Normal Puberty

NORMAL PUBERTY

Timing of Puberty

• Definition: Puberty is a biologic transition in which secondary sex characteristics develop, a linear growth spurt occurs, fertility is realized, and psychosocial changes ensue.
• Adrenarche vs. Gonadarche:
  • Adrenarche: Maturation of adrenal androgens, usually earlier than gonadal maturation.
  • Gonadarche: Maturation of the hypothalamic–pituitary–gonadal (HPG) axis.
  • Thelarche: Pubertal breast development.
• Average Onset:
  • Girls (White): Mean onset ~10.6 years (range 7–13).
  • Girls (African American): Mean onset ~8.9 years (range 6–13).
  • Boys: Mean onset ~11 years (range 9–14); some African American boys start as early as 8–9 years.
• Determinants:
  • Body weight (adipose signals such as leptin) can influence puberty onset.
  • Multiple factors regulate hypothalamic GnRH pulse generator activation.

Hormonal Control

• HPG Axis:
  • Increased gonadotropins (LH, FSH) → gonadal (testis/ovary) secretion of sex steroids (androgens, estrogens).
• Adrenal Involvement:
  • Corticotropin (ACTH) + an unknown “adrenal androgen–stimulating factor” → adrenal reticular zone → adrenal androgens.
• Sex Steroids:
  • Androgens + Estrogens from gonads and adrenal glands → changes in hair growth, growth spurt, body composition, and epiphyseal maturation/fusion.

Growth Spurt and Body Composition

• Height Increase:
  • Pubertal growth spurt accounts for ~18% of final adult height.
  • Peak height velocity in girls ~8.3 cm/year at ~11.5 years; in boys ~9.5 cm/year at ~13.5 years.
  • Boys generally end up ~10 cm taller on average due to later onset & longer growth period.
• Hormones Involved:
  • Growth Hormone (GH), Insulin-like Growth Factor 1 (IGF-1), Estrogen (both sexes), and Testosterone (in boys).
  • Serum IGF-1 peaks during puberty and remains high ~2 years after peak growth velocity.
• U : L Ratio:
  • Ratio of upper to lower body segment. Decreases from ~1.7 at birth to ~1.0 by 10 years; ~0.92 in White adults, ~0.85 in African American adults.
  • Hypogonadism (delayed epiphyseal fusion) → prolonged limb growth → lower U : L ratio (eunuchoid habitus).
  • Excess estrogen → advanced bone age, short adult stature, higher U : L ratio.
• Bone Mass Changes:
  • 50% of total body calcium is laid down in bone during puberty. Boys generally end up with more skeletal mass; girls have wider hips.
• Body Composition:
  • Men have ~50% more lean body mass and skeletal mass; women have ~2× body fat (hips, upper arms, thighs, back).
  • Cardiovascular Changes: ↑aerobic reserve.

Tanner Stages (General)

• Developed by Marshall and Tanner: 5 stages describing external pubertal development.
• Girls: Breast (thelarche) + Pubic hair staging.
• Boys: Genital + Pubic hair staging.
• Stage 1: Prepubertal; Stage 5: Adult.

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FEMALE PUBERTY

Main Pubertal Events

1. Height Velocity Increase (often first sign).
2. Breast Development (Thelarche): Under ovarian estrogen control.
3. Pubic + Axillary Hair Growth: Under androgens from ovary + adrenal.
4. Menarche: Onset of menses (usually around Tanner stage 4).

Thelarche (Breast Development)

• Tanner Stage 1: Prepubertal (elevated papilla only).
• Stage 2: “Breast bud” with enlargement of areola diameter + small mound.
  • Mean onset of stage 2 ~10.3 years (White) vs. ~9.5 years (African American).
• Stage 3: Further enlargement of breast/areola, no contour separation.
• Stage 4: Areola + papilla project above breast, forming a secondary mound.
• Stage 5: Mature adult breast with areola recession, only papilla projects.

Pubic Hair Development

• Tanner Stage 1: Vellus-type hair, no difference from abdominal wall.
• Stage 2: Sparse, slightly pigmented, slightly curled hair along labia.
  • Mean onset of stage 2 ~10.4 years (White) vs. ~9.4 years (African American).
• Stage 3: Hair coarser, darker, curlier, sparsely over pubic region.
• Stage 4: Adult-type hair but covers a smaller area; not yet on medial thighs.
• Stage 5: Adult in quantity, type, distribution onto medial thighs.

Menarche and Ovarian Changes

• Menarche: Average onset ~12.8 years (White US), 6 months earlier in African American girls.
  • Usually 1–3 years after pubertal onset (Tanner stage 4).
  • Initial cycles may be anovulatory, irregular.
• Ovarian Maturation:
  • Follicles >4 mm develop, ovarian volume ↑ from <2 mL to ~2.8–15 mL.
• Other Changes:
  • Vaginal mucosa: Red, glistening → thicker, cornified epithelium.
  • Uterus grows from ~3 cm to 8 cm length.
  • Axillary hair ~12 years in ~90% African American girls vs. ~70% White girls.
  • Acne, caused by ovarian + adrenal androgens, can appear early.
  • Facial structural changes (nose, mandible, maxilla).

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MALE PUBERTY

Main Pubertal Events

1. Height Velocity Increase.
2. Genital Development (testicular enlargement, penile growth) – under LH/FSH stimulation → testosterone.
3. Pubic + Axillary Hair – from testicular + adrenal androgens.

• First sign typically testicular enlargement. This occurs ~6 months after breast budding onset in girls.
• Normal onset range for boys is 9–14 years.

Testicular Development

• Testicular Volume:
  • Prepubertal ~1–3 mL.
  • Puberty onset typically recognized at ~4 mL.
  • Adult ~29 mL average (slightly larger on right).
• Growth primarily from seminiferous tubules expansion.
• Leydig Cells: Appear under LH stimulation, produce testosterone.
• Spermatogenesis starts ~11–15 years.

Penile Growth

• Measuring: Flaccid + stretched length. ~6 cm prepubertal, ~12 cm in adult White men.
• Glans and overall length + width enlarge through Tanner stages.

Tanner Stages for Male Genitalia and Pubic Hair

1. Genital Stage 1: Childhood size penis, testes, scrotum.
   • Pubic Hair Stage 1: Vellus hair, no different from abdominal wall.
2. Genital Stage 2: Enlargement of testes/scrotum (reddening, texture change).
   • Pubic Hair Stage 2: Sparse, lightly pigmented hair at base of penis.
   • Average age ~11.2 for stage 2 genital changes.
3. Genital Stage 3: Penile length > width growth; further testis + scrotum enlargement.
   • Pubic Hair Stage 3: Darker, coarser, curlier hair spread sparsely.
4. Genital Stage 4: Increased penile length + width, development of glans; scrotum/testes enlarge further, scrotal skin darkens.
   • Pubic Hair Stage 4: Adult-type hair, smaller area, not on medial thighs.
5. Genital Stage 5: Adult size/shape of genitalia.
   • Pubic Hair Stage 5: Adult in quantity/type, spread to medial thighs.

Other Male Pubertal Changes

• Voice Deepening: Larynx + vocal cords enlarge between Tanner stages 3 and 4; adult voice by ~15 years.
• Facial Hair: Starts around corners of upper lip/cheek, eventually covering cheeks/chin after Tanner stage 5.
• Axillary Hair: Appears ~14 years.
• Acne: ~12 years onset (range 9–15), from adrenal + testicular androgens.
• Pubertal Gynecomastia: ~50% of boys, average age ~13, usually resolves in 1–2 years.
• Facial structural changes (nose, mandible, maxilla, sinuses) similar to females but often more pronounced.