Puberty
Encyclopedia
Puberty is the process of physical changes by which a child
's body
matures into an adult
body capable of reproduction, as initiated by hormonal
signals from the brain
to the gonad
s; the ovaries
in a girl, the testes in a boy. In response to the signals, the gonads produce hormones that stimulate the growth, function, and transformation of the brain
, bone
s, muscle
, blood
, skin
, hair
, breast
s, and sexual organs
. Physical growth
—height and weight—accelerates in the first half of puberty and is completed when the child has developed an adult body. Until the maturation of their reproductive capabilities, the pre-pubertal, physical differences between boys and girls are the genitalia, the penis
and the vagina
. Notable among the morphologic
changes in size, shape, composition, and functioning of the pubertal body, is the development of secondary sex characteristic
s, the “filling in” of the child’s body; from girl to woman, from boy to man. Derived from the Latin puberatum (age of maturity), the word puberty describes the physical changes to sexual maturation, not the psychosocial
and cultural maturation denoted by the term “adolescent development” in Western culture
, wherein adolescence
is the period of mental transition from childhood to adulthood
, which overlaps much of the body’s period of puberty.
s involved.
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. Girls usually complete puberty by ages 15–17, while boys usually complete puberty by ages 16–18. 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. In contrast, boys accelerate more slowly but continue to grow for about 6 years after the first visible pubertal changes.
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.
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. Estradiol levels rise earlier and reach higher levels in women than in men.
pulsing, which precedes the rise in sex hormones, LH
and FSH. Exogenous GnRH pulses cause the onset of puberty. Brain tumors which increase GnRH output may also lead to premature puberty.
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. Individuals who are deficient in leptin fail to initiate puberty. 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 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.
). 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. While 18–20 cm3 is an average adult size, there is wide variation in testicular size in the normal population.
The testes have two primary functions: to produce hormone
s and to produce sperm
. The Leydig cell
s 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 cell
s). Sperm can be detected in the morning urine of most boys after the first year of pubertal changes, and occasionally earlier. 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.
During puberty, a male's scrotum will become larger and begin to dangle or hang below the body as opposed to being up tight, to accommodate the production of sperm whereby the testicles need a certain temperature to be fertile.
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.
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. The findings were supported by further research by Japanese doctor Hiroyuki Kayaba et al in 1996, on a sample of over 600 boys, and in 2004 Ishikawa and Kawakita found that by age 15, 77% of their sample of boys could retract their foreskins.
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", 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.
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 thigh
s and upward towards the navel
as part of the developing abdominal hair
.
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. 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. Facial hair is often present in late adolescence, but may not appear until significantly later. Facial hair will continue to get coarser, darker and thicker for another 2–4 years after puberty. Some men do not develop full facial hair for up to 10 years after the completion of puberty. Chest hair may appear during puberty or years after. Not all men have chest hair.
, 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. 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. It usually precedes the development of significant facial hair by several months to years.
s 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.
of one or both breast
s, occurring on average at about 10.5 years of age. 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.
is often the second noticeable change in puberty, usually within a few months of thelarche. 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. 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 thigh
s and sometimes as abdominal hair
upward towards the navel
. In about 15% of girls, the earliest pubic hair appears before breast development begins.
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). Whitish secretions (physiologic leukorrhea
) are a normal effect of estrogen as well. In the two years following thelarche, the uterus
, ovaries
, and the follicles
in the ovaries increase in size. The ovaries usually contain small follicular cyst
s visible by ultrasound
.
is referred to as menarche
, and typically occurs about two years after thelarche
. The average age of menarche is 12.5 in the United States
. 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, and in the United Kingdom
it is 12.9. The time between menstrual periods (menses) is not always regular in the first two years after menarche.Ovulation
is necessary for fertility
, but may or may not accompany the earliest menses. 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. 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. Nubility is used to designate achievement of fertility.
and thus hips
widen (providing a larger birth canal). 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.
s 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. Acne varies greatly in its severity.
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. 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.
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 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.
, 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.
s affecting timing are not yet known. Among the candidates is an androgen receptor
gene.
Researchers 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.
s from pharmaceutical products are excreted into the sewage systems of large cities, and are sometimes detectable in the environment. Sex steroid
s 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 receptor
s 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.
al factors are the strongest and most obvious environmental factors affecting timing of puberty. Girls are especially sensitive to nutritional regulation because they must contribute all of the nutritional support to a growing fetus. Surplus calorie
s (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.
with an earlier onset of puberty in girls. They have cited obesity as a cause of breast development before nine years and menarche before twelve years. Early puberty in girls can be a harbinger of later health problems.
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.
and tuberculosis
have been notorious for such an effect in the last century, while in areas of the underdeveloped world, chronic parasite infection
s are widespread.
Mental illnesses occur in puberty. The brain undergoes significant development by hormone
s 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.
s, 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.
(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.
, the pituitary
, the gonad
s, and the adrenal gland
s, 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:
The onset of this neurohormonal process may precede the first visible body changes by 1–2 years.
of the hypothalamus
is the driver of the reproductive system. It has neuron
s 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 gonad
s, 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 gland
s are a second source for steroid hormones. Adrenal maturation, termed adrenarche
, typically precedes gonadarche in mid-childhood.
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 steroid
s. 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.
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 cell
s (future egg
s) 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"). 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. 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. By this mechanism, the gonadotropin pulses that occur primarily at night just before puberty represent beats
.
An array of "autoamplification processes" increases the production of all of the pubertal hormones of the hypothalamus, pituitary, and gonads.
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 androgen
s (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.
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 swelling
s under nipple
s 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).
. Much of the testosterone moves into nearby cells called granulosa cell
s. 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.
Child
Biologically, a child is generally a human between the stages of birth and puberty. Some vernacular definitions of a child include the fetus, as being an unborn child. The legal definition of "child" generally refers to a minor, otherwise known as a person younger than the age of majority...
's body
Body
With regard to living things, a body is the physical body of an individual. "Body" often is used in connection with appearance, health issues and death...
matures into an adult
Adult
An adult is a human being or living organism that is of relatively mature age, typically associated with sexual maturity and the attainment of reproductive age....
body capable of reproduction, as initiated by hormonal
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
signals from the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
to the gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s; the ovaries
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
in a girl, the testes in a boy. In response to the signals, the gonads produce hormones that stimulate the growth, function, and transformation of the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
, bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s, muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
, blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
, skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, hair
Human hair growth
Human hair grows everywhere on the body except for the soles of the feet, the lips, the palms of the hands, and the eyelids, apart from eyelashes...
, breast
Breast
The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
s, and sexual organs
Sex organ
A sex organ, or primary sexual characteristic, as narrowly defined, is any of the anatomical parts of the body which are involved in sexual reproduction and constitute the reproductive system in a complex organism; flowers are the reproductive organs of flowering plants, cones are the reproductive...
. Physical growth
Human development (biology)
Human development is the process of growing to maturity. In biological terms, this entails growth from a one-celled zygote to an adult human being.- Biological development:...
—height and weight—accelerates in the first half of puberty and is completed when the child has developed an adult body. Until the maturation of their reproductive capabilities, the pre-pubertal, physical differences between boys and girls are the genitalia, the penis
Penis
The penis is a biological feature of male animals including both vertebrates and invertebrates...
and the vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
. Notable among the morphologic
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
changes in size, shape, composition, and functioning of the pubertal body, is the development of secondary sex characteristic
Secondary sex characteristic
Secondary sex characteristics are features that distinguish the two sexes of a species, but that are not directly part of the reproductive system. They are believed to be the product of sexual selection for traits which give an individual an advantage over its rivals in courtship and aggressive...
s, the “filling in” of the child’s body; from girl to woman, from boy to man. Derived from the Latin puberatum (age of maturity), the word puberty describes the physical changes to sexual maturation, not the psychosocial
Psychosocial
For a concept to be psychosocial means it relates to one's psychological development in, and interaction with, a social environment. The individual needs not be fully aware of this relationship with his or her environment. It was first commonly used by psychologist Erik Erikson in his stages of...
and cultural maturation denoted by the term “adolescent development” in Western culture
Western culture
Western culture, sometimes equated with Western civilization or European civilization, refers to cultures of European origin and is used very broadly to refer to a heritage of social norms, ethical values, traditional customs, religious beliefs, political systems, and specific artifacts and...
, wherein adolescence
Adolescence
Adolescence is a transitional stage of physical and mental human development generally occurring between puberty and legal adulthood , but largely characterized as beginning and ending with the teenage stage...
is the period of mental transition from childhood to adulthood
Adult
An adult is a human being or living organism that is of relatively mature age, typically associated with sexual maturity and the attainment of reproductive age....
, which overlaps much of the body’s period of puberty.
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 steroidSex steroid
Sex steroids, also known as gonadal steroids, are steroid hormones that interact with vertebrate androgen or estrogen receptors. Their effects are mediated by slow genomic mechanisms through nuclear receptors as well as by fast nongenomic mechanisms through membrane-associated receptors and...
s involved.
For boys, an androgen
Androgen
Androgen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...
called testosterone
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
is the principal sex hormone. While testosterone produces all boys' changes characterized as virilization
Virilization
In biology and medicine, virilization refers to the biological development of sex differences, changes that make a male body different from a female body. Most of the changes of virilization are produced by androgens...
, 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.
The hormone that dominates female development is an estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
called estradiol
Estradiol
Estradiol is a sex hormone. Estradiol is abbreviated E2 as it has 2 hydroxyl groups in its molecular structure. Estrone has 1 and estriol has 3 . Estradiol is about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect...
. While estradiol promotes growth of breasts and uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
, it is also the principal hormone driving the pubertal growth spurt and epiphyseal maturation and closure. Estradiol levels rise earlier and reach higher levels in women than in men.
Puberty onset
The onset of puberty is associated with high GnRHGonadotropin-releasing hormone
Gonadotropin-releasing hormone , also known as Luteinizing-hormone-releasing hormone and luliberin, is a tropic peptide hormone responsible for the release of follicle-stimulating hormone and luteinizing hormone from the anterior pituitary. GnRH is synthesized and released from neurons within...
pulsing, which precedes the rise in sex hormones, LH
Luteinizing hormone
Luteinizing hormone is a hormone produced by the anterior pituitary gland. In females, an acute rise of LH called the LH surge triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone , it stimulates Leydig cell...
and FSH. Exogenous GnRH pulses cause the onset of puberty. Brain tumors which increase GnRH output may also lead to premature puberty.
The cause of the GnRH rise is unknown. Leptin
Leptin
Leptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...
might be the cause of the GnRH rise. Leptin has receptors in the hypothalamus which synthesizes GnRH. Individuals who are deficient in leptin fail to initiate puberty. 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 discovered that a mutation in genes encoding both Neurokinin B
Neurokinin B
Neurokinin B is a tachykinin peptide.It is found in higher concentration in pregnant women suffering pre-eclampsia and can bind the immune-cloaking molecule phosphocholine....
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
Kisspeptin
Kisspeptin , the product of the gene , is a G-protein coupled receptor ligand for GPR54. Kiss1 was originally identified as a human metastasis suppressor gene that has the ability to suppress melanoma and breast cancer metastasis...
, a compound responsible for triggering direct release of GnRH
Gonadotropin-releasing hormone
Gonadotropin-releasing hormone , also known as Luteinizing-hormone-releasing hormone and luliberin, is a tropic peptide hormone responsible for the release of follicle-stimulating hormone and luteinizing hormone from the anterior pituitary. GnRH is synthesized and released from neurons within...
as well as indirect release of LH
Luteinizing hormone
Luteinizing hormone is a hormone produced by the anterior pituitary gland. In females, an acute rise of LH called the LH surge triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone , it stimulates Leydig cell...
and FSH.
Testicular size, function, and fertility
In boys, testicular enlargement is the first physical manifestation of puberty (and is termed gonadarcheGonadarche
Gonadarche refers to the earliest gonadal changes of puberty. In response to pituitary gonadotropins, the ovaries in girls and the testes in boys begin to grow and increase the production of the sex steroids, especially estradiol and testosterone....
). 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. While 18–20 cm3 is an average adult size, there is wide variation in testicular size in the normal population.
The testes have two primary functions: to produce hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s and to produce sperm
Spermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...
. The Leydig cell
Leydig cell
Leydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone...
s produce testosterone
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
, which in turn produces most of the male pubertal changes. Most of the increasing bulk of testicular tissue is spermatogenic tissue (primarily Sertoli
Sertoli cell
A Sertoli cell is a 'nurse' cell of the testes that is part of a seminiferous tubule.It is activated by follicle-stimulating hormone and has FSH-receptor on its membranes.-Functions:...
and Leydig cell
Leydig cell
Leydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone...
s). Sperm can be detected in the morning urine of most boys after the first year of pubertal changes, and occasionally earlier. 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.
During puberty, a male's scrotum will become larger and begin to dangle or hang below the body as opposed to being up tight, to accommodate the production of sperm whereby the testicles need a certain temperature to be fertile.
Foreskin retraction
During puberty, if not before, the tip and opening of a boy's foreskinForeskin
In male human anatomy, the foreskin is a generally retractable double-layered fold of skin and mucous membrane that covers the glans penis and protects the urinary meatus when the penis is not erect...
becomes wider, progressively allowing for retraction down the shaft of the penis
Human penis
The human penis is an external sexual organ of male humans. It is a reproductive, intromittent organ that additionally serves as the urinal duct.-Parts:...
and behind the glans
Glans penis
The glans penis is the sensitive bulbous structure at the distal end of the penis. The glans penis is anatomically homologous to the clitoral glans of the female...
, 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.
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
Phimosis
Phimosis , from the Greek phimos ), is a condition where, in men, the foreskin cannot be fully retracted over the glans penis...
at ages 14–17, the remainder were partially able to. The findings were supported by further research by Japanese doctor Hiroyuki Kayaba et al in 1996, on a sample of over 600 boys, and in 2004 Ishikawa and Kawakita found that by age 15, 77% of their sample of boys could retract their foreskins.
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
American Academy of Pediatrics
The American Academy of Pediatrics is the major professional association of pediatricians in the United States. The AAP was founded in 1930 by 35 pediatricians to address pediatric healthcare standards. It currently has 60,000 members in primary care and sub-specialist areas...
states there is "little evidence to affirm the association between circumcision status and optimal penile hygiene", 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.
Pubic hair
Pubic hairPubic hair
Pubic hair is hair in the frontal genital area, the crotch, and sometimes at the top of the inside of the legs; these areas form the pubic region....
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 thigh
Thigh
In humans the thigh is the area between the pelvis and the knee. Anatomically, it is part of the lower limb.The single bone in the thigh is called the femur...
s and upward towards the navel
Navel
The navel is a scar on the abdomen caused when the umbilical cord is removed from a newborn baby...
as part of the developing abdominal hair
Abdominal hair
The term abdominal hair refers to the hair that grows on the abdomen of humans and non-human mammals, in the region between the pubic area and the thorax . The growth of abdominal hair follows the same pattern on nearly all mammals, vertically from the pubic area upwards and from the thorax...
.
Body and facial hair
Androgenic hair
Androgenic hair, colloquially body hair, is the terminal hair that develops on the body during and after puberty. It is differentiated from the head hair and less visible vellus hair, which are much finer and lighter in color. The growth of androgenic hair is related to the level of androgens in...
. The usual sequence is: underarm
Underarm
-Axillary intertrigo:Excessive perspiration can result in axillary intertrigo. Intertrigo is an inflamed skin condition caused by heat, friction, and moisture. A warm, wet armpit may accommodate the growth of pathogenic bacteria, yeasts, and fungi. The condition is responsible for rash-like...
(axillary) hair, perianal hair, upper lip hair
Moustache
A moustache is facial hair grown on the outer surface of the upper lip. It may or may not be accompanied by a type of beard, a facial hair style grown and cropped to cover most of the lower half of the face.-Etymology:...
, sideburn (preauricular) hair, periareolar hair, and the beard
Beard
A beard is the collection of hair that grows on the chin, cheeks and neck of human beings. Usually, only pubescent or adult males are able to grow beards. However, women with hirsutism may develop a beard...
area. As with most human biological processes, this specific order may vary among some individuals. Arm, leg, chest
Chest hair
The term chest hair is generally used to describe hair that grows on the chest of human males, in the region between the neck and the abdomen. Chest hair, which is a secondary sex characteristic, develops during and after puberty...
, abdominal
Abdominal hair
The term abdominal hair refers to the hair that grows on the abdomen of humans and non-human mammals, in the region between the pubic area and the thorax . The growth of abdominal hair follows the same pattern on nearly all mammals, vertically from the pubic area upwards and from the thorax...
, 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. Facial hair is often present in late adolescence, but may not appear until significantly later. Facial hair will continue to get coarser, darker and thicker for another 2–4 years after puberty. Some men do not develop full facial hair for up to 10 years after the completion of puberty. Chest hair may appear during puberty or years after. Not all men have chest hair.
Voice change and Adam's apple
Under the influence of androgens, the voice box, or larynxLarynx
The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...
, 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
Octave
In music, an octave is the interval between one musical pitch and another with half or double its frequency. The octave relationship is a natural phenomenon that has been referred to as the "basic miracle of music", the use of which is "common in most musical systems"...
, because the longer and thicker vocal folds
Vocal folds
The vocal folds, also known commonly as vocal cords, are composed of twin infoldings of mucous membrane stretched horizontally across the larynx...
have a lower fundamental frequency
Fundamental frequency
The fundamental frequency, often referred to simply as the fundamental and abbreviated f0, is defined as the lowest frequency of a periodic waveform. In terms of a superposition of sinusoids The fundamental frequency, often referred to simply as the fundamental and abbreviated f0, is defined as the...
. Before puberty, the larynx of boys and girls is about equally small. 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. 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 boneBone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s and nearly twice as much skeletal muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
. 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
Gynecomastia
Gynecomastia or Gynaecomastia, , is the abnormal development of large mammary glands in males resulting in breast enlargement. The term comes from the Greek γυνή gyné meaning "woman" and μαστός mastós meaning "breast"...
. 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.Breast development
The first physical sign of puberty in girls is usually a firm, tender lump under the center of the areolaAreola
This article is about the breast tissue. For the entomology term, see the glossary of Lepidopteran terms. For an artistic cloud motif, see aureola. For the cactus feature, see Areole....
of one or both breast
Breast
The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
s, occurring on average at about 10.5 years of age. This is referred to as thelarche
Thelarche
Thelarche is the onset of secondary breast development, usually occurring at the beginning of puberty in girls. Its etymology is from Greek θηλή [tʰelḗ], “nipple” and ἀρχή [arkʰḗ], “beginning, onset”. Thelarche is usually noticed as a firm, tender lump directly under the centre of the nipple...
. 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.
Pubic hair
Pubic hairPubic hair
Pubic hair is hair in the frontal genital area, the crotch, and sometimes at the top of the inside of the legs; these areas form the pubic region....
is often the second noticeable change in puberty, usually within a few months of thelarche. It is referred to as pubarche
Pubarche
Pubarche refers to the first appearance of pubic hair in a child. Pubarche is one of the physical changes of puberty but should not be equated with it since it may occur independently of complete puberty...
. The pubic hairs are usually visible first along the labia. The first few hairs are described as Tanner stage 2. Stage 3 is usually reached within another 6–12 months, when the hairs are too numerous to count and appear on the pubic mound
Mons pubis
In human anatomy or in mammals in general, the mons pubis , also known as the mons veneris or simply the mons, is the adipose tissue lying above the pubic bone of adult females, anterior to the pubic symphysis...
as well. By stage 4, the pubic hairs densely fill the "pubic triangle." Stage 5 refers to spread of pubic hair to the thigh
Thigh
In humans the thigh is the area between the pelvis and the knee. Anatomically, it is part of the lower limb.The single bone in the thigh is called the femur...
s and sometimes as abdominal hair
Abdominal hair
The term abdominal hair refers to the hair that grows on the abdomen of humans and non-human mammals, in the region between the pubic area and the thorax . The growth of abdominal hair follows the same pattern on nearly all mammals, vertically from the pubic area upwards and from the thorax...
upward towards the navel
Navel
The navel is a scar on the abdomen caused when the umbilical cord is removed from a newborn baby...
. In about 15% of girls, the earliest pubic hair appears before breast development begins.
Vagina, uterus, ovaries
The mucosal surfaceMucous membrane
The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...
of the vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
also changes in response to increasing levels of estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
, becoming thicker and duller pink in color (in contrast to the brighter red of the prepubertal vaginal mucosa). Whitish secretions (physiologic leukorrhea
Leukorrhea
Leukorrhea or leucorrhoea is a medical term that denotes a thick, whitish or yellowish vaginal discharge.There are many causes of leukorrhea, the usual one being estrogen imbalance...
) are a normal effect of estrogen as well. In the two years following thelarche, the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
, ovaries
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
, and the follicles
Ovarian follicle
Ovarian follicles are the basic units of female reproductive biology, each of which is composed of roughly spherical aggregations of cells found in the ovary. They contain a single oocyte . These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single...
in the ovaries increase in size. The ovaries usually contain small follicular cyst
Cyst
A cyst is a closed sac, having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :* Acne...
s visible by ultrasound
Medical ultrasonography
Diagnostic sonography is an ultrasound-based diagnostic imaging technique used for visualizing subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions...
.
Menstruation and fertility
The first menstrual bleedingMenstrual cycle
The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....
is referred to as menarche
Menarche
Menarche is the first menstrual cycle, or first menstrual bleeding, in female human beings. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility....
, and typically occurs about two years after thelarche
Thelarche
Thelarche is the onset of secondary breast development, usually occurring at the beginning of puberty in girls. Its etymology is from Greek θηλή [tʰelḗ], “nipple” and ἀρχή [arkʰḗ], “beginning, onset”. Thelarche is usually noticed as a firm, tender lump directly under the centre of the nipple...
. The average age of menarche is 12.5 in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. 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
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
the average age of menarche is 12.72, and in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
it is 12.9. The time between menstrual periods (menses) is not always regular in the first two years after menarche.Ovulation
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
is necessary for fertility
Fertility
Fertility is the natural capability of producing offsprings. As a measure, "fertility rate" is the number of children born per couple, person or population. Fertility differs from fecundity, which is defined as the potential for reproduction...
, but may or may not accompany the earliest menses. 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. 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. 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 pelvisPelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
and thus hips
Hip (anatomy)
In vertebrate anatomy, hip refer to either an anatomical region or a joint.The hip region is located lateral to the gluteal region , inferior to the iliac crest, and overlying the greater trochanter of the femur, or "thigh bone"...
widen (providing a larger birth canal). 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.
Body odor and acne
Rising levels of androgenAndrogen
Androgen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...
s can change the fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
composition of perspiration, resulting in a more "adult" body odor
Body odor
Body odor or body odour, sometimes colloquially abbreviated as B.O., is the smell of bacteria growing on the body. The bacteria multiply rapidly in the presence of sweat, but sweat itself is almost completely odorless to humans....
. 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
Acne vulgaris
Acne vulgaris is a common human skin disease, characterized by areas of skin with seborrhea , comedones , papules , pustules , Nodules and possibly scarring...
, a skin condition that is characteristic of puberty. Acne varies greatly in its severity.
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. 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. 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.
The average age at which puberty begins may be affected by race as well. For example, the average age of menarche
Menarche
Menarche is the first menstrual cycle, or first menstrual bleeding, in female human beings. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility....
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.
Historical shift
The average age at which the onset of puberty occurs has dropped significantly since the 1840s. 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 NorwayNorway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
, 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
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
the average in 1840 was 16.5 years. In Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
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.
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. The genetic association of timing is strongest between mothers and daughters. The specific geneGene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s affecting timing are not yet known. Among the candidates is an androgen receptor
Androgen receptor
The androgen receptor , also known as NR3C4 , is a type of nuclear receptor that is activated by binding of either of the androgenic hormones testosterone or dihydrotestosterone in the cytoplasm and then translocating into the nucleus...
gene.
Researchers 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. Large amounts of incompletely metabolized estrogens and progestagenProgestagen
Progestogens are a group of hormones including progesterone.The progestogens are one of the five major classes of steroid hormones, in addition to the estrogens, androgens, mineralocorticoids, and glucocorticoids. All progestogens are characterized by their basic 21-carbon skeleton, called a...
s from pharmaceutical products are excreted into the sewage systems of large cities, and are sometimes detectable in the environment. Sex steroid
Sex steroid
Sex steroids, also known as gonadal steroids, are steroid hormones that interact with vertebrate androgen or estrogen receptors. Their effects are mediated by slow genomic mechanisms through nuclear receptors as well as by fast nongenomic mechanisms through membrane-associated receptors and...
s 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 receptor
Receptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
s 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
Polychlorinated biphenyl
Polychlorinated biphenyls are a class of organic compounds with 2 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings. The chemical formula for PCBs is C12H10-xClx...
), 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
Precocious puberty
As a medical term, precocious puberty describes puberty occurring at an unusually early age. In most of these children, the process is normal in every respect except the unusually early age, and simply represents a variation of normal development. In a minority of children, the early development is...
, but mild effects and the other potential exposures outlined above would not.
Bisphenol A
Bisphenol A
Bisphenol A is an organic compound with two phenol functional groups. It is used to make polycarbonate plastic and epoxy resins, along with other applications....
(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
Leaching (chemical science)
Leaching is the process of extracting minerals from a solid by dissolving them in a liquid, either in nature or through an industrial process. In the chemical processing industry, leaching has a variety of commercial applications, including separation of metal from ore using acid, and sugar from...
out of plastic into liquids and foods, and the Centers for Disease Control and Prevention
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...
(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.
Nutritional influence
NutritionNutrition
Nutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with a healthy diet....
al factors are the strongest and most obvious environmental factors affecting timing of puberty. Girls are especially sensitive to nutritional regulation because they must contribute all of the nutritional support to a growing fetus. Surplus calorie
Calorie
The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule...
s (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
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
intakes and higher dietary fiber
Dietary fiber
Dietary fiber, dietary fibre, or sometimes roughage is the indigestible portion of plant foods having two main components:* soluble fiber that is readily fermented in the colon into gases and physiologically active byproducts, and* insoluble fiber that is metabolically inert, absorbing water as it...
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 obesityObesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
with an earlier onset of puberty in girls. They have cited obesity as a cause of breast development before nine years and menarche before twelve years. Early puberty in girls can be a harbinger of later health problems.
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 diseaseInflammatory bowel disease
In medicine, inflammatory bowel disease is a group of inflammatory conditions of the colon and small intestine. The major types of IBD are Crohn's disease and ulcerative colitis.-Classification:...
and tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...
have been notorious for such an effect in the last century, while in areas of the underdeveloped world, chronic parasite infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
s are widespread.
Mental illnesses occur in puberty. The brain undergoes significant development by hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s which can contribute to mood disorders such as Major depressive disorder, bipolar disorder
Bipolar disorder
Bipolar disorder or bipolar affective disorder, historically known as manic–depressive disorder, is a psychiatric diagnosis that describes a category of mood disorders defined by the presence of one or more episodes of abnormally elevated energy levels, cognition, and mood with or without one or...
, dysthymia and schizophrenia
Schizophrenia
Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
. Girls aged between 15 and 19 make up 40% of anorexia nervosa
Anorexia nervosa
Anorexia nervosa is an eating disorder characterized by refusal to maintain a healthy body weight and an obsessive fear of gaining weight. Although commonly called "anorexia", that term on its own denotes any symptomatic loss of appetite and is not strictly accurate...
cases.
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 pheromonePheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s, 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
Sexual abuse
Sexual abuse, also referred to as molestation, is the forcing of undesired sexual behavior by one person upon another. When that force is immediate, of short duration, or infrequent, it is called sexual assault. The offender is referred to as a sexual abuser or molester...
in childhood, or who are adopted
International adoption
International adoption is a type of adoption in which an individual or couple becomes the legal and permanent parents of a child that is a national of a different country...
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
Epidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
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
Menarche
Menarche is the first menstrual cycle, or first menstrual bleeding, in female human beings. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility....
article.
Variations of sequence
The sequence of events of pubertal development can occasionally vary. For example, in about 15% of boys and girls, pubarchePubarche
Pubarche refers to the first appearance of pubic hair in a child. Pubarche is one of the physical changes of puberty but should not be equated with it since it may occur independently of complete puberty...
(the first pubic hairs) can precede, respectively, gonadarche
Gonadarche
Gonadarche refers to the earliest gonadal changes of puberty. In response to pituitary gonadotropins, the ovaries in girls and the testes in boys begin to grow and increase the production of the sex steroids, especially estradiol and testosterone....
and thelarche
Thelarche
Thelarche is the onset of secondary breast development, usually occurring at the beginning of puberty in girls. Its etymology is from Greek θηλή [tʰelḗ], “nipple” and ἀρχή [arkʰḗ], “beginning, onset”. Thelarche is usually noticed as a firm, tender lump directly under the centre of the nipple...
by a few months. Rarely, menarche
Menarche
Menarche is the first menstrual cycle, or first menstrual bleeding, in female human beings. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility....
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 hypothalamusHypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, the pituitary
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
, the gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s, and the adrenal gland
Adrenal gland
In mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...
s, 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
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
. A simple description of hormonal puberty is as follows:
- The brain's hypothalamusHypothalamusThe Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
begins to release pulses of GnRH. - Cells in the anterior pituitaryAnterior pituitaryA major organ of the endocrine system, the anterior pituitary, also called the adenohypophysis, is the glandular, anterior lobe of the pituitary gland...
respond by secreting LHLuteinizing hormoneLuteinizing hormone is a hormone produced by the anterior pituitary gland. In females, an acute rise of LH called the LH surge triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone , it stimulates Leydig cell...
and FSH into the circulation. - The ovariesOvaryThe ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
or testes respond to the rising amounts of LH and FSH by growing and beginning to produce estradiolEstradiolEstradiol is a sex hormone. Estradiol is abbreviated E2 as it has 2 hydroxyl groups in its molecular structure. Estrone has 1 and estriol has 3 . Estradiol is about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect...
and testosteroneTestosteroneTestosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
. - 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 nucleusArcuate nucleus
The arcuate nucleus is an aggregation of neurons in the mediobasal hypothalamus, adjacent to the third ventricle and the median eminence...
of the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
is the driver of the reproductive system. It has neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s which generate and release pulses of GnRH into the portal venous system of the pituitary gland
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
. The arcuate nucleus is affected and controlled by neuronal input from other areas of the brain and hormonal input from the gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s, adipose tissue and a variety of other systems.
The pituitary gland
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
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
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
) respond to rising levels of LH and FSH by producing the steroid
Steroid
A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...
sex hormones
Sex steroid
Sex steroids, also known as gonadal steroids, are steroid hormones that interact with vertebrate androgen or estrogen receptors. Their effects are mediated by slow genomic mechanisms through nuclear receptors as well as by fast nongenomic mechanisms through membrane-associated receptors and...
, testosterone
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
and estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
.
The adrenal gland
Adrenal gland
In mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...
s are a second source for steroid hormones. Adrenal maturation, termed adrenarche
Adrenarche
Adrenarche is an early sexual maturation stage in some higher primates that in humans typically occurs at around 6 to 8 years of age. During adrenarche the adrenal cortex secretes increased levels of androgens such as DHEA and DHEAS, but without increased cortisol levels. Adrenarche is the result...
, typically precedes gonadarche in mid-childhood.
Major hormones
- Neurokinin BNeurokinin BNeurokinin B is a tachykinin peptide.It is found in higher concentration in pregnant women suffering pre-eclampsia and can bind the immune-cloaking molecule phosphocholine....
(a tachykinin peptidePeptidePeptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
) and kisspeptinKisspeptinKisspeptin , the product of the gene , is a G-protein coupled receptor ligand for GPR54. Kiss1 was originally identified as a human metastasis suppressor gene that has the ability to suppress melanoma and breast cancer metastasis...
(a neuropeptideNeuropeptideNeuropeptides are small protein-like molecules used by neurons to communicate with each other. They are neuronal signaling molecules, influence the activity of the brain in specific ways and are thus involved in particular brain functions, like analgesia, reward, food intake, learning and...
), both present in the same hypothalamicHypothalamusThe Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
neuronNeuronA neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s, are critical parts of the control system that switches on the release of GnRH at the start of puberty. - GnRH (gonadotropinGonadotropinGonadotropins are protein hormones secreted by gonadotrope cells of the pituitary gland of vertebrates. This is a family of proteins, which include the mammalian hormones follitropin , lutropin , placental chorionic gonadotropins hCG and eCG and chorionic gonadotropin , as well as at least two...
-releasing hormone) is a peptidePeptidePeptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
hormoneHormoneA hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
released from the hypothalamusHypothalamusThe Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
which stimulates gonadotropeGonadotropeGonadotropes are endocrine cells in the anterior pituitary that produce the gonadotropins, follicle-stimulating hormone and luteinizing hormone...
cells of the anterior pituitaryPituitary glandIn vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
. - LHLuteinizing hormoneLuteinizing hormone is a hormone produced by the anterior pituitary gland. In females, an acute rise of LH called the LH surge triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone , it stimulates Leydig cell...
(luteinizing hormone) is a larger proteinProteinProteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
hormone secreted into the general circulation by gonadotrope cells of the anterior pituitary glandPituitary glandIn vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
. The main target cells of LH are the Leydig cellLeydig cellLeydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone...
s of testesTesticleThe testicle is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system...
and the theca cells of the ovariesOvaryThe ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
. LH secretion changes more dramatically with the initiation of puberty than FSH, as LH levels increase about 25-fold with the onset of puberty, compared with the 2.5-fold increase of FSH. - FSHFollicle-stimulating hormoneFollicle-stimulating hormone is a hormone found in humans and other animals. It is synthesized and secreted by gonadotrophs of the anterior pituitary gland. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and Luteinizing hormone act...
(follicleOvarian follicleOvarian follicles are the basic units of female reproductive biology, each of which is composed of roughly spherical aggregations of cells found in the ovary. They contain a single oocyte . These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single...
stimulating hormone) is another protein hormone secreted into the general circulation by the gonadotropeGonadotropeGonadotropes are endocrine cells in the anterior pituitary that produce the gonadotropins, follicle-stimulating hormone and luteinizing hormone...
cells of the anterior pituitary. The main target cells of FSH are the ovarian follicleOvarian follicleOvarian follicles are the basic units of female reproductive biology, each of which is composed of roughly spherical aggregations of cells found in the ovary. They contain a single oocyte . These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single...
s and the Sertoli cellSertoli cellA Sertoli cell is a 'nurse' cell of the testes that is part of a seminiferous tubule.It is activated by follicle-stimulating hormone and has FSH-receptor on its membranes.-Functions:...
s and spermatogenicSpermatogenesisSpermatogenesis is the process by which male primary germ cells undergo division, and produce a number of cells termed spermatogonia, from which the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two...
tissue of the testesTesticleThe testicle is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system...
. - TestosteroneTestosteroneTestosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
is a steroidSteroidA steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...
hormone produced primarily by the Leydig cellLeydig cellLeydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone...
s of the testesTesticleThe testicle is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system...
, and in lesser amounts by the theca cells of the ovaries and the adrenal cortex. Testosterone is the primary mammalian androgenAndrogenAndrogen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...
and the "original" anabolic steroidAnabolic steroidAnabolic steroids, technically known as anabolic-androgen steroids or colloquially simply as "steroids", are drugs that mimic the effects of testosterone and dihydrotestosterone in the body. They increase protein synthesis within cells, which results in the buildup of cellular tissue ,...
. It acts on androgen receptorAndrogen receptorThe androgen receptor , also known as NR3C4 , is a type of nuclear receptor that is activated by binding of either of the androgenic hormones testosterone or dihydrotestosterone in the cytoplasm and then translocating into the nucleus...
s in responsive tissue throughout the body. - EstradiolEstradiolEstradiol is a sex hormone. Estradiol is abbreviated E2 as it has 2 hydroxyl groups in its molecular structure. Estrone has 1 and estriol has 3 . Estradiol is about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect...
is a steroidSteroidA steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...
hormone produced by aromatization of testosterone. Estradiol is the principal human estrogenEstrogenEstrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
and acts on estrogen receptorEstrogen receptorEstrogen receptor refers to a group of receptors that are activated by the hormone 17β-estradiol . Two types of estrogen receptor exist: ER, which is a member of the nuclear hormone family of intracellular receptors, and the estrogen G protein-coupled receptor GPR30 , which is a G protein-coupled...
s throughout the body. The largest amounts of estradiol are produced by the granulosa cellGranulosa cellA granulosa cell or follicular cell is a somatic cell of the sex cord that is closely associated with the developing female gamete in the ovary of mammals.-Anatomy and function:...
s of the ovariesOvaryThe ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
, but lesser amounts are derived from testicularTesticleThe testicle is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system...
and adrenalAdrenal glandIn mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...
testosterone. - AdrenalAdrenal glandIn mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...
androgenAndrogenAndrogen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...
s are steroids produced by the zona reticulosa of the adrenal cortexAdrenal cortexSituated along the perimeter of the adrenal gland, the adrenal cortex mediates the stress response through the production of mineralocorticoids and glucocorticoids, including aldosterone and cortisol respectively. It is also a secondary site of androgen synthesis.-Layers:Notably, the reticularis in...
in both sexes. The major adrenal androgens are dehydroepiandrosteroneDehydroepiandrosterone5-Dehydroepiandrosterone is a 19-carbon endogenous steroid hormone. It is the major secretory steroidal product of the adrenal glands and is also produced by the gonads and the brain. DHEA is the most abundant circulating steroid in humans....
, androstenedioneAndrostenedioneAndrostenedione is a 19-carbon steroid hormone produced in the adrenal glands and the gonads as an intermediate step in the biochemical pathway that produces the androgen testosterone and the estrogens estrone and estradiol.-Synthesis:Androstenedione is the common precursor of male and female sex...
(which are precursors of testosterone), and dehydroepiandrosterone sulfate which is present in large amounts in the bloodBloodBlood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
. Adrenal androgens contribute to the androgenic events of early puberty in girls. - IGF1 (insulin-like growth factor 1Insulin-like growth factor 1Insulin-like growth factor 1 also known as somatomedin C is a protein that in humans is encoded by the IGF1 gene. IGF-1 has also been referred to as a "sulfation factor" and its effects were termed "nonsuppressible insulin-like activity" in the 1970s.IGF-1 is a hormone similar in molecular...
) rises substantially during puberty in response to rising levels of growth hormoneGrowth hormoneGrowth hormone is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior...
and may be the principal mediator of the pubertal growth spurt. - LeptinLeptinLeptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...
is a protein hormone produced by adipose tissueAdipose tissueIn histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...
. Its primary target organ is the hypothalamusHypothalamusThe Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
. The leptin level seems to provide the brainBrainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
a rough indicator of adipose mass for purposes of regulation of appetiteAppetiteThe appetite is the desire to eat food, felt as hunger. Appetite exists in all higher life-forms, and serves to regulate adequate energy intake to maintain metabolic needs. It is regulated by a close interplay between the digestive tract, adipose tissue and the brain. Decreased desire to eat is...
and energy metabolism. It also plays a permissive role in female puberty, which usually will not proceed until an adequate body mass has been achieved.
Endocrine perspective
The endocrine reproductive systemEndocrine system
In physiology, the endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo"...
becomes functional by the end of the first trimester
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
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 steroid
Sex steroid
Sex steroids, also known as gonadal steroids, are steroid hormones that interact with vertebrate androgen or estrogen receptors. Their effects are mediated by slow genomic mechanisms through nuclear receptors as well as by fast nongenomic mechanisms through membrane-associated receptors and...
s. 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
Sigmund Freud
Sigmund Freud , born Sigismund Schlomo Freud , was an Austrian neurologist who founded the discipline of psychoanalysis...
described.
Gonadotropin
Gonadotropin
Gonadotropins are protein hormones secreted by gonadotrope cells of the pituitary gland of vertebrates. This is a family of proteins, which include the mammalian hormones follitropin , lutropin , placental chorionic gonadotropins hCG and eCG and chorionic gonadotropin , as well as at least two...
and sex steroid levels fall to low levels (nearly undetectable by current clinical assays
Medical test
A diagnostic test is any kind of medical test performed to aid in the diagnosis or detection of disease. For example:* to diagnose diseases, and preferably sub-classify it regarding, for example, severity and treatability...
) 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 cell
Germ cell
A germ cell is any biological cell that gives rise to the gametes of an organism that reproduces sexually. In many animals, the germ cells originate near the gut of an embryo and migrate to the developing gonads. There, they undergo cell division of two types, mitosis and meiosis, followed by...
s (future egg
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
s) 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
Leptin
Leptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...
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"). In the years preceding physical puberty, Robert M. Boyar
Robert M. Boyar
Robert M. Boyar was a physician and endocrinologist known for his studies of the neuroendocrinology of puberty.-Early years and education:...
discovered that the gonadotropin pulses occur only during sleep, but as puberty progresses they can be detected during the day. 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
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
of oscillators in the brain. By this mechanism, the gonadotropin pulses that occur primarily at night just before puberty represent beats
Beat (acoustics)
In acoustics, a beat is an interference between two sounds of slightly different frequencies, perceived as periodic variations in volume whose rate is the difference between the two frequencies....
.
An array of "autoamplification processes" increases the production of all of the pubertal hormones of the hypothalamus, pituitary, and gonads.
Regulation of adrenarche
Adrenarche
Adrenarche is an early sexual maturation stage in some higher primates that in humans typically occurs at around 6 to 8 years of age. During adrenarche the adrenal cortex secretes increased levels of androgens such as DHEA and DHEAS, but without increased cortisol levels. Adrenarche is the result...
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 androgen
Androgen
Androgen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...
s (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
Pubarche
Pubarche refers to the first appearance of pubic hair in a child. Pubarche is one of the physical changes of puberty but should not be equated with it since it may occur independently of complete puberty...
), adult body odor
Body odor
Body odor or body odour, sometimes colloquially abbreviated as B.O., is the smell of bacteria growing on the body. The bacteria multiply rapidly in the presence of sweat, but sweat itself is almost completely odorless to humans....
, 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
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
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
Gynecomastia
Gynecomastia or Gynaecomastia, , is the abnormal development of large mammary glands in males resulting in breast enlargement. The term comes from the Greek γυνή gyné meaning "woman" and μαστός mastós meaning "breast"...
) in a large proportion of boys. Boys who develop mild gynecomastia
Gynecomastia
Gynecomastia or Gynaecomastia, , is the abnormal development of large mammary glands in males resulting in breast enlargement. The term comes from the Greek γυνή gyné meaning "woman" and μαστός mastós meaning "breast"...
or even developing swelling
Swelling (medical)
In medical parlance, swelling is the transient enlargement or protuberance in the body and may include tumors. According to cause, it may be congenital, traumatic, inflammatory, neoplastic or miscellaneous....
s under nipple
Nipple
In its most general form, a nipple is a structure from which a fluid emanates. More specifically, it is the projection on the breasts or udder of a mammal by which breast milk is delivered to a mother's young. In this sense, it is often called a teat, especially when referring to non-humans, and...
s during puberty are told the effects are temporary in some male teenagers due to high levels of estradiol
Estradiol
Estradiol is a sex hormone. Estradiol is abbreviated E2 as it has 2 hydroxyl groups in its molecular structure. Estrone has 1 and estriol has 3 . Estradiol is about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect...
.
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
Dihydrotestosterone
Dihydrotestosterone is an androgen or male sex hormone. The enzyme 5α-reductase synthesises DHT in the prostate, testes, hair follicles, and adrenal glands...
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 progesteroneProgesterone
Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species...
. Much of the testosterone moves into nearby cells called granulosa cell
Granulosa cell
A granulosa cell or follicular cell is a somatic cell of the sex cord that is closely associated with the developing female gamete in the ovary of mammals.-Anatomy and function:...
s. Smaller increases of FSH induce an increase in the aromatase
Aromatase
Aromatase is an enzyme responsible for a key step in the biosynthesis of estrogens. It is a member of the cytochrome P450 superfamily , which are monooxygenases that catalyze many reactions involved in steroidogenesis. In particular, aromatase is responsible for the aromatization of androgens into...
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
Breast
The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
growth
Human development (biology)
Human development is the process of growing to maturity. In biological terms, this entails growth from a one-celled zygote to an adult human being.- Biological development:...
, increased fat composition, growth of the uterus, increased thickness of the endometrium
Endometrium
-Function:The endometrium is the innermost glandular layer and functions as a lining for the uterus, preventing adhesions between the opposed walls of the myometrium, thereby maintaining the patency of the uterine cavity. During the menstrual cycle or estrous cycle, the endometrium grows to a...
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
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
.
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
Insulin-like growth factor 1
Insulin-like growth factor 1 also known as somatomedin C is a protein that in humans is encoded by the IGF1 gene. IGF-1 has also been referred to as a "sulfation factor" and its effects were termed "nonsuppressible insulin-like activity" in the 1970s.IGF-1 is a hormone similar in molecular...
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
- adrenarcheAdrenarcheAdrenarche is an early sexual maturation stage in some higher primates that in humans typically occurs at around 6 to 8 years of age. During adrenarche the adrenal cortex secretes increased levels of androgens such as DHEA and DHEAS, but without increased cortisol levels. Adrenarche is the result...
(approximately age 7) - gonadarcheGonadarcheGonadarche refers to the earliest gonadal changes of puberty. In response to pituitary gonadotropins, the ovaries in girls and the testes in boys begin to grow and increase the production of the sex steroids, especially estradiol and testosterone....
(approximately age 8) - thelarcheThelarcheThelarche is the onset of secondary breast development, usually occurring at the beginning of puberty in girls. Its etymology is from Greek θηλή [tʰelḗ], “nipple” and ἀρχή [arkʰḗ], “beginning, onset”. Thelarche is usually noticed as a firm, tender lump directly under the centre of the nipple...
(approximately age 11 in females) - pubarchePubarchePubarche refers to the first appearance of pubic hair in a child. Pubarche is one of the physical changes of puberty but should not be equated with it since it may occur independently of complete puberty...
(approximately age 12) - menarcheMenarcheMenarche is the first menstrual cycle, or first menstrual bleeding, in female human beings. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility....
(approximately age 12.5 in females) - spermarcheSpermarcheThe first ejaculatory experience of boys is termed semenarche.Spermarche refers to the beginning of development of sperm in boys' testicles at puberty. It contrasts with menarche in girls. Depending on their upbringing, cultural differences, and prior sexual knowledge, boys may have different...
(in males)
See also
- Adolescent sexualityAdolescent sexualityAdolescent sexuality refers to sexual feelings, behavior and development in adolescents and is a stage of human sexuality. Sexuality is often a vital aspect of teenagers' lives...
- Child sexualityChild sexualityChild sexuality is the sexual feelings, behaviors, and development of children.-Freud:Until Sigmund Freud published his Three Essays on the Theory of Sexuality in 1905, children were often regarded as asexual, having no sexuality until later development. Freud was one of the first researchers to...
- Delayed pubertyDelayed pubertyPuberty is described as delayed puberty with exceptions when an organism has passed the usual age of onset of puberty with no physical or hormonal signs that it is beginning. Puberty may be delayed for several years and still occur normally, in which case it is considered constitutional delay, a...
- EunuchEunuchA eunuch is a person born male most commonly castrated, typically early enough in his life for this change to have major hormonal consequences...
- HebephiliaHebephiliaHebephilia refers to the sexual preference for individuals in the early years of puberty . Girls typically begin the process of puberty at age 10 or 11; boys at age 11 or 12...
- Precocious pubertyPrecocious pubertyAs a medical term, precocious puberty describes puberty occurring at an unusually early age. In most of these children, the process is normal in every respect except the unusually early age, and simply represents a variation of normal development. In a minority of children, the early development is...
- Secondary sex characteristicSecondary sex characteristicSecondary sex characteristics are features that distinguish the two sexes of a species, but that are not directly part of the reproductive system. They are believed to be the product of sexual selection for traits which give an individual an advantage over its rivals in courtship and aggressive...
- PuberphoniaPuberphoniaPuberphonia is the persistence of adolescent voice even after puberty.-Introduction:...
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. 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. 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
- Support for teens
- NIH guide to puberty and adolescence
- Growing Up Sexually: A World Atlas
- Pictures and detailed information about breast development during puberty
- Research shows how evolution explains age of puberty, ScienceDaily, December 1, 2005.
- Puberty in girls: interactive animation of Tanner stages
- Puberty in boys: interactive animation of Tanner stages