Puberty

Puberty is a complex series of physical, psychosocial, and cognitive transitions usually experienced by adolescents (11–19 years of age). Puberty is marked by a growth in stature and the development of secondary sexual characteristics, achievement of fertility, and changes in most body systems. Being familiar with normal puberty is important to be able to recognize and manage abnormalities such as precocious puberty or delayed puberty.

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Overview

Definition

Puberty is the time period from the 1st appearance of secondary sexual characteristics until achieving complete sexual development. Puberty involves a complex series of physical, psychosocial, and cognitive changes.

Onset

  • Median age of the onset of puberty has decreased in recent years.
  • Range:
    • 8–13 years in girls 
    • 8–12 years in boys

Hormonal control in the initiation of puberty

  • A critical event in puberty is an increase in the pulsatile secretion of gonadotropin-releasing hormone (GnRH) from the arcuate nucleus in the hypothalamus.
    • Kisseptin neurons in the arcuate nucleus release neurokinin B and dynorphin.
    • Neurokinin B and dynorphin cause the pulsatile secretion of GnRH.
  • GnRH causes the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary gland. Both LH and FSH affect the Leydig and Sertoli cells in the testes and the theca and granulosa cells of the ovary.
  • Zona reticularis of the adrenal glands secretes androgens such as DHEA, resulting in the characteristics of adrenarche. Zona reticularis functions separately from the hypothalamic-pituitary-gonadal axis.
  • Hormonal changes in girls:
    • LH acts on the theca cells of the ovary to convert cholesterol into androgens.
    • Granulosa cell converts the androgens to estradiol under the control of FSH signaling. 
    • Estradiol acts on various organs until the completion of puberty.
  • Hormonal changes in boys:
    • LH acts on Leydig cells to convert cholesterol into testosterone.
Development of the normal hypothalamic–pituitary–gonadal (HPG) axis in females

Normal hypothalamic–pituitary–gonadal (HPG) axis in females

GnRH: gonadotropin-releasing hormone
FSH: follicle-stimulating hormone
LH: leutinizing hormone
Image by Lecturio. License: CC BY-NC-SA 4.0

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Physical Changes During Puberty

Puberty can be divided into 4 different consecutive stages, namely, thelarche, pubarche, growth spurt, and menarche.

Thelarche

  • Breast development with formation of the breast bud and proliferation of the duct and gland epithelium
  • 1st sign of puberty in girls
  • Participating hormones: estrogen, estradiol, prolactin
  • Onset: 7–14 years of age

Pubarche

  • Growth of pubic and armpit hair
  • Participating hormones: testosterone, 5α-dihydrotestosterone
  • Onset: 8–15 years of age

Growth spurt

  • Onset:
    • On average, 2 years earlier in girls than boys 
    • Approximately 1 year after the 1st indicators of puberty
  • 3–10 cm of growth per year
  • Participating hormones:
    • Release of sex steroids leads to the production of growth hormones.
    • Leads to production of insulin-like growth factor-1 in the liver

Menarche

  • 1st menstrual bleeding
  • Due to estrogen withdrawal without preceding ovulation
  • Onset:
    • Between 9 and 16 years of age
    • Approximately 1 year after a growth spurt
  • Normally occurs later than other signs of puberty.

Tanner Stages of Development

“Tanner staging” is a scale that measures the physical/sexual development in children and adolescents. This staging technique involves the evaluation of genitalia in males, breast in females, and pubic hair in both.

Table: Tanner stages in females
Tanner 1Tanner 2Tanner 3Tanner 4Tanner 5
AgePrepubertal8–11.5 years11.5–13 years12–15 years> 15 years
Pubic hairVillus hair onlySparse hair along the labiaCoarse and curly hair covers the pubis.Adult hair that does not spread to the thighAdult hair reaching the thigh
BreastsElevation of papilla onlyBreast buds are palpable (1st sign of puberty in females) and areolae are enlarged.Breast tissue grows with no contour or separation.Breasts enlarge and areolae form secondary mound on the breast.Adult breast contours are present. Only the papilla is raised.
Other observationsAdrenarche and ovarian growthClitoral enlargement, labial pigmentation, growth of uterusAxillary hair, acneMenarche and development of mensesAdult genitalia
Table: Tanner stages in males
Tanner 1Tanner 2Tanner 3Tanner 4Tanner 5
AgePrepubertal8–11.5 years11.5–13 years12–15 years> 15 years
Pubic hairVillus hair onlySparse hair at base of the penisCoarse and curly hair appears over the pubis.Adult-quality hair in the pubic area, sparing the thighAdult-quality hair in the pubic area, reaching the thigh
Genitalia
  • Testes < 2 cm
  • No growth of the penis
  • Testes: 2.5–3.2 cm
  • Thinning and reddening of the scrotum
  • Testes: 3.3–4 cm
  • Increase in length of the penis
  • Testes: 4.1–4.5 cm
  • Growth of the penis, darkening of the scrotum
  • Testes > 4.5 cm
  • Adult genital size
Other observationsAdrenarcheDecrease in body fatGynecomastia, breaking of voice, increased muscle massAxillary hair, voice change, acneFacial hair, increase in muscle mass

Clinical Relevance

  • Iron deficiency anemia: a condition affecting adolescent girls due to menstrual bleeding and insufficient iron intake. Males are less prone to anemia because testosterone increases erythropoiesis.
  • Gynecomastia: enlargement or swelling of the breast tissue in men. Gynecomastia affects approximately 50% of teenage boys at an average age of 13 years. Gynecomastia is caused by the increased production or action of estrogens, enhanced breast-tissue sensitivity to estrogens, or the decreased production or action of androgens.
  • Acne vulgaris: a disorder of the pilosebaceous unit due to follicular hyperkeratinization, excess sebum production, follicular colonization by Cutibacterium acnes, and inflammation. Severity of acne is associated with high serum levels of dehydroepiandrosterone sulfate.
  • Dysfunctional uterine bleeding: excessive, prolonged, and/or irregular endometrial bleeding, often seen during the 1st year of menarche. Dysfunctional uterine bleeding occurs due to anovulatory cycles as a result of the immature hypothalamic-pituitary-ovarian (HPO) axis, which fails to produce gonadotropins (LH and FSH) in proper quantities and ratios to induce ovulation. 
  • Precocious puberty: the onset of puberty with the development of external sexual characteristics before 8 years of age. Precocious puberty may result from the early activation of the HPO axis or excess secretion of sex steroids from the ovaries or when obtained from exogenous sources.
  • Delayed puberty: the lack of testicular enlargement in boys by 14 years of age, and the lack of breast development in girls by 13 years of age. The etiology of delayed puberty varies and is generally classified as central or gonadal. Approximately 2.5% of healthy children experience delayed puberty.

References

  1. Herman-Giddens M., et al. (1997). Secondary sexual characteristics and menses in young girls seen in office practice: A study from the Pediatric Research in Office Settings Network. Pediatrics. https://pubmed.ncbi.nlm.nih.gov/9093289/
  2. Tanner, J.M., Davies, P.S. (1985). Clinical longitudinal standards for height and height velocity for North American children. The Journal of Pediatrics. https://pubmed.ncbi.nlm.nih.gov/3875704/
  3. Karpati, A.M., Rubin, C.H., Kieszak, S.M., Marcus, M., Troiano, R.P. (2002). Stature and pubertal stage assessment in American boys: The 1988-1994 Third National Health and Nutrition Examination Survey. The Journal of Adolescent Health. https://pubmed.ncbi.nlm.nih.gov/11869928/ 
  4. Cutler, G.B. Jr, Loriaux, D.L. (1980). Andrenarche and its relationship to the onset of puberty. Federation proceedings. https://pubmed.ncbi.nlm.nih.gov/6445284/

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