Human puberty period
Human puberty is defined as the transition between the juvenile state and the mature reproductive state when secondary sex characteristics develop and fertility is achieved. It is composed of the relatively synchronous processes of adrenarche and gonadarche. Adrenarche occurs usually one to two years before gonadarche and is independent of gonadarche. Children without functioning gonads will achieve adrenarche. Puberty includes the adolescent growth spurt, growth of pubic and axillary hair in males and females, and specific secondary sex characteristics for males and females.
Adrenarche: The increase in secretion of androgens by the adrenal gland, occurring from about age 5 to age 20
Gonadarche: The initiation of production of significant amount of sex steroids by the testis or the ovary related to stimulation by gonadotropins
Puberty in Females
The earliest manifestation of puberty in females is adrenarche. The rise in serum DHEA and DHEAS may have no clinical signs or symptoms; therefore, the first sign of puberty in females is usually defined as the initiation of breast buds. The breast develops under unopposed low dose estrogen stimulation for about two years before the first menses. During this time, pubic and axillary hair become evident and there is a growth spurt. Weight gain occurs with increase in height, but there is also an increase in body fat as distributed in the breasts, mons pubis, hips and thighs. The vagina lengthens and becomes rugated, and the labia majora and minora become thickened and rugated.
The first menses occurs about two years after breast bud development and is usually the result of fluctuating estrogens associated with follicle development without ovulation. Ovulation usually occurs within six months from the first episode of vaginal bleeding. The breast and pubic hair development as well as vertical growth and fat deposition continue for several years after the first menses.
Puberty in Males
As in females, puberty begins with adrenarche that also has limited clinical manifestations in boys. The first clinical manifestation is testicular enlargement, which begins at a mean age of 11.6 and is followed in the next two years by pubic hair. Adult size and shape of the penis and scrotum is achieved between ages 12 and 17 with an average of about 15 years of age, and pubic hair completes development at about the same time.
The testosterone effect on the vocal cords leads to the beginnings of voice changing at an average age of 13, accompanied by the onset of spermatogenesis. The growth spurt continues with 45 % of the adult skeletal mass acquired between age 11 and age 18. Prior to puberty, males and females have similar muscle mass; but by the end of puberty, the average male has more muscle mass than the average female.
The emotional responses to the changes in gonadal steroid are poorly understood, although all families and societies describe a marked change in pubertal children with respect to their relationships with their parents, peers and members of the opposite gender. Violent events by males increase dramatically in adolescence, but whether this is a direct effect of gonadal steroids on behavior or a function of the individual adolescent’s character and societal roles is not clear.
Errors in Puberty (Delayed Puberty)
Delayed puberty may be due to dysfunction of the hypothalamic/pituitary axis, end organ failure, or may be idiopathic. Constitutional delay of puberty may be due to chronic severe medical illness, weight loss or malnourishment, or physical stress (including chronic strenuous exercise).
Adrenarche usually occurs, but gonadarche does not follow. Delayed puberty may also be due to pituitary or hypothalamic tumors, pituitary failure, or congenital absence of GNRH neurons.
Gonadal failure in boys or girls may be due to chromosomal anomalies (Turner’s syndrome), exposure to high dose chemotherapy or radiation to the pelvis in childhood, autoimmune or idiopathic. Adrenarche also still occurs (except in those children with pituitary and subsequent adrenal failure), but development of secondary sex characteristics does not follow. An evaluation of delayed puberty should be evaluated in girls who have no evidence of breast development by age 14 and in boys who have no evidence of genital growth by age 15.