The brain undergoes significant development by hormones which can contribute to mood disorders such as major depressive disorder , bipolar disorder , dysthymia and schizophrenia. Some of the least understood environmental influences on timing of puberty are social and psychological. In comparison with the effects of genetics, nutrition, and general health, social influences are small, shifting timing by a few months rather than years.
Mechanisms of these social effects are unknown, though a variety of physiological processes, including pheromones , have been suggested based on animal research. The most important part of a child's psychosocial environment is the family, and most of the social influence research has investigated features of family structure and function in relation to earlier or later female puberty. Most of the studies have reported that menarche may occur a few months earlier in girls in high-stress households, whose fathers are absent during their early childhood, who have a stepfather in the home, who are subjected to prolonged sexual abuse in childhood, or who are adopted from a developing country at a young age.
Conversely, menarche may be slightly later when a girl grows up in a large family with a biological father present. More extreme degrees of environmental stress, such as wartime refugee status with threat to physical survival, have been found to be associated with delay of maturation, an effect that may be compounded by dietary inadequacy.
Most of these reported social effects are small and our understanding is incomplete. Most of these "effects" are statistical associations revealed by epidemiologic surveys. Statistical associations are not necessarily causal, and a variety of covariables and alternative explanations can be imagined. Effects of such small size can never be confirmed or refuted for any individual child.
Furthermore, interpretations of the data are politically controversial because of the ease with which this type of research can be used for political advocacy. Accusations of bias based on political agenda sometimes accompany scientific criticism. Another limitation of the social research is that nearly all of it has concerned girls, partly because female puberty requires greater physiologic resources and partly because it involves a unique event menarche that makes survey research into female puberty much simpler than male.
More detail is provided in the menarche article. The sequence of events of pubertal development can occasionally vary. 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.
Learn more about Puberty
The endocrine reproductive system consists of the hypothalamus , the pituitary , the gonads , and the adrenal glands , with input and regulation from many other body systems. True puberty is often termed "central puberty" because it begins as a process of the central nervous system. A simple description of hormonal puberty is as follows:.
The arcuate nucleus of the hypothalamus is the driver of the reproductive system. It has neurons which generate and release pulses of GnRH into the portal venous system of the pituitary gland. The arcuate nucleus is affected and controlled by neuronal input from other areas of the brain and hormonal input from the gonads , adipose tissue and a variety of other systems.
The pituitary gland responds to the pulsed GnRH signals by releasing LH and FSH into the blood of the general circulation, also in a pulsatile pattern. The gonads testes and ovaries respond to rising levels of LH and FSH by producing the steroid sex hormones , testosterone and estrogen. The adrenal glands are a second source for steroid hormones. Adrenal maturation, termed adrenarche , typically precedes gonadarche in mid-childhood. The endocrine reproductive system becomes functional by the end of the first trimester of fetal life.
The testes and ovaries become briefly inactive around the time of birth but resume hormonal activity until several months after birth, when incompletely understood mechanisms in the brain begin to suppress the activity of the arcuate nucleus. This has been referred to as maturation of the prepubertal "gonadostat," which becomes sensitive to negative feedback by sex steroids. The period of hormonal activity until several months after birth, followed by suppression of activity, may correspond to the period of infant sexuality, followed by a latency stage , which Sigmund Freud described.
Gonadotropin and sex steroid levels fall to low levels nearly undetectable by current clinical assays for approximately another 8 to 10 years of childhood.
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Evidence is accumulating that the reproductive system is not totally inactive during the childhood years. Subtle increases in gonadotropin pulses occur, and ovarian follicles surrounding germ cells future eggs double in number. Normal puberty is initiated in the hypothalamus, with de-inhibition of the pulse generator in the arcuate nucleus.
This inhibition of the arcuate nucleus is an ongoing active suppression by other areas of the brain. The signal and mechanism releasing the arcuate nucleus from inhibition have been the subject of investigation for decades and remain incompletely understood. Leptin levels rise throughout childhood and play a part in allowing the arcuate nucleus to resume operation. If the childhood inhibition of the arcuate nucleus is interrupted prematurely by injury to the brain, it may resume pulsatile gonadotropin release and puberty will begin at an early age.
Neurons of the arcuate nucleus secrete gonadotropin releasing hormone GnRH into the blood of the pituitary portal system. 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". Boyar discovered that the gonadotropin pulses occur only during sleep, but as puberty progresses they can be detected during the day. Some investigators have attributed the onset of puberty to a resonance of oscillators in the brain.
An array of "autoamplification processes" increases the production of all of the pubertal hormones of the hypothalamus, pituitary, and gonads [ citation needed ]. Regulation of adrenarche and its relationship to maturation of the hypothalamic-gonadal axis is not fully understood, and some evidence suggests it is a parallel but largely independent process coincident with or even preceding central puberty.
Why are girls hitting early puberty? - Times of India
Rising levels of adrenal androgens termed adrenarche can usually be detected between 6 and 11 years of age, even before the increasing gonadotropin pulses of hypothalamic puberty. Adrenal androgens contribute to the development of pubic hair pubarche , adult body odor , and other androgenic changes in both sexes. The primary clinical significance of the distinction between adrenarche and gonadarche is that pubic hair and body odor changes by themselves do not prove that central puberty is underway for an individual child.
Early stages of male hypothalamic maturation seem to be very similar to the early stages of female puberty, though occurring about 1—2 years later. LH stimulates the Leydig cells of the testes to make testosterone and blood levels begin to rise. For much of puberty, nighttime levels of testosterone are higher than daytime. Regularity of frequency and amplitude of gonadotropin pulses seems to be less necessary for progression of male than female puberty. However, a significant portion of testosterone in adolescent boys is converted to estradiol.
Early Puberty: Causes and Consequences
Estradiol mediates the growth spurt, bone maturation, and epiphyseal closure in boys just as in girls. Estradiol also induces at least modest development of breast tissue gynecomastia in a large proportion of boys. Boys who develop mild gynecomastia or even developing swellings under nipples during puberty are told the effects are temporary in some male teenagers due to high levels of estradiol.
Another hormonal change in males takes place during the teenage years for most young men. At this point in a male's 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. As the amplitude of LH pulses increases, the theca cells of the ovaries begin to produce testosterone and smaller amounts of progesterone.
Much of the testosterone moves into nearby cells called granulosa cells. Smaller increases of FSH induce an increase in the aromatase activity of these granulosa cells, which converts most of the testosterone to estradiol for secretion into the circulation.
The remaining testosterone, together with adrenal androgens is responsible for the typical androgenic changes of female puberty: pubic hair, other androgenic hair as outlined above, body odor, acne. The bioactivity of testosterone is to a large degree limited by SHBG which in turn is mainly controlled by estradiol and prolactin levels estradiol stimulates, prolactin decreases SHBG synthesis.
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. 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. From Wikipedia, the free encyclopedia. For sexual development of non-human organisms, see Sexual maturity. For the Chinese film, see Pubescence film. Developmental stage theories. This section needs additional citations for verification.
Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. See also: Tanner scale. Main article: Voice change. This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Human Development: A Lifespan View 5th ed. Cengage Learning.
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Women's Gynecologic Health. The changes that occur during puberty usually happen in an ordered sequence, beginning with thelarche breast development at around age 10 or 11, followed by adrenarche growth of pubic hair due to androgen stimulation , peak height velocity, and finally menarche the onset of menses , which usually occurs around age 12 or Phillips Encyclopedia of Educational Theory and Philosophy. Sage Publications. On average, the onset of puberty is about 18 months earlier for girls usually starting around the age of 10 or 11 and lasting until they are 15 to 17 than for boys who usually begin puberty at about the age of 11 to 12 and complete it by the age of 16 to 17, on average.
The Daily Telegraph. Health Perspect. Onions ed. Oxford University Press, , p. University of Maryland. Retrieved July 5, Physical growth and development.
Comprehensive Adolescent Health Care. St Louis: Quality Medical Publishing; The essential roles of estrogens in pubertal growth, epiphyseal fusion and bone turnover: lessons from mutations in the genes for aromatase and the estrogen receptor". Hormone Research.