Puberty

Puberty marks the physical transition from childhood to adulthood. While the changes that accompany this time are significant, their onset, rate, and duration vary from person to person. In general, these changes are either sexual or growth related. The pubertal growth spurt is characteristic of primates. Although other mammals may have increased reproductive organ growth, their overall size does not increase as dramatically. The major control center for human pubertal development is the hypothalamus for both sexes, but puberty is accompanied by additional growth of the adrenal glands, as well. The added adrenal tissue secretes the sex hormones, androgens or estrogens, at low levels. The adrenal sex hormones are thought to initiate the growth of pubic and axillary (under-arm) hair. This adrenal maturation is called adrenarche.

It is not known exactly what triggers puberty to begin. However, the hypothalamus sends out gonadotropin hormones responsible for sperm and egg maturation. One theory holds that normal brain growth towards the end of childhood includes significant hypothalamic changes. Hypothalamic receptors are thought to become more sensitive to low levels of circulating sex steroids. These changes enable the neuroendocrine system to initiate spermarche (sperm maturation) and menstruation in puberty. However, these early hormonal fluctuations begin at night and remain a nocturnal pulse for some time before they are detectable while awake. Some behavioral changes are related to pubertal hormonal changes, as well. The increase in testosterone is associated with more aggressive behavior in males. And libido (sex drive) increases occur for some teenagers in association with estrogen and testosterone increases. These effects are also carried out through sex hormone receptors on the hypothalamus.