The onset of pubertal changes usually happen between 10 and 16 years of age. In the United states, the mean age of menarche is approximately 12,4 years. The pubertal changed is determined primarily by genetic factors, but is also influenced by geographic location, and nutrional status. During this transition, a variety of physical, endocrinologic, and psychologic changes accompany the increasing levels of sex steroids.

There are many factor influence pubertal development;

1. Geographic location.
   The Girls in metropolitan areas, at altituded near sea level, or at latitudes close to the equator tend to begin puberty at an earlier age.
2. Nutrional status.
   Malnutrition and chronic illness have a later onset of menses.
   Obese children have an earlier onset.
3. Exercise.
   Excessive exercise relative to the caloric intake can also delay the onset of puberty.
4. Psychological factors.
   Severe neurotic as well as chronic isolation may interfere with the normal onset of puberty through a mechanism similar to adult hypothalamic amenorrhea.

Pubertal Onset
During the transition ( approximately the 11 year of life), there is a gradual loss of sensitivity by the gonadostat to the negative feedback of sex steroids. GnRH pulses (with their mirroring pulses of FSH and LH) increase in amplitude and frequency as a consequence of this reduce negative feedback effect.

Leptin (produced by adipocytes) that mediates appetite satiety, precedes and is necessary for reduce the sensitivity of the gonadostat. Combination the loss of intrinsic central nervous system inhibition of hypothalamic GnRH release and a further decrease in sensitivity of the gonadostat is heralded by prominet sleep-associated increase in GnRH secretion. The development of secondary sexual characteristics are induced by ovarian follicular maturation and sex steroid production. (the doctor rend-san)