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Puberty is best considered as one stage in the continuing process of growth and development that begins during gestation and continues until the end of reproductive life. After an interval of childhood quiescence—the juvenile pause—the hypothalamic pulse generator increases activity in the peripubertal period, just before the physical changes of puberty commence. This leads to increased secretion of pituitary gonadotropins and, subsequently, gonadal sex steroids that bring about secondary sexual development, the pubertal growth spurt, and fertility. Historical records show that the age at menarche in girls in Western countries has steadily declined over the last several hundred years; this is probably due to improvements in socioeconomic conditions, nutrition, and, therefore, the general state of health during that period. This trend appears to be continuing but now due to the effects of the obesity epidemic rather than the improvement in general health.
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Many endogenous and exogenous factors can alter age at onset of puberty. While obesity may decrease the age of onset of puberty in girls, chronic illness and malnutrition often delay puberty. There is a significant concordance of age at menarche between mother-daughter pairs and within ethnic populations, indicating the influence of genetic factors. Recent study of genetic loci associated with the age of onset of puberty identified several genes that are likely involved in the regulation of menarche and puberty.
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PHYSIOLOGY OF PUBERTY
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Physical Changes Associated with Puberty
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Descriptive standards proposed by Tanner for assessing pubertal development in males and females are in wide use (denoted as Sexual Maturation stages or, often, Tanner stages). They focus attention on specific details of the examination and make it possible to objectively record subtle progression of secondary sexual development that may otherwise be overlooked. Self-assessment of pubertal development by subjects using reference pictures is used in clinical studies but reliability is less than that achieved by physical examination.
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An early sign of puberty in the female, as noted in longitudinal studies, is an increase in height velocity that heralds the beginning of ...