Puberty is the period, which links childhood to adulthood. It is the period of gradual development of secondary sexual characters. There are profound biological, morphological, and psychological changes that lead to full sexual maturity and eventually fertility.
As described by Tanner and Marshall, five important physical changes are evident during puberty. These are breast, pubic and axillary hair growth, growth in height, and menstruation. Most of the changes occur gradually but only the menarche can be dated. Moreover, there is a lot of variations in the timing of the events.
Growth of height in an adolescent girl is mainly due to hormones. The important hormones are growth hormone, estrogen, and insulin-like growth factor-1 (IGF-1). The bone or skeletal age is determined by X-ray of hand or knee.
The levels of gonadal steroids and gonadotropins (FSH, LH) are low until the age of 6-8 years. This is mainly due to the negative feedback effect of estrogen to the hypothalamic pituitary system (gonadostat). The gonadostat remains very sensitive (6-15 times) to the negative feed-back effect, even though the level of estradiol is very low (10 pg/mL) during that time. As puberty approaches this negative feedback effect of estrogen is gradually lost. This results in some significant changes in the endocrine function of the girl.
The onset of first menstruation in life is called menarche. It may occur anywhere between 10 and 16 years, the peak time being 13 years. There is endometrial proliferation due to ovarian estrogen but when the level drops temporarily, the endometrium sheds and bleeding is visible. It denotes an intact hypothalamic pituitaryovarian axis, functioning ovaries, presence of responsive endometrium to the endogenous ovarian steroids and the presence of a patent uterovaginal canal. The first periodvis usually anovular. The ovulation may be irregular for a variable period following menarche and may take about 2 years for regular ovulation to occur. The menses may be irregular to start with.
The gonadotropin-releasing hormone (GnRH) pulses from hypothalamus results in pulsatile gonadotropin secretion (first during the night then by the day time). The tonic and episodic secretion of gonadotropins in prepubertal period is gradually changed to one of cyclic release in postpubertal period. Thyroid gland plays an active role in the hypothalamopituitary gonadal axis. Adrenal glands (adrenarche) increase their activity of sex steroid synthesis (androstenedione, dehydroepi- androsterone (DHA), dehydroepiandrosterone sulfate (DHAS) from about 7 years of age. Increased sebum formation, pubic and axillary hair, and change in voice are primarily due to adrenal androgen production. Gonadarche increased amplitude and frequency of GnRH, which increases the secretion of FSH and LH this causes ovarian follicular development and increase in estrogen level. Gonadal estrogen is responsible for the development of uterus, vagina, vulva, and also the breasts. Leptin, a peptide, secreted in the adipose tissue is also involved in pubertal changes and menarche. Leptin is important for feedback involving GnRH and LH pulsatility. Leptin plays a major link between body composition (body fat proportion).
Ovaries change their shape, the elongated shape becomes bulky and oval. The ovarian bulk is due to follicular enlargement at various stages of development and proliferation of stromal cells. The uterine body and the cervix ratio at birth is about 1:2, the ratio becomes 1:1 when menarche occurs. Thereafter, the enlargement of the body occurs rapidly, so that the ratio soon becomes 2:1. The vaginal changes are more pronounced. A few layers of thin epithelium in a child become stratified epithelium of many layers. The cells are rich in glycogen due to estrogen. Doderlein's bacilli appear which convert glycogen into lactic acid; the vaginal pH becomes acidic, ranging between 4 and 5.
The vulva is more reactive to steroid hormones. The mons pubis and the labia minora increase in size. Breast changes are pronounced. Under the influence of estrogen, there is marked proliferation of duct systems and deposition of fat. The breast becomes prominent and round. Under the influence of progesterone, the development of acini increases considerably.
Important controlling factors for onset of puberty are genetic, nutrition, body weight, psychologic state, social and cultural background, and exposure to light and others. A girl, living in urban areas with good nutrition, adequate body weight and whose mother and sisters have early menarche, starts puberty early. Blind girls start menarche early.
The term precocious puberty is reserved for girls who exhibit any secondary sex characteristics before the age of 8 (before age 7 in whites) or menstruate before the age of 10. Precocious puberty may be isosexual where the features are due to excess production of estrogen. It may be heterosexual where features are due to excess production of androgen (from ovarian and adrenal neoplasm). Precocious puberty is more common in girls (20 times) than boys.
Premature pubarche is isolated development of axillary and/or pubic hair prior to the age of 8 without other signs of precocious puberty. The premature hair growth may be due to unusual sensitivity of end organs to the usual low level of hormones in the blood during childhood. Rarely, there may be signs of excess androgen production due to adrenal hyperplasia or tumor or androgenic ovarian tumor (Leydig cell tumor, androblastoma, etc.).
Premature menarche is an isolated event of cyclic vaginal bleeding without any other signs of secondary sexual development. The cause remains unclear but may be related to unusual endocrine sensitivity of the endometrium to the low level of estrogens. Chorionic epithelioma, hepatoblastoma are the ectopic sources of human chorionic gonadotropin and may cause sexual precocity.
Puberty is said to be delayed when the breast tissue and/or pubic hair have not appeared by 13-14 years or menarche appears as late as 16 years. The normal upper age limit of menarche is 15 years. It is more common in boys than in girls. Before the onset of menarche, pubertal (Tanner stage 1 through 5) changes are breast budding followed within few months by the appearance of pubic hair. Breast budding is the earliest sign and menarche is the latest sign of puberty. Onset of menarche is related to body composition (ratio of body fat to total body weight) rather than total body weight. Moderately obese girls between 20% and 30% above the ideal body weight have earlier onset of menarche. Malnutrition is known to delay the onset of puberty.
