Puberty

In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs.

Growth spurts began at around 10-12, but markers of later stages of puberty such as menarche had delays that correlated with severe environmental conditions such as poverty, poor nutrition, air and pollution.

The main steroid hormones, testosterone, estradiol, and progesterone as well as prolactin play important physiological functions in puberty.

However the rate of conversion from testosterone to estradiol (driven by FSH/LH balance) during early puberty is highly individual, resulting in very diverse development patterns of secondary sexual characteristics.

The onset of puberty is associated with high GnRH pulsing, which precedes the rise in sex hormones, LH and FSH.

A result of the social pressure to be thin, the early-maturing females develop a negative view of their body image.

[23] In the past, early onset of puberty in males has been associated with positive outcomes, such as leadership in high school and success in adulthood.

[23] Early-maturing males develop "more aggressive, law-breaking, and alcohol abusing" behaviors, which result in anger towards parents and trouble in school and with the police.

Early puberty also correlates with increased sexual activity and a higher instance of teenage pregnancy, both of which can lead to depression and other psychosocial issues.

[32] Erections during sleep or when waking up are medically known as nocturnal penile tumescence and colloquially referred to as morning wood.

[38][39] During puberty, if not before, the tip and opening of a male's foreskin becomes wider, progressively allowing for retraction down the shaft of the penis and behind the glans, which ultimately should be possible without pain or difficulty.

[40] Research by Øster (1968) found that with the onset and continuation of puberty, the proportion of males able to pull back their foreskins increased.

[50] The first physical sign of puberty in females is usually a firm, tender lump under the center of the areola of one or both breasts, occurring on average at about 10½ years of age.

By another 12 months (stage 4), the breasts are approaching mature size and shape, with areolae and nipples forming a secondary mound.

The mucosal surface of the vagina also changes in response to increasing levels of estrogen, becoming thicker and duller pink in color (in contrast to the brighter red of the prepubertal vaginal mucosa).

[63] During this period, also in response to rising levels of estrogen, the lower half of the pelvis and thus hips widen (providing a larger birth canal).

[52][64] Fat tissue increases to a greater percentage of the body composition than in males, especially in the typical female distribution of breasts, hips, buttocks, thighs, upper arms, and pubis.

[65] Rising levels of androgens can change the fatty acid composition of perspiration, resulting in a more "adult" body odor.

[67] Changes of the vulva initiated by estradiol as well as its direct effects also appear to influence the functioning of the lower urinary tract.

[citation needed] The definition of the onset of puberty may depend on perspective (e.g., hormonal versus physical) and purpose (establishing population normal standards, clinical care of early or late pubescent individuals, etc.).

[73] One possible cause of a delay in the onset of puberty past the age 14 in females and 15 in males is Kallmann syndrome, a form of hypogonadotropic hypogonadism (HH).

Scientists believe the phenomenon could be linked to obesity or exposure to chemicals in the food chain, and is putting females at greater long-term risk of breast cancer.

[79] Various studies have found direct genetic effects to account for at least 46% of the variation of timing of puberty in well-nourished populations.

[73] There is theoretical concern, and animal evidence, that environmental hormones and chemicals may affect aspects of prenatal or postnatal sexual development in humans.

It leaches out of plastic into liquids and foods, and the Centers for Disease Control and Prevention (CDC) found measurable amounts of BPA in the bodies of more than 90 percent of the U.S. population studied.

A simple description of hormonal puberty is as follows: The onset of this neurohormonal process may precede the first visible body changes by 1–2 years.

The pituitary gland responds to the pulsed GnRH signals by releasing LH and FSH into the blood of the general circulation, also in a pulsatile pattern.

The gonads (testes and ovaries) respond to rising levels of LH and FSH by producing the steroid sex hormones, testosterone and estrogen.

[91] Neurons of the arcuate nucleus secrete gonadotropin releasing hormone (GnRH) into the blood of the pituitary portal system.

An American physiologist, Ernst Knobil, found that the GnRH signals from the hypothalamus induce pulsed secretion of LH (and to a lesser degree, FSH) at roughly 1–2 hour intervals.