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| Differences between male and female puberty | |
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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 or 11; boys at age 12 or 13.[8][9] Girls usually complete puberty by ages 15–17,[9][10][11] while boys usually complete puberty by ages 16–18.[9][10][12] Any increase in height beyond the post-pubertal age is uncommon. Girls attain reproductive maturity about 4 years after the first physical changes of puberty appear.[11] In contrast, boys accelerate more slowly but continue to grow for about 6 years after the first visible pubertal changes.[13]
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
For boys, an androgen called testosterone is the principal sex hormone. While testosterone produces all boys' 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.[14]
The hormone that dominates female development is an estrogen called estradiol. While estradiol promotes growth of breasts and uterus, it is also the principal hormone driving the pubertal growth spurt and epiphyseal maturation and closure.[15] Estradiol levels rise earlier and reach higher levels in women than in men.
Tags:Child,Adult,Breasts,Sex Steroids,Androgen,Testosterone,Sex Hormone,Virilization,Estrogen,Estradiol,Uterus,Epiphyseal,Lh,Fsh,Boy, | |
| Puberty onset | |
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The onset of puberty is associated with high GnRH pulsing, which precedes the rise in sex hormones, LH and FSH.[16] Exogenous GnRH pulses cause the onset of puberty.[17] Brain tumors which increase GnRH output may also lead to premature puberty.[18]
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.[19] Individuals who are deficient in leptin fail to initiate puberty.[20] 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[21] 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.
Tags:Brain,Gnrh,Leptin,Kisspeptin,Hormones, | |
| Physical changes in boys | |
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This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2009)
See also: Tanner scale
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| Testicular size, function, and fertility | |
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In boys, testicular enlargement is the first physical manifestation of puberty (and is termed gonadarche).[22] 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.[23] While 18–20 cm3 is an average adult size, there is wide variation in testicular size in the normal population.[24]
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].
During puberty, a male's scrotum will become larger and begin to dangle or hang below the body as opposed to being up tight. This is to accommodate the testicles to hang lower whereby the testicles need a certain temperature to be fertile and produce sperm. This is more commonly known as "balls dropping".
Tags:Body,Testes,Penis,Gonadarche,Sperm,Leydig Cells,Sertoli,Glans, | |
| Morning wood and random or unwanted erections | |
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Erections during sleep or when waking up are medically known as nocturnal penile tumescence and more commonly known as morning wood.[25] The penis can regularly get erect during sleep and men or boys often wake-up with an erection.[26] Once a boy reaches his teenage years, erections occur much more frequently due to puberty.[27] Erections can occur spontaneously at any time of day, and if clothed may cause a bulge or "hump". This can be disguised or hidden by wearing close-fitting underwear, a long shirt and baggier clothes.[28] Male erections are common for children and infants, and can even occur before birth.[29] Spontaneous erections are also known as involuntary or unwanted erections and are normal. Such erections can be embarrassing if they happen in public, such as a classroom or living room.[30][31]
Tags:Erections,Nocturnal Penile Tumescence,Embarrassing,Classroom,Living Room, | |
| Foreskin retraction | |
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During puberty, if not before, the tip and opening of a boy'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. The membrane that bonds the inner surface of the foreskin with the glans disintegrates and releases the foreskin to separate from the glans. The foreskin then gradually becomes retractable.[32]
Research in 1968 by Danish pediatrician Jakob Øster found that with the onset and continuation of puberty, the proportion of boys able to pull back their foreskins increased. At ages 12–13, Øster found that only 60% of boys were able to retract their foreskins; this increased to 85% at ages 14–15, and 95% by 16–17 years old. He also found that only 1% of those unable to fully retract suffered from phimosis at ages 14–17, the remainder were partially able to.[33] The findings were supported by further research by Japanese doctor Hiroyuki Kayaba et al in 1996, on a sample of over 600 boys,[34] and in 2004 Ishikawa and Kawakita found that by age 15, 77% of their sample of boys could retract their foreskins.[35]
Once a boy is able to retract his foreskin, penile hygiene should become an important feature of his routine body care. Although the American Academy of Pediatrics states there is "little evidence to affirm the association between circumcision status and optimal penile hygiene",[36] various studies suggest that uncircumcised boys are educated about the role of hygiene, including retracting the foreskin while urinating and rinsing underneath it and around the glans at each bathing opportunity. Regular washing under the foreskin was found, in a 1986 study by Krueger and Osborn, to reduce the risk of numerous penile disorders.[37]
Tags:Skin,Foreskin,Phimosis,American Academy Of Pediatrics, | |
| Pubic hair | |
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Pubic hair often appears on a boy shortly after the genitalia begin to grow. 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 the spread of pubic hair to the thighs and upward towards the navel as part of the developing abdominal hair.
Tags:Hair,Genitalia,Pubic Hair,Thighs,Navel,Abdominal Hair, | |
| Body and facial hair | |
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Facial hair of a male.
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.[9] 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 racial groups.[8] Facial hair is often present in late adolescence, but may not appear until significantly later.[38][39] Facial hair will continue to get coarser, darker and thicker for another 2–4 years after puberty.[38] Some men do not develop full facial hair for up to 10 years after the completion of puberty.[38] Chest hair may appear during puberty or years after.[8] Not all men have chest hair.
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| Voice change and Adam's apple | |
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"Squeaky-voiced teen" redirects here. For the fictional character, see Squeaky-Voiced Teen (The Simpsons).
Main article: Voice break
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.[40] 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.
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| Male musculature and body shape | |
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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 boys are 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.
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| Body odor and acne | |
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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.
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| Breast development | |
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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.[41] 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.[42]
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| Pubic hair | |
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Pubic hair is often the second noticeable change in puberty, usually within a few months of thelarche.[43] 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.[42] 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.[43]
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| Vagina, uterus, ovaries | |
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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).[44] Whitish secretions (physiologic leukorrhea) are a normal effect of estrogen as well.[41] In the two years following thelarche, the uterus, ovaries, and the follicles in the ovaries increase in size.[45] The ovaries usually contain small follicular cysts visible by ultrasound.[46][47]
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| Menstruation and fertility | |
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The first menstrual bleeding is referred to as menarche, and typically occurs about two years after thelarche.[43] The average age of menarche is 12.5 in the United States.[3] Most American girls experience their first period at 11, 12 or 13, but some experience it earlier than their 11th birthday and others after their 14th birthday. In fact, anytime between 8 and 16 is normal. In Canada, the average age of menarche is 12.72,[4] and in the United Kingdom it is 12.9.[5] The time between menstrual periods (menses) is not always regular in the first two years after menarche.[48] Ovulation is necessary for fertility, but may or may not accompany the earliest menses.[49] 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.[48] 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.[50] Nubility is used to designate achievement of fertility.
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| Body shape, fat distribution, and body composition | |
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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).[42][51] 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.[52]
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| Body odor and acne | |
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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.[53] Acne varies greatly in its severity.[53]
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| Variations | |
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This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2008)
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| Timing of the onset of puberty | |
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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.). A common definition for the onset of puberty is physical changes to a person's body.[54] These physical changes are the first visible signs of neural, hormonal, and gonadal function changes.
The age at which puberty begins varies between individuals; usually, puberty begins between 10 and 13 years of age. The age at which puberty begins is affected by both genetic factors and by environmental factors such as nutritional state and social circumstances.[8][55] 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.[56]
The average age at which puberty begins may be affected by race as well. For example, the average age of menarche in various populations surveyed has ranged from 12[3][4][5] 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.[57]
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| Historical shift | |
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The average age at which the onset of puberty occurs has dropped significantly since the 1840s.[58][59][60] This was dubbed 'the secular trend' by J.M. Tanner. 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.
A 2006 study in Denmark found that puberty, as evidenced by breast development, started at an average age of 9 years and 10 months, a year earlier than when a similar study was done in 1991. Scientists believe the phenomenon could be linked to obesity or exposure to chemicals in the food chain, and is putting girls at greater long-term risk of breast cancer.[61]
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| Genetic influence and environmental factors | |
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Various studies have found direct genetic effects to account for at least 46% of the variation of timing of puberty in well-nourished populations.[62][63][64][65] The genetic association of timing is strongest between mothers and daughters. The specific genes affecting timing are not yet known.[62] Among the candidates is an androgen receptor gene.[66]
Researchers[67] 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.
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| Hormones and steroids | |
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There is theoretical concern, and animal evidence, that environmental hormones and chemicals may affect aspects of prenatal or postnatal sexual development in humans.[68] 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 affect 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.[69]
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| Nutritional influence | |
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Nutritional factors are the strongest and most obvious environmental factors affecting timing of puberty.[62] 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 Tags: | |
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