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In humans, puberty is the process of physical changes by which a child's body becomes an adult body capable of reproduction. Puberty is initiated by hormone signals from the brain to the gonads (the ovaries and testes). In response, the gonads produce a variety of hormones that stimulate the growth, function, or transformation of brain, bones, muscle, skin, breasts, and reproductive organs. Growth accelerates in the first half of puberty and stops at the completion of puberty. Before puberty, body differences between boys and girls are almost entirely restricted to the genitalia. During puberty, major differences of size, shape, composition, and function develop in many body structures and systems. The most obvious of these are referred to as secondary sex characteristics.

In a strict sense, the term puberty (derived from the Latin word puberatum (age of maturity, manhood)) refers to the bodily changes of sexual maturation rather than the psychosocial and cultural aspects of adolescent development. Adolescence is the period of psychological and social transition between childhood and adulthood. Adolescence largely overlaps the period of puberty, but its boundaries are less precisely defined and it refers as much to the psychosocial and cultural characteristics of development during the teen years as to the physical changes of puberty.

Contents

Differences between male and female puberty

Two of the most significant differences between puberty in girls and puberty in boys are the age at which it begins, and the major sex steroids involved.

Approximate outline of development periods in child and teenager development. Puberty is marked in green at right.

Although there is a wide range of normal ages, girls typically begin the process of puberty at age 10, boys at age 12.[1] Girls usually complete puberty by ages 15-17, while boys usually complete puberty by ages 17 or 18.[2][3] Any increase in height beyond these ages is uncommon. Girls attain reproductive maturity about 4 years after the first physical changes of puberty appear.[4] In contrast, boys accelerate more slowly but continue to grow for about 6 years after the first visible pubertal changes.[5]

1 Follicle-stimulating hormone - FSH
2 Luteinizing hormone - LH
3 Progesterone
4 Estrogen
5 Hypothalamus
6 Pituitary gland
7 Ovary
8 Pregnancy - hCG (Human chorionic gonadotropin)
9 Testosterone
10 Testicle
11 Incentives
12 Prolactin - PRL

In males, testosterone, an androgen, is the principal sex hormone. While testosterone produces all the male changes characterized as virilization, a substantial product of testosterone metabolism in males is estradiol, though levels rise later and more slowly than in girls. The male "growth spurt" also begins later, accelerates more slowly, and lasts longer before the epiphyses fuse. Although boys are on average 2 cm shorter than girls before puberty begins, adult men are on average about 13 cm (5.2 inches) taller than women. Most of this sex difference in adult heights is attributable to a later onset of the growth spurt and a slower progression to completion, a direct result of the later rise and lower adult male levels of estradiol.[6]

The hormone that dominates female development is estradiol, an estrogen. While estradiol promotes growth of breasts and uterus, it is also the principal hormone driving the pubertal growth spurt and epiphyseal maturation and closure.[7] Estradiol levels rise earlier and reach higher levels in women than in men.

Puberty onset

The onset of puberty is associated with high GnRH pulsing, which precedes the rise in sex hormones, LH and FSH.[8] Exogenous GnRH pulses cause the onset of puberty.[9] Brain tumors which increase GnRH output may also lead to premature puberty[10]

The cause of the GnRH rise is unknown. Leptin might be the cause of the GnRH rise. Leptin has receptors in the hypothalamus which synthesizes GnRH.[11] Individuals who are deficient in leptin fail to initiate puberty.[12] The levels of leptin increase with the onset of puberty, and then decline to adult levels when puberty is completed. The rise in GnRH might also be caused by genetics. A study[13] discovered that a mutation in genes encoding both Neurokinin B as well as the Neurokinin B receptor can alter the timing of puberty. The researchers hypothesized that Neurokinin B might play a role in regulating the secretion of Kisspeptin, a compound responsible for triggering direct release of GnRH as well as indirect release of LH and FSH.

Physical changes in boys

Testicular size, function, and fertility

In boys, testicular enlargement is the first physical manifestation of puberty (and is termed gonadarche).[14] Testes in prepubertal boys change little in size from about 1 year of age to the onset of puberty, averaging about 2–3 cm in length and about 1.5–2 cm in width. Testicular size continues to increase throughout puberty, reaching maximal adult size about 6 years after the onset of puberty. After the boy's testicles have enlarged and developed for about one year, the length and then the breadth of the shaft of the penis will increase and the glans penis and corpora cavernosa will also start to enlarge to adult proportions.[15] While 18–20 cc is an average adult size, there is wide variation in testicular size in the normal population[16]

The testes have two primary functions: to produce hormones and to produce sperm. The Leydig cells produce testosterone, which in turn produces most of the male pubertal changes. Most of the increasing bulk of testicular tissue is spermatogenic tissue (primarily Sertoli and Leydig cells). Sperm can be detected in the morning urine of most boys after the first year of pubertal changes, and occasionally earlier[citation needed]. On average, potential fertility in boys is reached at 13 years old, but full fertility will not be gained until 14–16 years of age[citation needed].

Pubic hair

Pubic hair often appears on a boy shortly after the genitalia begin to grow. In girls, the first appearance of pubic hair is termed pubarche. The pubic hairs are usually first visible at the dorsal (abdominal) base of the penis. The first few hairs are described as stage 2. Stage 3 is usually reached within another 6–12 months, when the hairs are too many to count. By stage 4, the pubic hairs densely fill the "pubic triangle." Stage 5 refers to spread of pubic hair to the thighs and upward towards the navel as part of the developing abdominal hair.

Body and facial hair

Facial hair of a male that has been shaved

In the months and years following the appearance of pubic hair, other areas of skin that respond to androgens may develop androgenic hair. The usual sequence is: underarm (axillary) hair, perianal hair, upper lip hair, sideburn (preauricular) hair, periareolar hair, and the beard area.[17] As with most human biological processes, this specific order may vary among some individuals. Arm, leg, chest, abdominal, and back hair become heavier more gradually. There is a large range in amount of body hair among adult men, and significant differences in timing and quantity of hair growth among different ethnic groups.[1] Facial hair is often present in late adolescence, but may not appear until significantly later.[18][19] Facial hair will continue to get coarser, darker and thicker for another 2–4 years after puberty.[18] Some men do not develop full facial hair for up to 10 years after the completion of puberty.[18] Chest hair may appear during puberty or years after.[1] Not all men have chest hair.

Voice change

Under the influence of androgens, the voice box, or larynx, grows in both sexes. This growth is far more prominent in boys, causing the male voice to drop and deepen, sometimes abruptly but rarely "over night," about one octave, because the longer and thicker vocal folds have a lower fundamental frequency. Before puberty, the larynx of boys and girls is about equally small.[20] Occasionally, voice change is accompanied by unsteadiness of vocalization in the early stages of untrained voices. Most of the voice change happens during stage 3-4 of male puberty around the time of peak growth. Full adult pitch is attained at an average age of 15 years[citation needed]. It usually precedes the development of significant facial hair by several months to years.

Male musculature and body shape

By the end of puberty, adult men have heavier bones and nearly twice as much skeletal muscle. Some of the bone growth (e.g., shoulder width and jaw) is disproportionately greater, resulting in noticeably different male and female skeletal shapes. The average adult male has about 150% of the lean body mass of an average female, and about 50% of the body fat.

This muscle develops mainly during the later stages of puberty, and muscle growth can continue even after a male is biologically adult. The peak of the so-called "strength spurt," the rate of muscle growth, is attained about one year after a male experiences his peak growth rate.

Often, the fat pads of the male breast tissue and the male nipples will develop during puberty; sometimes, especially in one breast, this becomes more apparent and is termed gynecomastia. It is usually not a permanent phenomenon.

Body odor and acne

Rising levels of androgens can change the fatty acid composition of perspiration, resulting in a more "adult" body odor. As in girls, another androgen effect is increased secretion of oil (sebum) from the skin and the resultant variable amounts of acne. Acne can not be prevented or diminished easily, but it typically fully diminishes at the end of puberty. However, it is not unusual for a fully grown adult to suffer the occasional bout of acne, though it is normally less severe than in adolescents. Some may desire using prescription topical creams or ointments to keep acne from getting worse, or even oral medication, due to the fact that acne is emotionally difficult and can cause scarring.

Physical changes in girls

Breast development

The first physical sign of puberty in girls is usually a firm, tender lump under the center of the areola of one or both breasts, occurring on average at about 10.5 years of age.[21] This is referred to as thelarche. By the widely used Tanner staging of puberty, this is stage 2 of breast development (stage 1 is a flat, prepubertal breast). Within six to 12 months, the swelling has clearly begun in both sides, softened, and can be felt and seen extending beyond the edges of the areolae. This is stage 3 of breast development. By another 12 months (stage 4), the breasts are approaching mature size and shape, with areolae and papillae forming a secondary mound. In most young women, this mound disappears into the contour of the mature breast (stage 5), although there is so much variation in sizes and shapes of adult breasts that stages 4 and 5 are not always separately identifiable.[22]

Pubic hair

Pubic hair is often the second noticeable change in puberty, usually within a few months of thelarche.[23] It is referred to as pubarche. The pubic hairs are usually visible first along the labia. The first few hairs are described as Tanner stage 2.[22] Stage 3 is usually reached within another 6–12 months, when the hairs are too numerous to count and appear on the pubic mound as well. By stage 4, the pubic hairs densely fill the "pubic triangle." Stage 5 refers to spread of pubic hair to the thighs and sometimes as abdominal hair upward towards the navel. In about 15% of girls, the earliest pubic hair appears before breast development begins.[23]

Vagina, uterus, ovaries

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).[24] Whitish secretions (physiologic leukorrhea) are a normal effect of estrogen as well.[21] In the two years following thelarche, the uterus, ovaries, and the follicles in the ovaries increase in size.[25] The ovaries usually contain small follicular cysts visible by ultrasound.[26][27]

Menstruation and fertility

The first menstrual bleeding is referred to as menarche, and typically occurs about two years after thelarche.[23] The average age of menarche in girls is 11.75 years.[23] The time between menstrual periods (menses) is not always regular in the first two years after menarche.[28] Ovulation is necessary for fertility, but may or may not accompany the earliest menses.[29] In postmenarchal girls, about 80% of the cycles were anovulatory in the first year after menarche, 50% in the third year and 10% in the sixth year.[28] Initiation of ovulation after menarche is not inevitable. A high proportion of girls with continued irregularity in the menstrual cycle several years from menarche will continue to have prolonged irregularity and anovulation, and are at higher risk for reduced fertility.[30] Nubility is used to designate achievement of fertility.

Body shape, fat distribution, and body composition

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).[22][31] 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. Progressive differences in fat distribution as well as sex differences in local skeletal growth contribute to the typical female body shape by the end of puberty. On average, at 10 years, girls have 6% more body fat than boys.[32]

Body odor and acne

Rising levels of androgens can change the fatty acid composition of perspiration, resulting in a more "adult" body odor. This often precedes thelarche and pubarche by one or more years. Another androgen effect is increased secretion of oil (sebum) from the skin. This change increases the susceptibility to acne, a skin condition that is characteristic of puberty.[33] Acne varies greatly in its severity.[33]

Variations

Timing of the onset of puberty

The definition of the onset of puberty depends on perspective (e.g., hormonal versus physical) and purpose (establishing population normal standards, clinical care of early or late pubescent individuals, etc.) The most commonly used definition of the onset of puberty is physical changes to a person's body[citation needed]. These physical changes are the first visible signs of neural, hormonal, and gonadal function changes.

The age at which puberty begins varies between individuals and populations. The age at which puberty begins is affected by both genetic factors and by environmental factors such as nutritional state and social circumstances.[1] An example of social circumstances is the Vandenbergh effect; a juvenile female who has significant interaction with adult males will enter puberty earlier than juvenile females who are not socially overexposed to adult males.[34]

The average age at which puberty begins is affected by race. For example, the average age of menarche in various populations surveyed has ranged from 12 to 18 years. The earliest average onset of puberty is for African-American girls and the latest average onset for high altitude subsistence populations in Asia. However, much of the higher age averages reflect nutritional limitations more than genetic differences and can change within a few generations with a substantial change in diet. The median age of menarche for a population may be an index of the proportion of undernourished girls in the population, and the width of the spread may reflect unevenness of wealth and food distribution in a population.

Researchers have identified an earlier age of the onset of puberty. However, they have based their conclusions on a comparison of data from 1999 with data from 1969. In the earlier example, the sample population was based on a small sample of white girls (200, from Britain). The later study identified as puberty as occurring in 48% of African-American girls by age nine, and 12% of white girls by that age.[35]

Historical shift

The average age at which the onset of puberty occurs has dropped significantly since the 1840s.[36][37][38] Researchers refer to this drop as the 'secular trend'. In every decade from 1840 to 1950 there was a drop of four months in the average age of menarche among Western European females. In Norway, girls born in 1840 had their menarche at an average age of 17 years. In France the average in 1840 was 15.3 years. In England the average in 1840 was 16.5 years. In Japan the decline happened later and was then more rapid: from 1945 to 1975 in Japan there was a drop of 11 months per decade.

Genetic influence and environmental factors

Various studies have found direct genetic effects to account for at least 46% of the variation of timing of puberty in well-nourished populations.[39][40][41][42] The genetic association of timing is strongest between mothers and daughters. The specific genes affecting timing are not yet known.[39] Among the candidates is an androgen receptor gene.[43]

Researchers[44] have hypothesized that early puberty onset may be caused by certain hair care products containing estrogen or placenta, and by certain chemicals, namely phthalates, which are used in many cosmetics, toys, and plastic food containers.

If genetic factors account for half of the variation of pubertal timing, environment factors are clearly important as well. One of the first observed environmental effects is that puberty occurs later in children raised at higher altitudes. The most important of the environmental influences is clearly nutrition, but a number of others have been identified, all which affect timing of female puberty and menarche more clearly than male puberty.

Hormones and steroids

There is theoretical concern, and animal evidence, that environmental hormones and chemicals may affect aspects of prenatal or postnatal sexual development in humans.[45] Large amounts of incompletely metabolized estrogens and progestagens from pharmaceutical products are excreted into the sewage systems of large cities, and are sometimes detectable in the environment. Sex steroids are sometimes used in cattle farming but have been banned in chicken meat production for 40 years. Although agricultural laws regulate use to minimize accidental human consumption, the rules are largely self-enforced in the United States. Significant exposure of a child to hormones or other substances that activate estrogen or androgen receptors could produce some or all of the changes of puberty.

Harder to detect as an influence on puberty are the more diffusely distributed environmental chemicals like PCBs (polychlorinated biphenyl), which can bind and trigger estrogen receptors.

More obvious degrees of partial puberty from direct exposure of young children to small but significant amounts of pharmaceutical sex steroids from exposure at home may be detected during medical evaluation for precocious puberty, but mild effects and the other potential exposures outlined above would not.

Bisphenol A (BPA) is a chemical used to make plastics, and is frequently used to make baby bottles, water bottles, sports equipment, medical devices, and as a coating in food and beverage cans. Scientists are concerned about BPA's behavioral effects on fetuses, infants, and children at current exposure levels because it can effect the prostate gland, mammary gland, and lead to early puberty in girls. BPA mimics and interferes with the action of estrogen-an important reproduction and development regulator. 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. The highest estimated daily intakes of BPA occur in infants and children. Many plastic baby bottles contain BPA, and BPA is more likely to leach out of plastic when its temperature is increased, as when one warms a baby bottle or warms up food in the microwave.[46]

Nutritional influence

Nutritional factors are the strongest and most obvious environmental factors affecting timing of puberty.[39] Girls are especially sensitive to nutritional regulation because they must contribute all of the nutritional support to a growing fetus. Surplus calories (beyond growth and activity requirements) are reflected in the amount of body fat, which signals to the brain the availability of resources for initiation of puberty and fertility.

Much evidence suggests that for most of the last few centuries, nutritional differences accounted for majority of variation of pubertal timing in different populations, and even among social classes in the same population. Recent worldwide increased consumption of animal protein, other changes in nutrition, and increases in childhood obesity have resulted in falling ages of puberty, mainly in those populations with the higher previous ages. In many populations the amount of variation attributable to nutrition is shrinking.

Although available dietary energy (simple calories) is the most important dietary influence on timing of puberty, quality of the diet plays a role as well. Lower protein intakes and higher dietary fiber intakes, as occur with typical vegetarian diets, are associated with later onset and slower progression of female puberty.

Obesity influence and exercise

Scientific researchers have linked early obesity with a drop of puberty onset in girls. They have cited obesity as a cause of breast development before nine years and menarche before twelve years.[47] Early puberty in girls can be a harbinger of later health problems.[48]

The average level of daily physical activity has also been shown to affect timing of puberty, especially in females. A high level of exercise, whether for athletic or body image purposes, or for daily subsistence, reduces energy calories available for reproduction and slows puberty. The exercise effect is often amplified by a lower body fat mass and cholesterol.

Physical and mental illness

Chronic diseases can delay puberty in both boys and girls. Those that involve chronic inflammation or interfere with nutrition have the strongest effect. In the western world, inflammatory bowel disease and tuberculosis have been notorious for such an effect in the last century, while in areas of the underdeveloped world, chronic parasite infections are widespread.

Mental illnesses occur in puberty. The brain undergoes significant development by hormones which can contribute to mood disorders such as Major depressive disorder, bipolar disorder, dysthymia and schizophrenia. Girls aged between 15 and 19 make up 40% of anorexia nervosa cases.[49]

Stress and social factors

Some of the least understood environmental influences on timing of puberty are social and psychological. In comparison with the effects of genetics, nutrition, and general health, social influences are small, shifting timing by a few months rather than years. Mechanisms of these social effects are unknown, though a variety of physiological processes, including pheromones, have been suggested based on animal research.

The most important part of a child's psychosocial environment is the family, and most of the social influence research has investigated features of family structure and function in relation to earlier or later female puberty. Most of the studies have reported that menarche may occur a few months earlier in girls in high-stress households, whose fathers are absent during their early childhood, who have a stepfather in the home, who are subjected to prolonged sexual abuse in childhood, or who are adopted from a developing country at a young age. Conversely, menarche may be slightly later when a girl grows up in a large family with a biological father present.

More extreme degrees of environmental stress, such as wartime refugee status with threat to physical survival, have been found to be associated with delay of maturation, an effect that may be compounded by dietary inadequacy.

Most of these reported social effects are small and our understanding is incomplete. Most of these "effects" are statistical associations revealed by epidemiologic surveys. Statistical associations are not necessarily causal, and a variety of covariables and alternative explanations can be imagined. Effects of such small size can never be confirmed or refuted for any individual child. Furthermore, interpretations of the data are politically controversial because of the ease with which this type of research can be used for political advocacy. Accusations of bias based on political agenda sometimes accompany scientific criticism.

Another limitation of the social research is that nearly all of it has concerned girls, partly because female puberty requires greater physiologic resources and partly because it involves a unique event (menarche) that makes survey research into female puberty much simpler than male. More detail is provided in the menarche article.

Variations of sequence

The sequence of events of pubertal development can occasionally vary. For example, in about 15% of boys and girls, pubarche (the first pubic hairs) can precede, respectively, gonadarche and thelarche by a few months. Rarely, menarche can occur before other signs of puberty in a few girls. These variations deserve medical evaluation because they can occasionally signal a disease.

Conclusion

In a general sense, the conclusion of puberty is reproductive maturity. Criteria for defining the conclusion may differ for different purposes: attainment of the ability to reproduce, achievement of maximal adult height, maximal gonadal size, or adult sex hormone levels. Maximal adult height is achieved at an average age of 15 years for an average girl and 18 years for an average boy. Potential fertility (sometimes termed nubility) usually precedes completion of growth by 1–2 years in girls and 3–4 years in boys. Stage 5 typically represents maximal gonadal growth and adult hormone levels.

Neurohormonal process

The endocrine reproductive system consists of the hypothalamus, the pituitary, the gonads, and the adrenal glands, with input and regulation from many other body systems. True puberty is often termed "central puberty" because it begins as a process of the central nervous system. A simple description of hormonal puberty is as follows:

  1. The brain's hypothalamus begins to release pulses of GnRH.
  2. Cells in the anterior pituitary respond by secreting LH and FSH into the circulation.
  3. The ovaries or testes respond to the rising amounts of LH and FSH by growing and beginning to produce estradiol and testosterone.
  4. Rising levels of estradiol and testosterone produce the body changes of female and male puberty.

The onset of this neurohormonal process may precede the first visible body changes by 1–2 years.

Components of the endocrine reproductive system

The arcuate nucleus of the hypothalamus is the driver of the reproductive system. It has neurons which generate and release pulses of GnRH into the portal venous system of the pituitary gland. The arcuate nucleus is affected and controlled by neuronal input from other areas of the brain and hormonal input from the gonads, adipose tissue and a variety of other systems.

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.

The adrenal glands are a second source for steroid hormones. Adrenal maturation, termed adrenarche, typically precedes gonadarche in mid-childhood.

Major hormones

Endocrine perspective

The endocrine reproductive system becomes functional by the end of the first trimester of fetal life. The testes and ovaries become briefly inactive around the time of birth but resume hormonal activity until several months after birth, when incompletely understood mechanisms in the brain begin to suppress the activity of the arcuate nucleus. This has been referred to as maturation of the prepubertal "gonadostat," which becomes sensitive to negative feedback by sex steroids. The period of hormonal activity until several months after birth, followed by suppression of activity, may correspond to the period of infant sexuality, followed by a latency stage, which Sigmund Freud described.[51]

Gonadotropin and sex steroid levels fall to low levels (nearly undetectable by current clinical assays) for approximately another 8 to 10 years of childhood. Evidence is accumulating that the reproductive system is not totally inactive during the childhood years. Subtle increases in gonadotropin pulses occur, and ovarian follicles surrounding germ cells (future eggs) double in number.

Normal puberty is initiated in the hypothalamus, with de-inhibition of the pulse generator in the arcuate nucleus. This inhibition of the arcuate nucleus is an ongoing active suppression by other areas of the brain. The signal and mechanism releasing the arcuate nucleus from inhibition have been the subject of investigation for decades and remain incompletely understood. Leptin levels rise throughout childhood and play a part in allowing the arcuate nucleus to resume operation. If the childhood inhibition of the arcuate nucleus is interrupted prematurely by injury to the brain, it may resume pulsatile gonadotropin release and puberty will begin at an early age.

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. The LH pulses are the consequence of pulsatile GnRH secretion by the arcuate nucleus that, in turn, is the result of an oscillator or signal generator in the central nervous system ("GnRH pulse generator").[52] In the years preceding physical puberty, Robert M. Boyar discovered that the gonadotropin pulses occur only during sleep, but as puberty progresses they can be detected during the day.[53] By the end of puberty, there is little day-night difference in the amplitude and frequency of gonadotropin pulses.

Some investigators have attributed the onset of puberty to a resonance of oscillators in the brain.[54][55][56][57] By this mechanism, the gonadotropin pulses that occur primarily at night just before puberty represent beats.[58][59][60]

An array of "autoamplification processes" increases the production of all of the pubertal hormones of the hypothalamus, pituitary, and gonads[citation needed].

Regulation of adrenarche and its relationship to maturation of the hypothalamic-gonadal axis is not fully understood, and some evidence suggests it is a parallel but largely independent process coincident with or even preceding central puberty. Rising levels of adrenal androgens (termed adrenarche) can usually be detected between 6 and 11 years of age, even before the increasing gonadotropin pulses of hypothalamic puberty. Adrenal androgens contribute to the development of pubic hair (pubarche), adult body odor, and other androgenic changes in both sexes. The primary clinical significance of the distinction between adrenarche and gonadarche is that pubic hair and body odor changes by themselves do not prove that central puberty is underway for an individual child.

Hormonal changes in boys

Early stages of male hypothalamic maturation seem to be very similar to the early stages of female puberty, though occurring about 1–2 years later.

LH stimulates the Leydig cells of the testes to make testosterone and blood levels begin to rise. For much of puberty, nighttime levels of testosterone are higher than daytime. Regularity of frequency and amplitude of gonadotropin pulses seems to be less necessary for progression of male than female puberty.

However, a significant portion of testosterone in adolescent boys is converted to estradiol. Estradiol mediates the growth spurt, bone maturation, and epiphyseal closure in boys just as in girls. Estradiol also induces at least modest development of breast tissue (gynecomastia) in a large proportion of boys. Boys who develop mild gynecomastia or even developing swellings under nipples during puberty are told the effects are temporary in some male teenagers due to high levels of Estradiol.

Another hormonal change in males takes place during the teenage years for most young men. At this point in a males life the testosterone levels slowly rise, and most of the effects are mediated through the androgen receptors by way of conversion dihydrotestosterone in target organs (especially that of the bowels).

Hormonal changes in girls

As the amplitude of LH pulses increases, the theca cells of the ovaries begin to produce testosterone and smaller amounts of progesterone. Much of the testosterone moves into nearby cells called granulosa cells. Smaller increases of FSH induce an increase in the aromatase activity of these granulosa cells, which converts most of the testosterone to estradiol for secretion into the circulation.

Rising levels of estradiol produce the characteristic estrogenic body changes of female puberty: growth spurt, acceleration of bone maturation and closure, breast growth, increased fat composition, growth of the uterus, increased thickness of the endometrium and the vaginal mucosa, and widening of the lower pelvis.

As the estradiol levels gradually rise and the other autoamplification processes occur, a point of maturation is reached when the feedback sensitivity of the hypothalamic "gonadostat" becomes positive. This attainment of positive feedback is the hallmark of female sexual maturity, as it allows the mid cycle LH surge necessary for ovulation.

Levels of adrenal androgens and testosterone also increase during puberty, producing the typical androgenic changes of female puberty: pubic hair, other androgenic hair as outlined above, body odor, acne.

Growth hormone levels rise steadily throughout puberty. IGF1 levels rise and then decline as puberty ends. Growth finishes and adult height is attained as the estradiol levels complete closure of the epiphyses.

Stages

See also

References

  • Gordon, Catharine M.; Laufer, MR (2005). "Chapter 4: Physiology of puberty". in Emans SJH, Goldstein DP, Laufer, MR, eds.. Pediatric and Adolescent Gynecology (5th ed.). Philadelphia: Lippincott, Williams & Wilkins. pp. 120–155. ISBN 0781744938. 
  • Gungor, Neslihan; Arslanian SA (2002). "Chapter 21: Nutritional disorders: integration of energy metabolism and its disorders in childhood". in Sperling, MA ed.. Pediatric Endocrinology (2nd ed.). Philadelphia: Saunders. pp. 689–724. ISBN 0721695396. 
  • Marshall, William A.; Tanner, JM (1986). "Chapter 8: Puberty". in Falkner F, Tanner JM, eds.. Human Growth: A Comprehensive Treatise (2nd ed.). New York: Plenum Press. pp. 171–209. ISBN 0-306-41952-1. 
  • Rosenfield, Robert L. (2002). "Chapter 16: Female puberty and its disorders". in Sperling, MA ed.. Pediatric Endocrinology (2nd ed.). Philadelphia: Saunders. pp. 455–518. ISBN 0721695396. 
  • Styne, Dennis M. (2002). "Chapter 18: The testes: disorders of sexual differentiation and puberty in the male". in Sperling, MA ed.. Pediatric Endocrinology (2nd ed.). Philadelphia: Saunders. pp. 565–628. ISBN 0721695396. 
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  9. ^ Essential Reproduction, M Johnson, Blackwell Publishers, 6Rev Ed edition (29 Jun 2007)
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  11. ^ Meister, B; Håkansson, ML (2001). "Leptin receptors in hypothalamus and circumventricular organs.". Clinical and experimental pharmacology & physiology 28 (7): 610–617. doi:10.1046/j.1440-1681.2001.03493.x. PMID 11458889. 
  12. ^ Clayton, PE; Trueman, JA (2000). "Leptin and puberty.". Archives of disease in childhood 83 (1): 1–4. doi:10.1136/adc.83.1.1. PMID 10868988. 
  13. ^ Topaloglu, AK; Reiman, F; Guclu, M; Yalin, AS; Kotan, LD; Porter, KM; Serin, A; Mungan, NO et al. (2009). "TAC3 and TACR3 mutations in familial hypogonadotropic hypogonadism reveal a key role for Neurokinin B in the central control of reproduction.". Nature genetics 41 (3): 354–358. doi:10.1038/ng.306. PMID 19079066. 
  14. ^ Styne (2002), p. 598
  15. ^ Jones, Kenneth W. (2006). Smith's Recognizable Patterns of Human Malformation. St. Louis, Mo: Elsevier Saunders. ISBN 0-7216-0615-6. 
  16. ^ Marshall (1986), p. 180.
  17. ^ "Puberty -- Changes for Males". pamf.org. http://www.pamf.org/teen/health/puberty/physicalchanges.html. Retrieved 2009-02-20. 
  18. ^ a b c "Getting The Facts: Puberty". ppwr. http://www.ppwr.on.ca/03_07.html. Retrieved 2009-02-20. 
  19. ^ "The No-Hair Scare". PBS. http://pbskids.org/itsmylife/body/puberty/article7.html. Retrieved 2009-02-20. 
  20. ^ "The structure of the larynx". Encyclopædia Britannica. http://www.britannica.com/EBchecked/topic/559032/speech/68966/The-structure-of-the-larynx. Retrieved 2009-02-20. 
  21. ^ a b Marshall (1986), p. 187
  22. ^ a b c Marshall (1986), p. 188
  23. ^ a b c d Tanner, JM; Davies, PS (1985). "Clinical longitudinal standards for height and height velocity for North American children.". The Journal of pediatrics 107 (3): 317–329. doi:10.1016/S0022-3476(85)80501-1. PMID 3875704. 
  24. ^ Gordon (2005), p. 151
  25. ^ Marshall (1986), p. 186–7
  26. ^ Rosenfield (2002), p. 462
  27. ^ Siegel, MJ; Surratt, JT (1992). "Pediatric gynecologic imaging.". Obstetrics and gynecology clinics of North America 19 (1): 103–127. PMID 1584537. 
  28. ^ a b Apter, D (1980). "Serum steroids and pituitary hormones in female puberty: a partly longitudinal study.". Clinical endocrinology 12 (2): 107–120. doi:10.1111/j.1365-2265.1980.tb02125.x. PMID 6249519. 
  29. ^ Marshall (1986), p. 196-7
  30. ^ Southam, AL; Richart, RM (1966). "The prognosis for adolescents with menstrual abnormalities.". American journal of obstetrics and gynecology 94 (5): 637–645. PMID 5906589. 
  31. ^ Hips widen during female puberty http://www.columbia.edu/itc/hs/pubhealth/modules/reproductiveHealth/anatomy.html coulmbia.edu
  32. ^ Gungor (2002), pages 699-700
  33. ^ a b Rosenfield (2002)
  34. ^ Nelson RJ. 2005. Introduction to Behavioral Endocrinology. Sinauer Associates: Massachusetts. p357.
  35. ^ National Research Center for Women and Families (2001). "When Little Girls Become Women: Early Onset of Puberty in Girls". http://www.center4research.org/children11.html. Retrieved 2009-07-22. 
  36. ^ Finley, Harry. "Average age at menarche in various cultures". Museum of Menstruation and Women's Health. http://www.mum.org/menarage.htm. Retrieved 2007-08-02. 
  37. ^ Whincup, PH; Gilg, JA; Odoki, K; Taylor, SJ; Cook, DG (2001). "Age of menarche in contemporary British teenagers: survey of girls born between 1982 and 1986.". BMJ(Clinical research ed.) 322 (7294): 1095–1096. doi:10.1136/bmj.322.7294.1095. PMID 11337438. 
  38. ^ "Girls maturing slightly earlier". BBC News. 2001-05-03. http://news.bbc.co.uk/1/hi/health/1310280.stm. Retrieved 2007-08-02. 
  39. ^ a b c . doi:10.1111/j.1532-7795.2007.00546.x (inactive 2009-10-08). 
  40. ^ Mustanski, BS; Viken, RJ; Kaprio, J; Pulkkinen, L; Rose, RJ (2004). "Genetic and environmental influences on pubertal development: longitudinal data from Finnish twins at ages 11 and 14.". Developmental psychology 40 (6): 1188–1198. doi:10.1037/0012-1649.40.6.1188. PMID 15535766. 
  41. ^ Treloar, SA; Martin, NG (1990). "Age at menarche as a fitness trait: nonadditive genetic variance detected in a large twin sample.". American journal of human genetics 47 (1): 137–148. PMID 2349942. 
  42. ^ Kaprio, J; Rimpelä, A; Winter, T; Viken, RJ; Rimpelä, M; Rose, RJ (1995). "Common genetic influences on BMI and age at menarche.". Human biology; an international record of research 67 (5): 739–753. PMID 8543288. 
  43. ^ Comings, DE; Muhleman, D; Johnson, JP; MacMurray, JP (2002). "Parent-daughter transmission of the androgen receptor gene as an explanation of the effect of father absence on age of menarche.". Child development 73 (4): 1046–1051. doi:10.1111/1467-8624.00456. PMID 12146732. 
  44. ^ Diana Zuckerman, "When Little Girls Become Women: Early Onset of Puberty in Girls" (This article appeared in The Ribbon, a newsletter of the Cornell University Program on Breast Cancer and Environmental Risk Factors in New York States (BCERF), Vol 6, No. 1, Winter 2001.) http://www.center4research.org/children11.html
  45. ^ , T., Dumanoski, D. and Myers, J.P. Our Stolen Future, 1996, Plume: New York.
  46. ^ Are Bisphenol A (BPA) Plastic Products Safe for Infants and Children?
  47. ^ Phil McKenna, "Childhood obesity brings early puberty for girls" "New Scientist" March 5, 2007 http://www.newscientist.com/article/dn11307-childhood-obesity-brings-early-puberty-for-girls.html
  48. ^ Molly, M. Ginty, "US Girls' Early Puberty Attracts Research Flurry" "Women's eNews" http://www.womensenews.org/article.cfm/dyn/aid/3113
  49. ^ Bulik, CM; Reba, L; Siega-riz, AM; Reichborn-kjennerud, T (2005). "Anorexia nervosa: definition, epidemiology, and cycle of risk.". The International journal of eating disorders 37 Suppl: S2–9; discussion S20–1. doi:10.1002/eat.20107. PMID 15852310. 
  50. ^ Topaloglu, A Kemal; Reimann, Frank; Guclu, Metin; Yalin, Ayse Serap; Kotan, L Damla; Porter, Keith M; Serin, Ayse; Mungan, Neslihan O et al. (2008). "TAC3 and TACR3 mutations in familial hypogonadotropic hypogonadism reveal a key role for Neurokinin B in the central control of reproduction". Nature Genetics 41: 354. doi:10.1038/ng.306. Lay summary – e! Science News (2008-12-11). 
  51. ^ Lehrer, S (1984). "Modern correlates of Freudian psychology. Infant sexuality and the unconscious.". The American journal of medicine 77 (6): 977–80. PMID 6507468. http://sites.google.com/site/infantsexuality/. 
  52. ^ Neill, J. D. (2001). "In Memoriam: Ernst Knobil (1926-2000)". Endocrine Reviews 22: 721. doi:10.1210/er.22.6.721. 
  53. ^ Boyar, R; Finkelstein, J; Roffwarg, H; Kapen, S; Weitzman, E; Hellman, L (1972). "Synchronization of augmented luteinizing hormone secretion with sleep during puberty.". The New England journal of medicine 287 (12): 582–586. PMID 4341276. 
  54. ^ Sizonenko, PC; Aubert, ML (1986). "Neuroendocrine changes characteristic of sexual maturation.". Journal of neural transmission. Supplementum 21: 159–181. PMID 3462329. 
  55. ^ Rivest, RW (1991). "Sexual maturation in female rats: hereditary, developmental and environmental aspects.". Experientia 47 (10): 1027–1038. PMID 1936201. 
  56. ^ Yellon, SM; Newman, SW (1991). "A developmental study of the gonadotropin-releasing hormone neuronal system during sexual maturation in the male Djungarian hamster.". Biology of reproduction 45 (3): 440–446. PMID 1782292. 
  57. ^ Armstrong, SM; Redman, JR (1991). "Melatonin: a chronobiotic with anti-aging properties?". Medical hypotheses 34 (4): 300–309. PMID 1865836. 
  58. ^ Lehrer, S (1983). "Puberty and resonance: a hypothesis.". The Mount Sinai journal of medicine, New York 50 (1): 39–43. PMID 6601758. http://stevenlehrer.com/images/pubres.pdf. 
  59. ^ Lehrer, S (1986). "Rats on 22.5-hr light:dark cycles have vaginal opening earlier than rats on 26-hr light:dark cycles.". Journal of pineal research 3 (4): 375–378. PMID 3783418. 
  60. ^ Vilaplana, J; Madrid, JA; Sánchez-vázquez, J; Campuzano, A; Cambras, T; Díez-noguera, A (1995). "Influence of period length of light/dark cycles on the body weight and food intake of young rats.". Physiology & behavior 58 (1): 9–13. PMID 7667433. 

Further reading

  • Colburn, T., Dumanoski, D. and Myers, J.P. Our Stolen Future, 1996, Plume: New York.
  • Ducros, A. and Pasquet, P. "Evolution de l'âge d'apparition des premières règles (ménarche) en France". Biométrie Humaine (1978), 13, 35–43.
  • Herman-giddens, ME; Slora, EJ; Wasserman, RC; Bourdony, CJ; Bhapkar, MV; Koch, GG; Hasemeier, CM (1997). "Secondary sexual characteristics and menses in young girls seen in office practice: a study from the Pediatric Research in Office Settings network.". Pediatrics 99 (4): 505–12. doi:10.1542/peds.99.4.505. PMID 9093289.  Newer data suggesting that lower age thresholds for evaluation should be used.
  • Plant TM, Lee PA, eds. The Neurobiology of Puberty. Bristol: Society for Endocrinology, 1995. Proceedings of the latest (4th) International Conference on the Control of the Onset of Puberty, containing summaries of current theories of physiological control, as well as GnRH analog treatment.
  • Tanner, JM; Davies, PS (1985). "Clinical longitudinal standards for height and height velocity for North American children.". The Journal of pediatrics 107 (3): 317–29. doi:10.1016/S0022-3476(85)80501-1. PMID 3875704.  Highly useful growth charts with integrated standards for stages of puberty.
  • Sizonenko, PC. Role of sex steroids during development—integration. in Bourguignon, Jean Pierre & Tony M. Plant. The Onset of Puberty in Perspective: Proceedings of the 5th International Conference on the Control of the Onset of Puberty, Held in Liège, Belgium, 26–28 September 1999. Elsevier. Amsterdam & New York 2000. ISBN 0444502963. pp 299–306.

External links


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[[File:|thumb|Puberty is what happens to the bodies of girls and boys that changes them into adult women and men. When this happens, their bodies change in many ways.]]

Puberty (pronounced [ˈpjuːbəti], PEW-bə-ti (British); [ˈpjubərdi], PEW-ber-di (U.S.)) is what happens in children's bodies that changes them into adults. After puberty, people are able to make children. A young woman who has gone through puberty can become pregnant and have a baby. At puberty, a young man's body begins making sperm and he starts to be able to ejaculate, which is semen coming out from his penis when he is sexually excited. If he has sexual intercourse (sex) with a young woman, he can make her pregnant. Puberty is started by hormones, which are chemicals that tell parts of the body to do things. On average, girls start puberty between the ages of nine and 14 years, and boys start between 10 and 17 years. However, people all over the world start puberty at different ages. Changes that happen to young men and women during puberty include the sex organs growing bigger, hair appearing on the body, and growing taller and stronger. People often notice young men's voices getting deeper, and young women growing breasts and starting to menstruate (have periods).

Because puberty is the time in a child's life when he or she becomes able to make children, this is seen as very important. Therefore, people in many countries around the world have different ways of marking this event.

Contents

How the body controls puberty

[[File:|thumb|200px|The location of the pituitary gland is shown in red. The gland makes hormones that cause males' and females' bodies to start puberty.]]

Puberty is started and carried on by different hormones. Hormones are chemicals that tell parts of the body to do things. Hormones are made by glands in the body. Glands are organs (special parts) of the body that make hormones.

This is what happens during puberty:[1]

  1. A gland at the bottom of the brain called the hypothalamus sends gonadotropin-releasing hormone (GnRH) into a nearby gland called the pituitary gland.
  2. GnRH causes cells in the pituitary gland to make two hormones, luteinizing hormone (LH) and follicle stimulating hormone (FSH).[2] LH and FSH are types of hormones called gonadotropins. The bloodstream carries these hormones around the body.
  3. LH and FSH make the gonads grow larger and start producing their own hormones, estradiol and testosterone. A girl's gonads are her ovaries, and a boy's gonads are his testicles (also called testes). Both ovaries and testicles produce estradiol and testosterone, but ovaries produce more estradiol and testicles produce more testosterone. Estradiol and testosterone are types of hormones called steroid hormones. Steroid hormones are also made by the body's two adrenal glands, which sit on top of the two kidneys.
  4. When the amount of estradiol and testosterone in the body increases, various parts of the body change.

When puberty starts and ends

Puberty in boys and girls starts when their bodies start making a lot of gonadotropin-releasing hormone (GnRH).[2][3] Scientists do not know for sure what causes the body to do this. However, they have noticed that puberty begins when girls weigh about 47 kilograms (104 lb) and boys weigh about 55 kilograms (121 lb). This suggests that the body is told to make a lot of GnRH by a hormone called leptin, which is made by fat tissue.[4] People whose bodies have problems with leptin do not go through puberty.[5]

On average, girls start puberty between the ages of 9 and 14 years, and boys start between 10 and 17 years. However, just because a person's puberty does not start during these ages does not mean they are not normal.[6] People from all over the world start puberty at different ages. This is because of their environment (things around them), and maybe even events in their lives.[7] Here are some of the things that make puberty happen at different ages in people:

  • Genetics. Genetics is the study of how parents pass on to their children some of the way they are through their genes. Half of a person's genes come from the mother. The other half come from the father. Some studies have found that mothers and daughters tend to start puberty at about the same age.[8][9]
  • Diet. Boys and girls who have a good diet – who eat healthy food – tend to start puberty earlier.[8] Today, people start puberty younger than in the 1840s. For example, in Norway, girls born in 1840 had their first period (see below) at an average age of 17 years; in France the average age was 15.3 years; and in England it was 16.5 years.[10] This may be because people have better food to eat today.
  • Exercise. Young people who exercise a lot, such as athletes and gymnasts, may start puberty later. It may also happen more slowly for them. This is thought to be because their bodies use up the food that they eat faster. This causes them to have less body fat, so there is less leptin to tell their brains to start puberty.
  • Obesity. Obesity is the state of being very overweight. A scientific study seems to say that girls who are obese start puberty early. Some obese girls have started growing breasts before the age of nine years and have had their first period before 12 years.[11] This could be because a woman who is pregnant needs more nutrients (chemicals the body needs to stay alive) to support her baby. Therefore, if a girl is obese, her body fat sends signals to her brain that she is ready to become pregnant. Girls who have early puberty can have health problems later on in life.[12]
  • Illness. Boys and girls who are sick for a long time, especially with illnesses that cause them to have a poor diet, tend to start puberty late. For example, this often happens to people who suffer from anorexia nervosa. Anorexia nervosa, often called "anorexia" for short, is an eating disorder. People with anorexia think that they are fat, or are very afraid of becoming fat. They try to lose weight by eating too little and doing too much exercise. To avoid gaining weight, they do not eat the amount of food their body needs. This causes them to stay at a weight that is not normal for their age and height.
  • Stress. It is thought that people who are under a lot of stress start puberty later. Some research seems to show that girls have their first period a bit later when their fathers are not around when they are young, when they have a stepfather, if they have been sexually abused for a long time, or if they were adopted by their parents from another country at a young age. On the other hand, the first period may happen a bit later when a girl grows up in a large family with her natural father around. However, scientists are not sure how correct these studies are. Not many studies have been done to find out if stress also causes boys to start puberty later.
  • Chemicals. Some scientists think people may start puberty earlier because their bodies are affected by chemicals such as estrogens and progestagens that are put in the environment by humans. Another chemical that may cause early puberty is Bisphenol A (BPA). It is used to make plastics, such as some types of baby bottles, water bottles and sports equipment.[13]

Girls usually reach their adult height and become sexually mature (able to have babies) about four years after puberty starts. Boys grow for about six years after puberty starts. Puberty in boys starts off more slowly than in girls, but then speeds up later on. Although boys are usually about 2 centimetres (0.8 in) shorter than girls before puberty begins, adult men on average end up about 13 centimetres (5.1 in) taller than women.[14]

Body changes in males

For most boys, puberty takes about six years and ends when they are about 17 or 18 years old. At the end of puberty, a teenager is usually about 10 to 30 centimetres (cm) (4 to 12 inches (in)) taller, 7 to 29 kilograms (kg) (15 to 65 pounds (lb)) heavier, and stronger. He is also able to make a woman pregnant (have a baby).[15]

Sex organs grow bigger

[[File:|thumb|upright|During puberty, a young man's penis and testicles grow bigger, and he starts ejaculating semen. Hair also begins to grow on his body.]]

The first sign of puberty in boys is that their testicles (also called the testes) and scrotum (the "bag" that the testicles are in) grow bigger.[16] Before puberty, each testicle is about 1.5 to 2 cm (0.6 to 0.8 in) long and has a volume of about 2 to 3 cubic centimetres (cc) (0.1 to 0.2 cubic inches (cu in)). About six years after puberty starts, the testicles reach their adult size.[17] The volume of an average adult man's testicle is about 18 to 20 cc (1.1 to 1.2 cu in). However, it is normal for some men to have testicles smaller than this size, and for other men to have larger testicles.[18]

The penis also grows bigger during puberty. At the start of puberty, the average length of the penis is 6 cm (2.4 in). The penis reaches adult size about five years later.[19] A study done in 1996 found the mean length of an adult man's penis is 3.5 in (8.9 cm) when it is flaccid (pronounced [ˈflæsɪd], FLA-sid) (not erect or hard).[20] The average length of an erect penis is about 12.9 to 15 cm (5.1 to 5.9 in).[20][21]

The testicles have two main jobs: to make hormones and sperm. The testicles make the hormone testosterone, which spreads around the body. This causes the changes in the body that make a boy grow into a man. Testosterone also makes a man feel like having sex. One year after puberty begins, when boys urinate (pee) after waking up in the morning, some sperm can be found in the urine. When a boy is about 13 years old his testicles will have grown to the stage that he may be fertile (able to make a woman pregnant). However, it will be still be difficult for him to do so. Boys usually only become fully fertile when they reach about 14 to 16 years of age. The sperm in the testicles mixes with other liquids in the body to form a whitish or yellowish and sticky fluid called semen. During puberty, two glands in the body called the seminal vesicles and prostate also grow bigger.[22] These glands make a lot of the liquid that is in semen.

When a man is sexually excited, he gets an erection – his penis becomes bigger, longer and harder. A male can become sexually excited if thinks about sex or sees a good-looking person, or if his penis rubs against something. During puberty, some boys also have spontaneous erections. These are erections that happen by themselves without any reason. This can be embarrassing when it happens in a public place.[23]

When a man's penis is sexually stimulated for some time, he has an orgasm and semen shoots out from the penis. This is called ejaculation. Young boys cannot ejaculate. A boy's first ejaculation usually happens about one year after he begins puberty. For some boys, the first ejaculation takes place when they are sleeping. This is called a nocturnal emission or a wet dream. It happens without the boy's control, often when he is having a dream about sex. Scientists believe that wet dreams are the body's way of removing too much semen. A study done of 5,300 white men in the United States in 1948[24] found that 13% of them had their first ejaculation through a wet dream,[25] This seems to tell us that most boys have their first ejaculation after masturbating. A male masturbates when he rubs his penis to make himself feel good sexually. The study also found that most boys who have their first ejaculation by masturbating do this a year or more earlier than boys who have their first ejaculation through a wet dream.[26] A 2004 survey by a magazine in Canada found that most males (43%) started masturbating when they were about 12 to 13 years old.[27] When a boy begins masturbating, wet dreams often stop happening because semen is taken out from his body regularly.

When a boy starts to ejaculate, he usually produces only a small amount of semen. The semen is different from what an adult man produces. It is usually clear and stays sticky. It either has no sperm in it, or sperm that do not move properly or do not move at all. A boy's semen only becomes like an adult man's semen about two years after his first ejaculation.[28]

Body hair and skin changes

[[File:|thumb|This picture shows how hair grows on a male body during and after puberty]]

File:Stubbly
During puberty, hair starts appearing on the face

Not long after a boy's testicles and penis start to grow, pubic hair (pronounced [ˈpjuːbik], PEW-bik) begins to appear. Pubic hair is hair that grows in the pubic region, which is the part of the body where the penis is. Pubic hair is shorter, curlier and rougher than hair on the head. It usually starts growing on the abdomen above the penis at the place where it joins the body. (The abdomen is the part of the torso where the navel or bellybutton is.) There may also be some hair on the scrotum. After about six months to a year, there will be a large triangle of hair in the pubic region. Within three to four years after puberty begins, there is a lot of pubic hair in the area above the penis. Later on, pubic hair also grows on the abdomen upwards towards the navel and on the insides of the thighs.[29]

About two years after pubic hair starts to appear,[29] hair also grows on other parts of the body:

  1. In the armpits.
  2. Around the anus.
  3. On the upper lip, forming a mustache (also spelled moustache in the United Kingdom and other countries).
  4. On the sides of the face in front of the ears, forming sideburns.
  5. Around the nipples.
  6. On the lower part of the face, forming a beard.

The hair on the arms, legs, chest, abdomen and back may also become thicker. Different men have different amounts of body hair. Many boys begin shaving when hair starts growing on their faces.

A larger amount of male hormones in the body cause changes to perspiration (sweat). This gives it a more "adult" body odor or smell. The hormones also cause sebaceous glands in the skin to make more sebum, a type of oil that keeps the skin from getting too dry. Sebum and dead skin cells can mix with a type of germ called bacteria and block pores (tiny openings) in the skin. This causes a skin problem called acne. Most people get acne during puberty. When a person has acne, he gets swellings on his skin called blackheads, whiteheads and pimples. Blackheads and whiteheads are painless, but pimples can be red and painful. They usually form on the face but can also appear on the neck, shoulders, upper back and chest. Oil glands on scalp – the part of the head on which hair grows – also make a lot of sebum. This can cause dandruff, in which small white bits of skin fall from the scalp.[30]

Voice changes

During puberty, a boy's larynx or voicebox also grows larger. This makes the laryngeal prominence or Adam's apple – the lump that sticks out of the front of his neck – larger too. As the larynx grows the vocal chords become longer and thicker, so they vibrate (move back and forth) more slowly. This causes the voice to lower in pitch or tone and become deeper. When this happens, it is sometimes said that the boy's voice has "broken". However, it actually does not happen overnight but over some time. During this time, the voice may sound scratchy. On average, a boy's voice normally reaches its adult sound when he is around 15 years old.[31]

Body growth

Towards the end of puberty, boys go through a "growth spurt" which lasts for about two to three years. During this time, their body grows taller very quickly. When the growth spurt is at its fastest point, some people grow 10 cm (4 in) or more a year. This happens about two years after puberty starts, usually between the ages of 13 and 15. When a boy reaches the end of his growth spurt when he is about 18 years old, he will be at his adult height. His body will not grow much taller after that.[1][32] Because of their growth spurt, boys' muscles can feel sore. These "growing pains" can feel worse if boys are active and do a lot of exercise. They go away after a while. Boys grow more slowly than girls, but for a longer time. That is why most men are taller than women.[32]

In the male body, some of the hormone testosterone is changed into another hormone called estradiol. Estradiol sometimes causes boys to grow small breasts. This is called gynecomastia. Scientists think that about half of all boys have gynecomastia in one or both sides of the chest.[33] There can be some swelling and pain.[32] The growth usually disappears by the end of puberty. However, if the breast growth is very obvious (which may happen if the person is overweight) and is causing him a lot of worry, it can be removed by surgery.[33]

During the later part of puberty, boys also go through a "strength spurt" during which their muscles grow quickly. The strength spurt is fastest about a year after the fastest point of the growth spurt. By the end of puberty, adult males have heavier bones and more muscle than females. In an average adult man, muscle makes up 50% and fat 15% of his weight. On the other hand, 40% of an average adult woman's weight is made up of muscle while 27% is made up of fat. Because men have less body fat than women, their hips do not grow bigger. Some bones like those in the jaw and shoulders grow more in males than in females. That is why males have wider faces and shoulders but narrower hips.[34]

Body changes in females

The changes in a girl's body during puberty usually take place between the ages of eight and 18 years. Most girls will have finished puberty around the age of 15. They will have breasts and pubic hair, will menstruate (have a period) every month, and will be able to get pregnant. They will usually also have reached their full adult height.[35]

Breasts grow

[[File:|thumb|180px|The first sign of puberty that can be seen on the outside of a girl's body is usually the breasts starting to grow.]]

When the breasts start to grow, this is normally the first sign of puberty that can be seen on the outside of a girl's body. This usually happens when girls are about the age of 10.5 years. A lump that is a bit hard appears in each breast under the areola, which is the dark ring around the nipple. The lump in one breast may grow before the other one.[36] This is called breast budding.[37] Within six to 12 months, both breasts will have started growing. The swelling can be felt and seen outside the edges of the areolae. About one and a half to two years after the breasts first start growing, they are close to the shape and size of an adult woman's breasts. The nipple and areola may be on a smaller mound on each breast. This small mound usually goes away when each breast is fully grown.[38] Whether the breasts are small or large depends on how much fat there is in the body.[37][39]

Body hair and skin changes

File:Androgenic
The brown parts of the picture on the left show where hair grows on a woman's body. Thicker hair is shown by the dark brown parts, and thinner hair by the light brown parts. As you can see from the picture on the right, men generally have more body hair than women.

Between the ages of about eight and 14 (on average, at 11 or 12 years), pubic hair begins to grow along the labia (the "lips" of the vulva), usually a few months after the breasts start growing.[38][40] At first the hair is thin and straight instead of curly, and there is not much of it.[35][40] Within a year, the pubic hair becomes rough, dark and curly and grows in a triangle shape in the pubic region. About one year after pubic hair begins appearing, underarm hair also grows. The hair on the arms and legs also gets thicker, and some girls may have hair appearing on their upper lip and in front of their ears.[41]

Like boys, higher amounts of hormones in the body cause girls' perspiration (sweat) to change. This gives them a more adult body odor or smell. The hormones also cause the skin to produce more sebum (oil), which usually leads to acne.

Changes to the sex organs and menstruation

When girls are between eight and 11 years old, the two ovaries in their body begin to grow bigger.[35] Each ovary is egg-shaped, and is attached to the side wall of the pelvis. The pelvis is a large set of bones in the hips. The ovaries are organs that make female hormones. These hormones cause a girl to grow into a woman, and make her feel like a woman. The hormones also make it possible for females to become pregnant and have babies. Inside the ovaries are about 200,000 ova (egg cells).[42] For a baby to be formed, a woman's ovum and a man's sperm must come together. During puberty, the ova also grow bigger.[43]

Between the ages of nine and 15 years (on average, at 12 to 13 years), the vagina and uterus (womb) become bigger.[35][43] The uterus is the organ in which a baby grows. The vagina is a tube leading from the uterus to the outside of the body. The opening of the vagina is inside the vulva, in between the legs. A clear or whitish fluid may start to flow out of the vagina to keep it clean.[36] Then, about two years after the breasts start to grow,[44] when a girl is between ten and 16 years old (on average, at 13 to 14 years), hormones made by her ovaries cause the ovaries to release an ovum, which moves into the uterus. Usually, only one ovum is released at a time. The hormones also tell the uterus to get ready for a baby, in case the ovum meets a sperm and gets fertilized. The walls of the uterus become thicker with extra tissue. Inside the thick part of the uterus are blood vessels and other nutrients that a baby will need to grow. If an ovum in the uterus gets fertilized, it sticks to the wall of the uterus and starts to grow. However, if the ovum is not fertilized, it does not stick. The uterus then gets rid of the ovum and the extra tissue by releasing it from the body. The tissue and blood flows out of the uterus through the vagina. This is called menstruation or having a period. The bleeding normally lasts for about three to five days, though some girls may bleed for longer or have a bit of bleeding between periods.[45] The uterus then starts preparing for another ovum. For most girls, the time between their periods is about one month. For about two years after menstruation starts, the time between periods is not always the same.[46] Some girls may skip a month, or have two periods close to each other. It is also normal to have cramps (rather painful squeezing feelings) or to feel bloated (swollen up) in the abdomen during periods.[45] When many girls start having periods, they begin using sanitary napkins (also called sanitary pads) or tampons to soak up the blood and tissue. A sanitary napkin is a piece of material that is absorbent (able to take in liquids) which is worn between the vulva and underpants. A tampon is a stick of absorbent material that is placed inside the vagina.

In 2004, a survey by a Canadian magazine found that most females (25%) started masturbating when they were about 12 to 13 years old.[27]

Body growth

Because of more hormones in the body, girls start to have more fat in their breasts, abdomen, hips and thighs. At the age of ten years, the average girl has 6% more body fat than the average boy, but by the end of puberty the difference is nearly 50%.[47] The fat makes sure that a baby growing inside a pregnant woman will have enough nutrients. Also, the bones in the pelvis move further apart to make room for a larger uterus and ovaries, and so there is space for a baby to grow in the uterus and to pass out of the body when it is born. The extra fat and wider hip bones that girls have give them a curvier shape.[48]

Girls also experience a growth spurt during puberty. In the first year after puberty begins, they grow about 8 cm (3 in). They grow even faster the next year or so, then the growth slows down and almost stops when they start menstruating. After a girl's periods begin, she usually does not grow more than 5 cm (2 in) taller.[41]

Emotional changes in males and females

The large amounts of hormones in the bodies of boys and girls during puberty can also affect their emotions. Young people begin to be attracted by (drawn to) each other and thinking about what it is like to have sex. They are often worried about what other people think about them. They can also feel an urge to do things that are dangerous, such as taking drugs or too many alcoholic drinks, or smoking. They sometimes want more independence – more power to decide things for themselves – and can get angry when their parents do not allow them to do things. The brains of teenagers are still growing, and it may take a while before they are mature enough to know how to make good choices about their lives. Therefore, it may be helpful for them to follow the advice of adults they trust, even if it does not make much sense to them at the time.[49]

Culture

[[File:|thumb|upright|An Australian aboriginal photographed some time before 1911]]

Because puberty is the time in a child's life when he or she becomes able to make children, this is seen as very important. Therefore, people in many countries around the world have different ways of marking this event.

Males

  • Australia. Among some aboriginal tribes in Australia, when young men go through puberty, their penises are cut or pierced (something sharp is used to poke through the skin), or they may be circumcised. Circumcision is cutting off the foreskin of the penis (the piece of skin that covers the glans penis or head of the penis). Young men are also sent away from home to go on a long trip on foot called a walkabout. During this trip, they learn how to hunt animals and survive in the open.[50]
  • Philippines. In some Philippine tribes such as the Agta, a young man who reaches puberty is taught how to masturbate by an older man. The young man then masturbates at a ceremony in front of other people. The semen that comes out from his penis is collected in a piece of animal skin. Later on, the young man wears this animal skin when he has sex with his wife as it is believed that this will help him have children.

Females

File:Navajo
A young Navajo girl photographed around 1904
  • America. Among the Navajo (pronounced [ˈnævəˌhoʊ], NA-və-hoe), who are a Native American people, a young woman who has had her first period goes through a four-day ceremony called Kinaalda which shows that she has changed from being a girl to a woman. The young woman's mother combs her hair and ties it into a ponytail. The young woman's family then sings a prayer, after which she puts on a dress made of a rug and jewellery made of turquoise and seashells. The young woman then runs as fast as she can towards the east, and turns around and runs home. She usually does this once in the morning and once in the evening every day during the ceremony. On the first night, the young woman does not go to sleep but stays awake while more prayers are sung. During the ceremony, the young woman also stands straight or lies on the ground in front of her mother, and her mother passes her hands over the young woman's body to make sure that she grows up beautiful. On the last day of the ceremony, the young woman does a final run; her mother passes her hands over her body one last time; and the young woman gives alkaan, a large cake made of maize (corn) that she has made, to her whole tribe to eat.[51]
  • Brazil. Among the Urubu-Kaapor people of Brazil, South America, when a young woman has had her first period, she goes into a room in her home covered with palm leaves to spend time alone for a month. She only eats cooked white cassava flour and white tortoise meat. She sleeps in a hammock (a type of bed made of rope that is hung above the floor) as it is believed that some magic will escape if her feet touch the ground. On the seventh day of her time alone, the young woman's father cuts her hair very short. Her legs are scratched with the tooth of an agouti, which is an animal that looks like a guinea pig. Pieces of cloth are wrapped around the woman's forehead and abdomen (tummy), and large ants are put inside the cloth. After the woman has been bitten by the ants a few times, the cloth is removed. The Urubu-Kaapor people believe that the woman will learn how to be strong if she suffers some pain. After the young woman has finished spending a month alone in her room, she makes a meal and a special drink from cassava and gives it to her family and other people in her village. The young woman is now considered an adult, and can wear a necklace of feathers and a waistband with flowers. She also puts pink makeup made from plants on her face.[52]
  • Ghana. When young women of some tribes in Ghana, Africa, have had their first period, they spend two to three weeks away from their family and friends. The queen mother of the town or village where they live and other older women teach the young women about sex and birth control. The young women also learn how to relate to men so that they can have a good marriage. After this, the young women appear at an event attended by the chief and everybody in the town or village. Young men also come to choose women to marry.[53]

Notes

  1. 1.0 1.1 Steven Dowshen (reviewer) (April 2007). "Everything you wanted to know about puberty". TeensHealth, The Nemours Foundation's Center for Children's Health Media. http://kidshealth.org/teen/sexual_health/changing_body/puberty.html. Retrieved 29 November 2008. 
  2. 2.0 2.1 T.M. Plant (January 2001). "Leptin, Growth Hormone, and the Onset of Primate Puberty". J. Clin. Endocrinol. Metab. 86 (1): 458–460. http://www.ncbi.nlm.nih.gov/pubmed/11232044. 
  3. M. Johnson (2007). Essential Reproduction (6th ed. ed.). Malden, Mass.: Blackwell Publishers. ISBN 9781405118668. 
  4. B. Meister; M.L. Håkansson (July 2001). [Expression error: Unexpected < operator "Leptin Receptors in Hypothalamus and Circumventricular Organs"]. Clin. Exp. Pharmacol. Physiol. 28 (7): 610–617. doi:10.1046/j.1440-1681.2001.03493.x. 
  5. P.E. Clayton; J.A. Trueman (July 2000). "Leptin and Puberty". Arch. Dis. Child. 83 (1): 1–4. http://www.ncbi.nlm.nih.gov/pubmed/10868988. 
  6. William A. Marshall; J.M. Tanner (1986). Human Growth: A Comprehensive Treatise (2nd ed. ed.). New York, N.Y.: Plenum Press. pp. 176–179. ISBN 9780306419522. 
  7. A.J. Giannini; A.E. Slaby (1981). [Expression error: Unexpected < operator "A Speculation on Oranges, Puberty, Marriage Contracts and Frozen Food"]. M.D. 25 (5): 51–52. 
  8. 8.0 8.1 Xiaojia Ge; Misaki N. Natsuaki, Jenae M. Neiderhiser, David Reiss (2007). [Expression error: Unexpected < operator "Genetic and Environmental Influences on Pubertal Timing: Results From Two National Sibling Studies"]. Journal of Research on Adolescence 17 (4): 767–788. doi:10.1111/j.1532-7795.2007.00546.x. 
  9. S.A. Treloar; N.G. Martin (July 1990). "Age at Menarche as a Fitness Trait: Nonadditive Genetic Variance Detected in a Large Twin Sample". American Journal of Human Genetics 47 (1): 137–148. http://www.ncbi.nlm.nih.gov/pubmed/2349942.  J. Kaprio; A. Rimpelä, T. Winter, R.J. Viken, M. Rimpelä, R.J. Rose (October 1995). "Common Genetic Influences on BMI and Age at Menarche". Human Biology 67 (5): 739–753. http://www.ncbi.nlm.nih.gov/pubmed/8543288.  D.E. Comings; D. Muhleman, J.P. Johnson, J.P. MacMurray (2002). [Expression error: Unexpected < operator "Parent–Daughter Transmission of the Androgen Receptor Gene as an Explanation of the Effect of Father Absence on Age of Menarche"]. Child Development 73 (4): 1046–1051. doi:10.1111/1467-8624.00456.  B.S. Mustanski; R.J. Viken, J. Kaprio, L. Pulkkinen, R.J. Rose (November 2004). [Expression error: Unexpected < operator "Genetic and Environmental Influences on Pubertal Development: Longitudinal Data from Finnish Twins at Ages 11 and 14"]. Developmental Psychology 40 (6): 1188–1198. doi:10.1037/0012-1649.40.6.1188. 
  10. Harry Finley (2003). "Average Age at Menarche in Various Cultures". Museum of Menstruation and Women's Health. http://www.mum.org/menarage.htm. Retrieved 25 November 2008.  P.H. Whincup; J.A. Gilg, K. Odoki, S.J.C. Taylor, D.G. Cook (5 May 2001). [Expression error: Unexpected < operator "Age of Menarche in Contemporary British Teenagers: Survey of Girls Born between 1982 and 1986"]. British Medical Journal 322: 1095–1096. doi:10.1136/bmj.322.7294.1095.  "Girls maturing slightly earlier". BBC News. 3 May 2001. http://news.bbc.co.uk/1/hi/health/1310280.stm. 
  11. Phil McKenna (5 March 2007). "Childhood obesity brings early puberty for girls". New Scientist. http://www.newscientist.com/article/dn11307-childhood-obesity-brings-early-puberty-for-girls.html. Retrieved 26 November 2008. 
  12. Molly M. Ginty (30 March 2007). US girls' early puberty attracts research flurry. Women's eNews. http://www.womensenews.org/article.cfm/dyn/aid/3113. Retrieved 26 November 2008. 
  13. Diana Zuckerman; Paul Brown, Laura Walls (July 2008). "Are Bisphenol A (BPA) plastic products safe for infants and children?". National Research Center for Women & Families. http://www.center4research.org/BPA.html. Retrieved 26 November 2008. 
  14. V. Abbassi (1998). "Growth and Normal Puberty". Pediatrics 102 (2 pt 3): 507–511. http://www.ncbi.nlm.nih.gov/pubmed/9685454. 
  15. Ann Byers (2007). "How Do Boys' Bodies Change during Puberty?". Frequently Asked Questions about Puberty. New York, N.Y.: Rosen Publishing. pp. 16–25 at 16. ISBN 978-1-4042-0966-4. 
  16. Dennis M. Styne (2002). M.A. Sperling. ed. Pediatric Endocrinology (2nd ed. ed.). Philadelphia, Pa.: Saunders. p. 598. ISBN 9780721695396. 
  17. Kenneth W. Jones (2006). Smith's Recognizable Patterns of Human Malformation. St. Louis, Mo.: Elsevier Saunders. ISBN 9780721606156. 
  18. Marshall, Human Growth, p. 180.
  19. W.A. Schonfeld (1943). [Expression error: Unexpected < operator "Primary and Secondary Sexual Characteristics: Study of their Development in Males from Birth through Maturity, with Biometric Study of Penis and Testes"]. American Journal of Diseases of Children 65: 535. 
  20. 20.0 20.1 H. Wessells H; T.F. Lue; J.W. McAninch (1996). [Expression error: Unexpected < operator "Penile Length in the Flaccid and Erect States: Guidelines for Penile Augmentation"]. Journal of Urology 156 (3): 995–997. doi:10.1016/S0022-5347(01)65682-9. 
  21. See also J. Chen; A. Gefen; A. Greenstein; H. Matzkin; D. Elad (2000). [Expression error: Unexpected < operator "Predicting Penile Size during Erection"]. International Journal of Impotence Research 12 (6): 328–333. doi:10.1038/sj.ijir.3900627.  "Ansell Research: The penis size survey". Ansell Healthcare. March 2001. http://www.free-condom-stuff.com/education/research.htm. Retrieved 29 November 2008. 
  22. Steve Dowshen (reviewer) (November 2007). "Male reproductive system". TeensHealth, The Nemours Foundation's Center for Children's Health Media. http://kidshealth.org/teen/sexual_health/changing_body/male_repro.html. Retrieved 29 November 2008. 
  23. Byers, Frequently Asked Questions about Puberty, p. 23.
  24. "Data from Alfred Kinsey's studies". The Kinsey Institute for Research in Sex, Gender, and Reproduction. http://www.kinseyinstitute.org/research/ak-data.html. Retrieved 30 November 2008. 
  25. Alfred C[harles] Kinsey; Wardell Baxter Pomeroy; Clyde Eugene Martin (1948). Sexual Behavior in the Human Male. Philadelphia, Pa.: W.B. Saunders Co.. p. 190. OCLC 25335222. 
  26. Kinsey, Sexual Behavior in the Human Male, p. 299.
  27. 27.0 27.1 Alice Klein (2004). "Love & Sex Guide". Now. http://www.nowtoronto.com/minisites/loveandsex/2004/s_survey_results.php. Retrieved 2 May 2010. 
  28. Z. Janczewski; L. Bablok (1985). "Semen Characteristics in Pubertal Boys: I. Semen Quality after First Ejaculation". Archives of Andrology 15: 199–205. http://www.ncbi.nlm.nih.gov/pubmed/3833078. 
  29. 29.0 29.1 Byers, Frequently Asked Questions about Puberty, p. 18.
  30. Byers, Frequently Asked Questions about Puberty, pp. 22–23.
  31. Byers, Frequently Asked Questions about Puberty, pp. 21–22.
  32. 32.0 32.1 32.2 Byers, Frequently Asked Questions about Puberty, p. 19.
  33. 33.0 33.1 Steven Dowshen (reviewer) (January 2007). "I'm a guy... so how come I'm developing breasts?". TeensHealth, The Nemours Foundation's Center for Children's Health Media. http://kidshealth.org/teen/sexual_health/guys/boybrst.html. Retrieved 2 December 2008. 
  34. Byers, Frequently Asked Questions about Puberty, p. 21.
  35. 35.0 35.1 35.2 35.3 J. Jeff Malta. "Five stages of puberty – girls?". Puberty 101. http://www.puberty101.com/p_pubgirls.shtml. Retrieved 1 December 2008. 
  36. 36.0 36.1 Marshall, Human Growth, p. 187.
  37. 37.0 37.1 Anne Byers (2007). "How do Girls' Bodies Change during Puberty?". Frequently Asked Questions about Puberty. New York, N.Y.: Rosen Publishing. pp. 26–33 at 27. ISBN 978-1-4042-0966-4. .
  38. 38.0 38.1 Marshall, Human Growth, p. 188.
  39. See also "Normal breast development". 007 Breasts. http://www.007b.com/breast_development.php. Retrieved 2 May 2010. 
  40. 40.0 40.1 J.M. Tanner; P.S. Davies (September 1985). "Clinical Longitudinal Standards for Weight and Height Velocity for North American Children". Journal of Pediatrics 107 (3): 317–329. http://www.ncbi.nlm.nih.gov/pubmed/3875704. 
  41. 41.0 41.1 Byers, Frequently Asked Questions about Puberty, p. 28.
  42. Byers, Frequently Asked Questions about Puberty, p. 31.
  43. 43.0 43.1 Marshall, Human Growth, pp. 186–187.
  44. J.M. Tanner; P.S. Davies (September 1985). "Clinical Longitudinal Standards for Height and Height Velocity for North American Children". Journal of Pediatrics 107 (3): 317–329. http://www.ncbi.nlm.nih.gov/pubmed/3875704. 
  45. 45.0 45.1 Byers, Frequently Asked Questions about Puberty, p. 32.
  46. D. Apter (1980). [Expression error: Unexpected < operator "Serum Steroids and Pituitary Hormones in Female Puberty: A Partly Longitudinal Study"]. Clinical Endocrinology (Oxford) 12 (2): 107–120. doi:10.1111/j.1365-2265.1980.tb02125.x. 
  47. Neslihan Gungor; S.A. Arslanian (2002). "Nutritional Disorders: Integration of Energy Metabolism and its Disorders in Childhood". In M.A. Sperling (ed.). Pediatric Endocrinology (2nd ed.). Philadelphia, Pa.: Saunders. pp. 689–724 at 699–700. ISBN 9780721695396. 
  48. Byers, Frequently Asked Questions about Puberty, p. 29.
  49. Byers, Frequently Asked Questions about Puberty, pp. 35–43.
  50. Tom Scheve. "Puberty rites around the world". How Stuff Works. http://health.howstuffworks.com/male-puberty7.htm. Retrieved 2 May 2010. 
  51. L.K. Smith (29 December 2006). "Native American Culture Perspectives – Kinaalda: The Navajo Puberty Ritual". Associated Content. http://www.associatedcontent.com/article/106033/native_american_culture_perspectives.html. Retrieved 2 May 2010. 
  52. Kiyoko Kakumasu. "Urubu-Kaapor Girls' Puberty Rites" (PDF). Summer Institute of Linguistics, Brazil. http://www.sil.org/americas/brasil/PUBLCNS/ANTHRO/ukpubert.pdf. Retrieved 2 May 2010. 
  53. David Osei-Adu. "Puberty rites". GhanaWeb. http://www.ghanaweb.com/GhanaHomePage/tribes/puberty_rites.php. Retrieved 2 May 2010.  Christine Opping (1973). "Notes on Cultural Aspects of Menstruation in Ghana" (PDF). http://archive.lib.msu.edu/DMC/African%20Journals/pdfs/Institue%20of%20African%20Studies%20Research%20Review/1973v9n2/asrv009002005.pdf. 

References

  • Byers, Ann (2007). Frequently Asked Questions about Puberty. New York, N.Y.: Rosen Publishing. ISBN 978-1-4042-0966-4. 
  • Marshall, William A.; J.M. Tanner (1986). Human Growth: A Comprehensive Treatise (2nd ed. ed.). New York, N.Y.: Plenum Press. ISBN 978-0-306-41952-2. 

Further reading

Articles

  • Chen, Chuansheng; Farruggia, Susan (2002). "Culture and Adolescent Development [Unit 11, Chapter 2]". Online Readings in Psychology and Culture. Ed. W.J. Lonner [et al.]. Bellingham, Wash.: Center for Cross-Cultural Research, Western Washington University. 
  • Fass, Paula S. (2004). "Puberty". Encyclopedia of Children and Childhood: In History and Society. Farmington Hills, Mich.: Thomson Gale. 

Books

  • Bailey, Jacqui; McCafferty, Jan (2004). Sex, Puberty, and All That Stuff: A Guide to Growing Up. Hauppage, N.Y.: Barron's. ISBN 978-1-435-26998-9. 
  • Bell, Ruth. Changing Bodies, Changing Lives: A Book for Teens on Sex and Relationships. New York, N.Y.: Three Rivers Press, 1998. ISBN 978-1-435-27659-8. 
  • Blackstone, Margaret; Guest, Elissa Haden (2006). Girl Stuff: A Survival Guide to Growing Up. Orlando, Fla.: Harcourt. ISBN 978-0-152-05679-7. 
  • Crump, Marguerite (2002). Don't Sweat It! Everybody's Answers to Questions You Don't Want to Ask: A Guide for Young People. Minneapolis, Minn.: Free Spirit. ISBN 978-1-575-42114-8. 
  • Gravelle, Karen; Castro, Nick; Castro, Chava (1998). What's Going On Down There? Answers to Questions Boys Find Hard to Ask. New York, N.Y.: Walker and Company. ISBN 978-0-802-78671-5, ISBN 978-0-802-77540-5, ISBN 978-0-613-75331-9. 
  • Harris, Robie H. (2009). It's Perfectly Normal: Changing Bodies, Growing Up, Sex & Sexual Health. Somerville, Mass.: Candlewick Press. ISBN 978-0-763-64483-3. 
  • Madaras, Lynda; Madaras, Area (2007). The "What's Happening to My Body?" Book for Boys. New York, N.Y.: Newmarket Press. ISBN 978-1-557-04769-4, ISBN 978-1-557-04765-6. 
  • Madaras, Lynda; Madaras, Area (2007). The "What's Happening to My Body?" Book for Girls. New York, N.Y.: Newmarket Press. ISBN 978-1-557-04768-7, ISBN 978-1-557-04764-9. 

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