Puberty

• Puberty


  The stage of physical maturation in which an individual becomes physiologically capable of sexual reproduction
• Puberty


  The stage in life when an individual begins to be physiologically competent to proliferate (i.e begin to become an adult)
• Adolescence


  The transition period between childhood and adulthood
• Puberty starts because of sex hormones
• Puberty


  Period when the gonads grow rapidly, output of sex hormones leads to the development of secondary sexual characters and mature gamates are released for the first time
• Signs of puberty in girls

  • Pubic hair growth and breast development precede menarche by about two years
• Signs of puberty in boys

  • About 5% of boys show some signs of puberty at the age of 10 years
  • 5% of normal boys show no signs until they are 15 years old
• Menarche


  The first menstruation
• Puberty is partially genetically determined
• Nutrition is very important in modifying pubertal timing
• In most industrial nations, the timing of menarche has been advancing by about 4-6 months per decade since the mid 19th century
• Artificially long days have been known to advance puberty in animals
• In blind girls menarche is significantly earlier than normal ones
• Continual bombardment of the nervous system with erotica can also advance puberty
• Adrenals and gonads


  Both are concerned with puberty
• Mechanism of puberty


  1. In childhood the output of gonadal steroids and adrenal androgens is low

  2. Before puberty, tiny amounts of steroids produced by the prepubertal gonad is enough to inhibit gonadotrophin output

  3. At puberty the sensitivity of the hypothalamus to the steroids diminishes

  4. Amount of steroids are no longer enough to inhibit gonadotrophin output and so this (FSH,LH,and Prolactin) rises
• The growth spurt in puberty begins in about the 8th year of life and usually culminates in the onset of puberty and menstruation between the ages of 11 and 16 years in girls (Average 13 years)
• Growth spurt in puberty

  • Before puberty there is relatively little difference between the average heights and weights of girls and boys
  • Between the ages of 8 and 13, girls tend to be heavier than boys of similar age because of the earlier pubertal growth spurt before menarche
  • Little growth occurs afterwards. Boys are finally taller than girls
  • Appearance of pubic hair and growth spurt are associated with adrenal androgens
  • In the male, testicular androgens modify the distribution of pubic hair and forehead hair line and increase the intensity of the spurt
• Hormonal changes of puberty

  • Gonadotropic-Releasing Hormone
  • Gonadotropins
  • Adrenal steroids
  • Ovarian development
  • Testis development
  • Role of GH, IGF-I and insulin
  • Leptin
• Physiology of puberty


  • The biological changes include: neurosecretory factors and/or hormones modulation of somatic growth
  • Initiation of the development of the sex glands
• Physiology of puberty


  1. Activation of the hypothalamic-pituitary gonadal axis induces and enhances the progressive ovarian and testicular sex hormone secretion

  2. Responsible for the profound biological, morphological, and psychological changes to which the adolescent is subjected

  3. Sex steroid production leads to the appearance and maintenance of sexual characteristics and capacity for reproduction
• Puberty stages (Tanner)


  • Puberty proceeds through five stages from childhood to full maturity (P1 to P5) as described by Marshall and Tanner
  • These stages reflect the progressive modifications of the external genitalia and of sexual hair
  • Secondary sex characteristics appear at a mean age of 10.5 years in girls and 11.5 to 12 years in boys
• Uterine development


  The prepubertal uterus is tear-drop shaped, with the neck and isthmus accounting for up to two-thirds of the uterine volume; then, with the production of estrogens, it becomes pear shaped, with the uterine body increasing in length and thickness proportionately more than the cervix
• Menarche


  • During puberty, plasma estradiol levels fluctuate widely, probably reflecting successive waves of follicular development that fail to reach the ovulatory stage
  • The uterine endometrium is affected by these changes and undergoes cycles of proliferation and regression, until a point is reached when substantial growth occurs so that withdrawal of estrogen results in the first menstruation
• Ovulation


  1. Under the influence of FSH and LH, the secondary follicle develops rapidly to a diameter of 25 mm. with sudden increase in LH that causes the primary oocyte to complete meiosis I and the follicle to enter the pre- ovulatory stage

  2. Meiosis II then commences, but the oocyte is halted in metaphase about 3 hours before ovulation

  3. Meanwhile, the surface of the ovary begins to bulge locally, and at the apex, an avascular spot, the stigma, appears

  4. The high concentration of LH increases collagenase activity,resulting in digestion of collagen fibers surrounding the follicle

  5. Prostaglandin levels also increase in response to the LH surge and cause local muscular contractions in the ovarian wall

  6. Those contractions extrude the oocyte, which together with its surrounding granulosa cells from the region of the cumulus oophorus, breaks free and floats out of the ovary this process is referred to as ovulation

  7. Some of the cumulus oophorus cells then rearrange themselves around the zona pellucida to form the corona radiata
• Plasma testosterone levels also increase at puberty although not as markedly as in males
• Plasma progesterone remains at low levels even if secondary sexual characteristics have appeared
• A rise in progesterone after menarche is, in general, indicative that ovulation has occured
• The first ovulation does not take place until 6-9 months after menarche because the positive feedback mechanism of estrogen is not developed
• Female secondary sexual characteristics

  If breast development, pubic and/or axillary hair, and menses occur earlier than normal variations from the mean, the terms premature thelarche, pubarche and/or adrenarche, and menarche are used
• Pubertal stages (Tanner) male

  • P1 Prepubertal, testicular length less than 2.5cm
  • P2 Early increase in testicular size, scrotum slightly pigmented, few long and dark pubic hair
  • P3 Testicular length 3.3-4 cm, lenghtening of the penis, increase in pubic hair
  • P4 Testicular length 4.1-4.5cm, increase in length and thickening of the penis, adult amount of pubic hair
  • P5 Testicular length greater than 4.5cm, full spermatogenesis
• Puberty: male


  • Secondary sexual development in boys begins around 11-12 years of age
  • Growth kinetics are enhanced from early puberty on
  • Maximal velocity is attained only around 14 to 15 years of age
  • Testis increases in size, mainly at the expense of the seminiferous tubules
  • The interstitial (Leydig) cells develop and ensure synthesis and secretion of testosterone
• Testes development 1


  • The increase in testicular size observed during prepuberty and puberty results essentially from the development of the seminiferous tubules under the stimulating effect of FSH
  • The testicular volume increases throughout puberty up to Tanner stage P4 when a longitudinal diameter of 5.0 + 0.5 cm or a volume of 17.6 + 4.0 ml is reached
• Testes development 2


  • Long-standing pulsatile LH secretion induces the differentiation of interstitial cells into testosterone-secreting Leydig cells, which, in turn, exert a negative feedback control on LH secretion
  • As puberty progresses, spermatogenesis is initiated and then sustained by FSH and by testosterone produced by the Leydig cells under LH control
• A significant increase of plasma testosterone is found only between Tanner pubertal stages P3 and P4
• Dihydrotestosterone shows a pattern similar to that of testosterone, and the proportion of dihydrotestosterone to testosterone decreases gradually until adulthood, when dihydrotestosterone levels are approximately 10% of those of testosterone
• Puberty is completed usually within 3 to 4 years of its onset, and the final height resulting from complete fusion of the epiphyses occurs within approximately 2 years after menarche
• Chronological aspect of puberty in girls

  • Acceleration of growth rate
  • Development of breasts and pubic hair
  • Axillary hair
  • Menarche
• Chronological aspect of puberty in boys

  • Increase of penile length
  • Pubic hair
  • Increased growth rate
  • Axillary hair
  • Deepening of the voice
  • Increase of testicular volume
• Hormonal changes: prepubertal children

  No significant luteinizing hormone (LH) or follicle-stimulating hormone (FSH) response to intravenous or subcutaneous administration of GnRH is observed