Puberty

Male Development

 

Puberty begins with the appearance of secondary sexual characterstics and ends with the end of the growth spurt.

 

Normal male puberty occus between ages 9-14, 2 years after females.

 

 

Testicular volume enlargement is the first sign of puberty.

tanner 1:

tanner 2: testicular increase from 2- 4ml, sparse pubic hair

tanner 3: 8-10 ml - acceleration of puberty

tanner 4: penis length and breadth enlargement, coarse pubic hair, growth spurt

tanner 5: adult size and shape of penis, pubic hair to medial thigh

 

Gonadarche, or enlargement of the testes, is usually the first sign of pubery and often occurs at the same time as pubic hair growth. Spermatogenesis usually begins months after gonadarche.

 

The penis begins to grow about a year after gonadarche, is androgen-dependent, and continues after puberty.

Adrenarche leads to axillary and facial hair growth, body odour, and acne. The growth spurt in Tanner stage 4.

 

 

Delayed puberty:

• hypothalamic hypogonadism
  • functional: exercise, anorexia
  • genetic: Kallman's syndrome
  • anatomic: pituitary tumour
• hyperprolactinemia
• chronic illness
• primary hypogonadism

Female Development

 

Normal female puberty occurs between 8-13, though can begin as early as 6 in black girls.

 

Thelarche, onset of breast development, is the first stage. Asymmetry is common.

 

Adrenarche is the increase in adrenal androgens occurring before changes in the HPG axis, and is reponsible for growth of pubic and axillary hair, body odour, and acne.

 

Menarche occurs at a mean of 13 years, perhaps 2 years after breast development. It indicates the growth spurt is nearing completion.

• physiologic leukorrhea occurs 6 months prior to menarche, appearing as asymptomatic clear or milky vaginal discharge. It is due to endometrial stimulation by estrogen

Menstruation is often at first irregular, and it takes ~18 months for the first 12 periods.

 

 

Tanner stages

tanner 2: small breast bud; sparse labial hair

tanner 3: adult appearance, but smaller, hair over pubis

tanner 4: areola and nipple form secondary mound, coarse pubic hair

tanner 5: adult appearance, pubic hair extends to medial thigh

 

 

Pituitary Secretion

at puberty, the pituitary begins secreting pulses of gonadotrophins LH and FSH at night, with pulses occuring during the day in adults as well. Pulses are the same in both females and males, and play a key role in sexual differentiation.

 

anorexia inhibits these pulses and therefore puberty

• Gonadotrophins peak at 3 months - when mom's wash out, there is a feedback mechansism; low at 1-2 years
• Gonadarche begins with increased GnRH at sleep, leading to increases in FHS, then LH and estrogen
• it is really the LH levels that increase with puberty; GnRH and FSH remain similar throughout and so the ratio of LH/FSH increases and is a good indicator

breast development (thelarche) usually occurs first, but not always; menarche occurs, on average, two years after thelarche

• growth spurt (GH action, promoted by gonadal sex steriods) occurs over 2-4 years. Peak velocity is ~ 8.3 +/- 1.2 cm/year and occurs in Tanner 2-3
• final height = dad height + mom height /2 (+/- 5 cm) in M or F
• height inc 7.4 cm after menarche

 

• some evidence that puberty is occurring earlier; thelarche occurs at 9-10 y; menarche is ~12-13 years. also depends on race (black girls are earlier)
• menarche is well-predicted by family history. The Frisch hypothesis states that critical body weight (48 kg) and fat levels (17%) need to be met for menses to occur

 

Menarche is the beginning of the menstrual cycle.

It begins with hypothalamic secretion of GnRH, and other hormones, leading to adrenal androgen release and pituitary growth hormone.

GH causes the growth spurt a few years before menarche, and growth slows down as menarche begins. This is because increasing levels of estrogen, released by the ovaries, provides negative regulation of GH.

The hypothalamus begins secreting GnRH in episodic pulses of 2 hour intervals. This causes the release of FSH and LH.

Estrogen is the principle hormone secreted until age 8, though only in small quantities. After that, estrogen levels rise slowly and then more repidly after age 11. FSH plateaus at about age 13, while LH rises more slowly until a year before menarche. After that, a rapid rise occurs.

GnRH pulses ever 90 minutes, a pattern that contuines until age 40 and the beginning of menopause.

 

We believe the rise in LH is important in the onset of menarche, along with increased fat:lean body mass.

Menarche now occurs at age 12-13, earlier than age 15 a century ago. This is thought to be related to better childhood nutrition and fat stores, which mediate the transformation of androgen to estrogen. Rapidly rising estrogen levels lead to the LH surge.

Menarche can be delayed in people with poorer fat stores, such as athletes, people with anorxeia, or those in poorer health.