Normal puberty


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Normal puberty

  1. 1. Normal Puberty
  2. 2. Physiology of Puberty <ul><li>Period of Infancy and Childhood: </li></ul><ul><li>the hypothalamic-pituitary system (the “gonadostat”) is highly sensitive to negative feedback of estrogen (estrodiol concentrations are as low as 10 pg/ml) </li></ul><ul><li>gonadotropins and gonadal steroids remain at very low levels until age 6-8 </li></ul><ul><li>FSH and LH remain low but are still secreted in pulsatility </li></ul>
  3. 3. Physiology of Puberty <ul><li>Prepubertal Period: </li></ul><ul><li>3 critical changes in the low endocrine state of childhood emerge: </li></ul><ul><li>Adrenarche </li></ul><ul><li>Decreasing repression of the “gonadostat” </li></ul><ul><li>Gradual amplification of the GnRH-gonadotropin interaction </li></ul>
  4. 4. Physiology of Puberty <ul><li>Adrenarche (aka Pubarche ) </li></ul><ul><li>Increase in production of adrenal androgens resulting in growth of pubic and axillary hair. </li></ul><ul><li>Precedes menarche by 2 years </li></ul><ul><li>Mechanisms initiating adrenarche are NOT associated with the mechanisms initiating gonadarche </li></ul><ul><li>Evidence </li></ul><ul><li>*Kallman’s syndrome: adrenarche occurs despite absence of gonadarche </li></ul><ul><li>*Addison’s Dz: gonadarche occurs despite absence of adrenarche </li></ul><ul><li>*Precocious Puberty: gonadarche precedes adrenarche </li></ul><ul><li>Initiating Mechanisms: </li></ul><ul><li>Suggested factors: </li></ul><ul><li>Pituitary adrenal androgen stimulating factor </li></ul><ul><li>Local steroid inhibition of key enzymes within the adrenals </li></ul><ul><li>**Mechanisms still remain unclear </li></ul><ul><li>**Adrenarche may be simply the attainment of a level of maturation that requires a particular amount of time. </li></ul>
  5. 5. Physiology of Puberty <ul><li>Decreasing Repression of the “Gonadostat” </li></ul><ul><li>Mechanisms: </li></ul><ul><li>Decreasing the negative feedback of low levels of gonadal estrogen on hypothalamus and pituitary sites </li></ul><ul><li>Decreasing the intrinsic central inhibitory influence on GnRH </li></ul><ul><li>Neuropeptides involved in inhibition: GABA and neuropeptide Y </li></ul>
  6. 6. Physiology of Puberty <ul><li>Alteration of GnRH-Gonadotropin Interactions: </li></ul><ul><li>increased amplitude and frequency of pulsatile GnRH provoke progressively enhanced responses of FSH and LH. </li></ul><ul><li>FSH levels rise, then plateau in midpuberty and LH levels rise slowly, then peak in late puberty </li></ul><ul><li>Increases in gonadotropin secretion stimulates increased secretion of estrogen. </li></ul><ul><li>Dichotomous Effects of Estrogen Feedback </li></ul><ul><li>Positive Feedback: increases LH secretory response to GnRH </li></ul><ul><li>Negative Feedback: combines with inhibin to inhibit FSH response </li></ul>
  7. 7. Timing of Puberty <ul><li>Major Determinant: Genetics </li></ul><ul><li>good correlation of times of menarche of mothers and daughters and between sisters </li></ul><ul><li>Minor Determinant: </li></ul><ul><li>Nutritional status </li></ul><ul><li>general health </li></ul><ul><li>geographic location </li></ul><ul><li>**Children in urban areas, closer to the equator, at lower altitudes, mildly obese start puberty earlier </li></ul><ul><li>Role of Total Body Fat in Timing of Puberty </li></ul><ul><li>-controversial </li></ul><ul><li>Argument: critical body weight must be reached to achieve menarche . </li></ul><ul><li>Supportive Evidence: moderately obese girls have earlier menarche </li></ul><ul><li>Opposing Evidence : morbidly obese girls and intense exercisers with normal weight have delayed menarche </li></ul>
  8. 8. Timing of Puberty <ul><li>Leptin </li></ul><ul><li>proposed hormone responsible for initiation and progression of puberty </li></ul><ul><li>produced by adipocytes </li></ul><ul><li>serum leptin concentration correlated to body fat content </li></ul><ul><li>Observations </li></ul><ul><li>Mice deficient in leptin fail to undergo puberty </li></ul><ul><li>Fertility is restored if leptin-deficient mice are administered the hormone </li></ul><ul><li>Leptin inhibits neuropeptide Y gene expression </li></ul><ul><li>Leptin levels increase in puberty, suggesting a threshold level of leptin (and therefore a critical amount of adipose tissue, the source of leptin) </li></ul><ul><li>*the higher levels of leptin, the earlier the age of menarche </li></ul><ul><li>*girls with idiopathic precocious puberty have higher levels of leptin </li></ul>
  9. 9. Stages of Pubertal Development <ul><li>Pubertal Sequence </li></ul><ul><li>Accelerated growth ->breast development->adrenarche->menarche </li></ul><ul><li>requires 4.5 years (range 1.5 to 6 years) </li></ul>
  10. 10. Signs of Puberty: Tanner Staging Stage 1 (Prepubertal) Elevation of papilla only. No pubic hair. Stage 2 Elevation of breast and papilla as small mound, areola diameter enlarged. Median age: 9.8 Sparse, long, pigmented hair, along labia majora. Median age: 10.5 Stage 3 Further enlargement without separation of breast and areola. Median age: 11.2 Dark, course, curled hair sparsely spread over mons. Median age: 11.4 Stage 4 Secondary mound of areola and papilla above the breast. Median age: 12.1 Adult type hair, abundant but limited to mons. Median age: 12 Stage 5 Recession of areola to contour of breast. Median age: 14.6 Adult type spread in quantity and distribution. Median age: 13.7
  11. 11. Tanner Staging
  12. 12. Growth <ul><li>average girl reached growth peak 2 years after breast budding and one year prior to menarche </li></ul><ul><li>*limited growth potential after menarche </li></ul><ul><li>due to estrogen and concomitant increase in growth hormone </li></ul><ul><li>peak bone mineralization occurs as well. </li></ul><ul><li>*half total body calcium laid down during puberty . </li></ul><ul><li>calcium supplementation during adolescence results in increase bone density </li></ul><ul><li>(GIVES PROTECTION AGAINT FUTURE OSTEOPOROSIS!!) </li></ul>
  13. 13. Menarche <ul><li>age of menarche chiefly controlled by genetics </li></ul><ul><li>environmental factors important: improving nutrition produces taller, heavier girls </li></ul><ul><li>Trend toward lowering the menarchal age and puberty halted in the 1960s. </li></ul><ul><li>Median age of menarche in U.S. is 12.8 </li></ul><ul><li>Menses are usually anovulatory for 12-18 months after menarche </li></ul>