Menarche onset

Menarche Onset in Humans Since most rodent developmental studies have reported accelerated vaginal opening with 4-NP administration, researchers have compared secondary sexual characteristics and menarche onset in Taiwanese girls to levels of 4-NP in collected urine in 786 female students (Chen et al. 2009). After controlling for age and body mass index, urinary 4-NP levels were significantly inversely related to age of menarche, suggesting that further study is needed to determine if the earlier onset of menarche is related to NP exposure. 

Menarche The onset of menstrual periods, usually occurring between the ages of 10 and 17. 

At the time of menarche or puberty, there may be only 300 000 -400 000 oocytes in the ovaries. With the onset of puberty, a second layer begins to form from cuboidal granulosa cells these cells arise from a small number of growing follicles that have an enlarged ooplasm and a zona pellucida. 

A loss of primary oocytes will irreversibly affect a woman s fecundity, but this is difficult to measure directly. Reproductive dysfunction can be studied by the evaluation of irregularities of menstrual cycles and onset of menarche and menopause. However, menstrual cyclicity and onset of menopause and menarche are affected by many parameters, such as age, genetics, nutritional status, stress, exercise, certain drugs and the use of contraceptives that alter endocrine feedback. The length of the menstrual cycle, particularly the follicular phase (before ovulation), can vary between individuals and may make it difficult to measure significant effects in groups of women (Burch et al., 1967 Treloar et al., 1967). 

In Japanese children with precocious puberty treated with leuprolide the time between the last injection and the median onset of menarche was 15 (range 3.6-63) months (25). The age at menarche was higher than that of the healthy population (13 versus 12 years). 

Girls begin menstruating at the onset of puberty, at about the age of 12 or 13, although the onset of menstruation may be earlier or later, depending on the amount of body fat. The first menstrual period is called the menarche during the first few cycles, ovulation may be absent. 

The development in subjects receiving the diet alone was slow, and the effect on height increment and onset of sexual function was strikingly enhanced in those receiving zinc. The zinc-supplemented boys gained considerably more height than those receiving ample protein diet alone. The zinc-supplemented subjects showed evidence of early onset of sexual function, as defined by nocturnal emission in males and menarche in females. The two women described in this report were from hospital clinic and represented the first cases of dwarfism in females because of zinc deficiency (20). 

Although the age at menarche has declined steadily throughout the centuries, probably a result of improved nutrition, the age at menopause onset appears to be relatively stable. However, on average, cigarette smokers experience menopause 2 years earlier than nonsmokers. Women who have undergone hysterectomy also are more likely to have an earlier menopause despite preservation of then-ovaries. Approximately 1% of women develop ovarian failure before the age of 40 years (premature menopause or premature ovarian failure). ... 

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