramatic increase in FSH and LH levels. FSH excreted in urine as levels are so high
Low levels of sex steroids are produced by the adrenals