Adolescence

Adolescence is a human life stage spanning the transition between childhood and adulthood. It involves rapid physical and emotional change. The World Health Organization considers adolescents to be individuals of ages 10 to 19 years. In physiological terms, adolescence can be defined as the period beginning with secretion of pituitary and hypothalamic hormones that stimulate development of reproductive organs. Adolescence ends when full adult height is reached. Often adolescence is defined more narrowly as puberty, which physiologically is the first several years of adolescence. Puberty is the stage of development when the human body becomes capable of reproduction. Puberty ends in females when they experience their first menstrual period and in males with their first ejaculation of viable sperm. In North America girls typically hit puberty at around 11 to 12 years and boys at 12 to 13 years. The onset of puberty varies depending on genetics of the parents, as well as environmental factors, such as nutrition and overall health. Adolescents living in areas in which there is access to balanced nutrition may undergo puberty earlier than adolescents in areas with minimal nutrition. Physical changes of adolescence continue for many years after puberty.

Adolescence also includes significant cognitive developments, such as the development of systematic thinking or strategic thinking about problem-solving. These rapid transformations typically affect emotions and behaviors as individuals adapt to their developing bodies. The onset of adolescence can vary significantly across individuals, both within and between different cultures.

Adolescence involves very different changes in females and males. In both, these are hormone-driven effects leading to sexual maturation. In both sexes, the maturing hypothalamus secretes rising levels of gonadotropin-releasing hormone. Gonadotropin-releasing hormone (GnRH) triggers the secretion by the pituitary of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). In females, FSH causes ovarian follicles to develop. Ovarian follicles secrete estrogen, progesterone, inhibin, and some androgen. Androgen and estrogen are classes of hormones, while progesterone and inhibin are more specific. Estrogens, particularly estradiol, and androgens stimulate most physical changes in females undergoing puberty. Onset of puberty begins with breast development, or thelarche, triggered by estrogen, progesterone, and prolactin. Breast development continues until approximately age 20. After thelarche comes pubarche. Triggered by androgens, pubarche marks the growth of pubic and axillary hair (hair under the armpit) and the development of sebaceous and axillary glands. Androgens also stimulate the libido (sex drive). Menarche is next—the first menstrual period. Sufficient fat stores are required to support pregnancy. Menstruation is not reached in females with little body fat (typically less than 17 percent) and typically ceases in females with less than 22 percent body fat. Estradiol triggers many other changes, including growth of ovaries and secondary sex organs, as well as rapid increase in height. The pelvis widens, and fat is deposited in breasts, buttocks, thighs, hips, labia majora, and the mons pubis. Progesterone prepares the uterus for possible pregnancy.