Puberty
last authored: April 2012, David LaPierre
last reviewed:
Puberty begins with the appearance of secondary sexual characterstics and ends with the end of the growth spurt.
Puberty occurs following maturation of the HPG axis. Increased pulsatile release of GnRH leads to release of LH and FSH, causing gonadal maturation and release of sex steroids. Adrenal production of androgens also occurs.
- male development
- female development
Male Development
Normal male puberty occus between ages 9-14, 2 years after females.
Testicular volume enlargement is the first sign of puberty, and represents gonadarche. Spermatogenesis usually begins in the months that follow. The penis begins to grow about a year after gonadarche, is androgen-dependent, and continues after puberty.
Adrenarche involves the development of axillary and facial hair, as well as body odour and acne.
The growth spurt occurs during in Tanner stage 4.
tanner 1: no growth
tanner 2: testicular increase from 2- 4ml, sparse pubic hair
tanner 3: testicular increase to 8-10 ml - hair grown continues over pubis
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
Female Development
Normal female puberty occurs between 7-13, though can begin as early as 6 in black girls.
Thelarche, onset of breast development, is the first stage. Asymmetry of breast growth is common.
Adrenarche usually follows next, involves the growth of pubic and axillary hair, body odour, and acne. It is mediated by an increase in adrenal androgens occurring before changes in the HPG axis.
The growth spurt occurs next.
Menarche, or onset of menstruation, begins 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. It often takes 18 months for the first 12 periods to occur.
Tanner stages
tanner 1: no growth
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
Endocrine Biology
Pituitary Secretion
At puberty, the hypothalamus begins secreting GnRH pulses every 90-120 minutes, a pattern that contuines until age 40 and the beginning of menopause. 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.
Gonadarche begins with increased GnRH at sleep, leading to increases in FSH, 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. Many people believe that LH is important in the onset of menarche.
Menarche, the beginning of the menstrual cycle, 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 now a few years earlier than in girls 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.
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.
Estrogen is the principle hormone secreted until age 8 or so, though only in small quantities. At this point, estrogen levels rise slowly and then more rapidly. FSH plateaus at about age 13, while LH rises more slowly until a year before menarche. After that, a rapid rise occurs.
Normal Pubertal Variations
Premature Andrearche
Can occur in boys and girls before age six, leading to pubic and axillary hair, body odour, and mild acne. Caused by adrenal production of DHEAS. Investigate for other signs of puberty (thelarche in girls or testicular enlargement in boys). Exclude androgen-secreting tumours.
Gynecomastia
Common; seen in 50% of male adolescents.
Transient, can be asymptomatic
Investigate if nipple discharge or fixed mass.
Distingusih breast tissue from fat
Delayed Puberty
Delayed puberty, or the absence of puberty by age 13 in girls and 14 in boys, is common in males but rare in females. It affects ~3% of females and is more worrying.
- boys
- girls
Boys
Delayed puberty is often normal in boys, but also has a number of pathologic causes:
hypothalamic hypogonadism
- functional: exercise, anorexia
- genetic: Kallman's syndrome
- anatomic: pituitary tumour
hyperprolactinemia
chronic illness
primary hypogonadism
Girls
Delayed puberty is defined as:
- a lack of pubertal development at 2 sd for general population in geographical area
- no breast devt by age 14
- no menses by age 16 or menses 4 years after thelarche: primary amenorrhea
- secondary amenorrhea: over 6 months with no menses
Potential causes:
hypothalamus-pituitary
|
genetic
|
gonads
other
|
Investigations
history: weight loss, growth, family history, illness
physical exam: growth curve, Tanner staging, neurological exam
labs: estradiol, testosterone, LH, FSH, TSH, GnRH
imaging: bone age, CT, MRI of head, adrenal ultrasound and pelvis
karyotype to rule out Turner syndrome
Treatment
Treat the underlying cause
Replace cyclic estradiol and progesterone for females and testosterone for males
 |