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The word menopause literally means the permanent physiological, or natural, cessation of menstrual cycles, from the Greek roots \'meno-\' (month) and \'pausis\' (a pause, a cessation). In other words, menopause means the natural and permanent stopping of the monthly female reproductive cycles, and in humans this is usually indicated by a permanent absence of monthly periods or menstruation.
The word is commonly used in regard to human females, where menopause happens more or less in midlife, signaling the end of the fertile phase of a woman\'s life. Menopause is perhaps most easily understood as the opposite process to menarche.
Menopause in women cannot however simply be defined as the permanent "stopping of the monthly periods", because in reality what is happening to the uterus is quite secondary to the process. For medical reasons, the uterus is sometimes surgically removed (hysterectomy) in a younger woman, and after this her periods will cease permanently and the woman will technically be infertile, but as long as her ovaries (or one ovary) are, or is, still functioning, the woman will not be in menopause. This is because even without the uterus, ovulation, and the release of the sequence of reproductive hormones that are an essential part of the reproductive cycles, will continue until the time of menopause is reached.
Menopause is in fact triggered by the faltering and shutting down (or surgical removal) of the ovaries, which are a part of the body\'s endocrine system of hormone production, in this case the hormones which make reproduction possible and influence sexual behavior.
The process of the ovaries shutting down is a phenomenon which involves the entire cascade of a woman\'s reproductive functioning, from brain to skin, and this major physiological event usually has some effect on almost every aspect of a woman\'s body and life.
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Menopause starts as the ovaries begin to fail to be able to produce an egg or ovum every month. Since the process of producing and ripening the egg is also what creates several of the key hormones involved in the monthly cycle, this in turn interrupts the regular pattern of the hormone cycles, and gradually leads to the somewhat chaotic and long-drawn out shutting down of the whole reproductive system.
The break-up in the pattern of the menstrual cycles not only causes the levels of most of the reproductive hormones to drop over time, but also causes the reproductive hormones to fall out of phase with one another, which often leads to extreme and unpredictable fluctuations in the levels, which itself can cause numerous symptoms in most women, such as hot flashes.
After a number of years of erratic functioning, the ovaries almost completely stop producing hormones including the estrogens, progestin and testosterone, and the reproductive system ceases to function.
The average age of menopause is 51 years, and the normal age range for last period ever is somewhere between age 45 to 55. Age 55 to 60 for last period ever is described as a "late menopause". An "early menopause" is defined as last period ever between the age of 40 to 45.
Some women reach menopause at a much younger age than average, especially if they have had cancer or another serious illness, and have undergone chemotherapy. This is sometimes referred to as a "chemical menopause".
Premature menopause (or premature ovarian failure) is defined as last period ever occurring before the age of 40; it occurs in 1% of women and is not viewed as being due to normal causes. Some known causes of spontaneous premature menopause include autoimmune disorders, thyroid disease, and diabetes mellitus, but often it is idiopathic in nature.
Premature menopause is diagnosed or confirmed by measuring the levels of follicle stimulating hormone (FSH) and luteinizing hormone (LH); the levels of these hormones will be higher if menopause has occurred. Rates of premature menopause have been found to be significantly higher in fraternal and identical twins; approximately 5% of twins reach menopause before the age of 40. The reasons for this are not completely understood. Transplants of ovarian tissue between identical twins have been successful in restoring fertility.
Menopause in the animal kingdom appears perhaps to be somewhat rare, although this has not been thoroughly researched. However, it is already quite apparent that humans are not the only species that experience it.
Menopause has been observed in rhesus monkeysWalker ML (1995). "Menopause in female rhesus monkeys". Am J Primatol 35: 59-71. , some cetaceansMcAuliffe K, Whitehead H (2005). "Eusociality, menopause and information in matrilineal whales". Trends Ecol Evolution 20: 650. , as well as in a variety of other species of vertebrates including the guppy, the platyfish, budgerigars or “parakeets”, laboratory rats and mice, the opossum, and all manner of primates
[1] David Reznick1, Michael Bryant, Donna Holmes.
University of California Riverside, United States. david.reznick@ucr.edu
The Grandmother hypothesis suggests that menopause evolved in humans because it promotes the survival of grandchildren. According to the grandmother hypothesis, post reproductive women feed and care for children, adult nursing daughters, and grandchildren whose mothers have weaned them. Human babies require large and steady supplies of glucose to feed the growing brain. In infants in the first year of life, the brain consumes 60% of all calories, so both babies and their mothers require a dependable food supply. Some evidence suggests that hunters contribute less than half the total food budget of most hunter-gatherer societies, and often much less than half, so that foraging grandmothers can contribute substantially to the survival of grandchildren at times when mothers and fathers are unable to gather enough food for all the children. In general, selection operates most powerfully during times of famine or other privation. So although grandmothers might not be necessary during good times, many grandchildren cannot survive without them during times of famine.
Clinically speaking, menopause is a date: for those women who still have a uterus, menopause is defined as the day after a woman\'s last period ever finishes.
In common everyday parlance however, the word "menopause" is usually not used to refer to one day, but to the whole of the menopause transition years. This span of time is also referred to as the change of life or the climacteric and more recently is known as "perimenopause", (literally meaning "around menopause").
Perimenopause means the menopause transition years, the years both before and after the last period ever, when the majority of women find that they undergo at least some symptoms of hormonal change and fluctuation, such as hot flashes, mood changes, insomnia, fatigue, memory problems, etc.
During perimenopause, the production of most of the reproductive hormones, including the estrogens, progesterone and testosterone, diminishes and becomes more irregular, often with wide and unpredictable fluctuations in levels. During this period, fertility diminishes.
Symptoms of perimenopause can begin as early as age 35, although most women become aware of them about 10 years later than this. Perimenopause can last for a few years, or for ten years or even longer. In this respect it resembles puberty, a similar process which surrounds menarche. In fact menopause can usefully be compared to "puberty in reverse", and the psychological challenges and adjustments which take place over this time span can be compared to adolescence.
The actual duration and severity of perimenopause in any individual woman cannot be predicted in advance or during the process. Not every woman experiences symptoms during perimenopause. Approximately one third of all women get no noticeable symptoms other than that their periods become erratic and then stop. Another one third of women have moderate symptoms. The remaining one third of women have very strong symptoms which tend to have a longer duration. The tendency to have a very strong perimenopause may be inherited in some cases.
One piece of recent research appears to show that melatonin supplementation in perimenopausal women can produce a highly significant improvement in thyroid function and gonadotropin levels, as well as restoring fertility and menstruation and preventing the depression associated with the menopauseBellipanni G, DI Marzo F, Blasi F, et al. Effects of melatonin in perimenopausal and menopausal women: our personal experience. 2005. Ann N Y Acad Sci 1057:393-402. DOI: 10.1196/annals.1356.030 PMID 16399909.
Premenopause is a word used to describe the years leading up to the last period ever, when the levels of reproductive hormones are already becoming lower and more erratic, and symptoms of hormone withdrawal may be present.
Postmenopause is all of the time in a woman\'s life that take place after her last period ever, or more accurately, all of the time that follows the point when her ovaries become inactive.
A woman who still has her uterus can be declared to be in post-menopause once she has gone 12 full months with no flow at all, not even any spotting. When she reaches that point, she is one year into post-menopause. The reason for this delay in declaring a woman post-menopausal is because periods become very erratic at this time of life, and therefore a reasonably long stretch of time is necessary to be sure that the cycling has actually ceased.
In women who have no uterus, and therefore have no periods, post-menopause can be determined by a blood test which can reveal the very high levels of Follicle Stimulating Hormone (FSH) that are typical of post-menopausal women.
A woman\'s reproductive hormone levels continue to drop and fluctuate for some time into post-menopause, so any hormone withdrawal symptoms that a woman may be experiencing do not necessarily stop right away, but may take quite some time, even several years, to disappear completely.
Any period-like flow that might occur during post-menopause, even just spotting, must be reported to a doctor. The cause may be minor, but the possibility of endometrial cancer must be checked for and eliminated.
The causes of menopause can be considered from complementary proximate (mechanistic) and ultimate (adaptive evolutionary) perspectives.
From a proximate perspective: A natural or physiological menopause is that which occurs as a part of a woman\'s normal aging process. It is the result of the eventual atresia of almost all oocytes in the ovaries. This causes an increase in circulating follicle stimulating hormone (FSH) and luteinizing hormone (LH) levels as there are a decreased number of oocytes responding to these hormones and producing estrogen. This decrease in the production of estrogen leads to the perimenopausal symptoms of hot flashes, insomnia and mood changes, as well as post-menopausal osteoporosis and vaginal atrophy.
However, menopause can be surgically induced by bilateral salpingo-oophorectomy (removal of both ovaries and both fallopian tubes), which is often, but not always, done in conjunction with hysterectomy. Cessation of menses as a result of removal of the ovaries is called "surgical menopause". The sudden and complete drop in reproductive hormone levels usually produces extreme hormone-withdrawal symptoms such as hot flashes, etc.
As mentioned above, removal of the uterus, hysterectomy, does not itself cause menopause, although pelvic surgery can sometimes precipitate a somewhat earlier menopause, perhaps because of a compromised blood supply to the ovaries. Removing the ovaries however, causes an immediate and powerful "surgical menopause", even if the uterus is left intact.
Cigarette smoking has been found to decrease the age at menopause by as much as one year, and women who have undergone hysterectomy with ovary conservation go through menopause 3.7 years earlier than average. However, premature menopause (before the age of 40) is generally idiopathic.
An ultimate perspective on menopause is given above in the "Menopause in human evolution" section.
As the body struggles to adapt to the rapidly changing levels of natural hormones, a number of symptoms appear. Both users and non-users of hormone replacement therapy identify lack of energy as the most frequent and distressing symptom.
Perimenopausal symptoms, quality of life, and health behaviors in users and nonusers of hormone therapy. PMID 17970860
J Am Acad Nurse Pract. 2007 Nov;19(11):602-13.
Twiss JJ, Wegner J, Hunter M, Kelsay M, Rathe-Hart M, Salado W.
University of Nebraska Medical Center, College of Nursing, Omaha, Nebraska 68198-6330, USA. jtwiss@unmc.edu
PURPOSE: This pilot study was designed to determine the difference in frequency and distress related to perimenopausal symptoms in users and nonusers of hormone therapy (HT), to identify the difference in quality of life (QoL) indicators, and to determine if there is a relationship between QoL and frequency and distress of symptoms for users and nonusers of HT between the ages of 40 and 55 years.
DATA SOURCE: Self-reported responses to the Perimenopause Assessment Questionnaire with five QoL indicators imbedded, the Women\'s Health Assessment Scale, height, weight, and body mass index from 77 users and 89 nonusers of HT.
CONCLUSIONS: More users reported using HT to control perimenopausal symptoms than for birth control or gynecological problems. Nonusers reported a higher percentage of a variety of symptoms compared to users, with more psychosomatic symptoms being reported. Both groups identified lack of energy as the most frequent and distressful symptom. There was a significant difference in frequency of symptoms between groups and a significant difference in distress of symptoms. There were significant negative correlations with the five QoL indicators and frequency and distress of symptoms for users and nonusers of HT, with exception of stress and frequency of symptoms for users. More psychosomatic symptoms were correlated with QoL for nonusers. Cold sweats, loss of interest, miserable and sad, and life not worth living were highly significant for nonusers with QoL, while feeling unattractive, decreased well-being, and lack of enjoyment for users was highly significant.
IMPLICATIONS FOR PRACTICE: Perimenopause is more than hot flashes and abnormal menses. A checklist of perimenopausal symptoms should be used as an assessment tool at each annual visit or more frequently to determine the significance of the symptoms a woman might be experiencing. Assessing the perimenopausal knowledge base is very important. Most importantly, there is a need for perimenopausal educational programs to be developed and implemented.
PMID: 17970860 [PubMed - indexed for MEDLINE]
Other symptoms include vasomotor symptoms such as hot flashes and palpitations, psychological symptoms such as depression, anxiety, irritability, mood swings and lack of concentration, and atrophic symptoms such as vaginal dryness and urgency of urination. Together with these symptoms, the average woman also has increasingly erratic menstrual periods.
These perimenopause symptoms are caused by an overall drop, as well as dramatic but erratic fluctuations, in the levels of estrogens, progestin, and testosterone. Some of these symptoms, such as formication, may be associated directly with hormone withdrawal.
Vasomotor instability
Urogenital atrophy, (main article see Atrophic vaginitis)
Skeletal
Skin, soft tissue
Psychological
Sexual
One cohort study found that menopause was associated with hot flashes; joint pain and muscle pain; and depressed mood.Freeman EW, Sammel MD, Lin H, et al (2007). "Symptoms associated with menopausal transition and reproductive hormones in midlife women". Obstetrics and gynecology 110 (2 Pt 1): 230-40. doi:10.1097/01.AOG.0000270153.59102.40. PMID 17666595. In the same study, it appeared that menopause was not associated with poor sleep, decreased libido, and vaginal dryness.
Perimenopause is a natural stage of life, but when the symptoms are severe, they may be alleviated through medical treatments. Hormone replacement therapy (US abbr.) (HT is the preferred British abbr.) and SSRIs provide the best relief, but equine estrogens and synthetic progestin forms of HRT appear to increase health risks, especially in women who start this treatment after menopause.
A six month placebo-controlled Italian clinical trial of nocturnal administration of three mg. of synthetic melatonin found a remarkable and highly significant improvement in perimenopausal and menopausal women of thyroid function, positive changes of gonadotropins towards more juvenile levels, and abrogation of menopause-related depression in women receiving melatonin versus a placebo.
Effects of melatonin in perimenopausal and menopausal women: our personal experience.
Ann N Y Acad Sci. 2005 Dec;1057:393-402. Bellipanni G, DI Marzo F, Blasi F, Di Marzo A.
Menopause Center, Madonna della Grazie Health Institute, Via Salvo D\'Acquisto 67, 00049 Velletri (Rome), Italy. giuliobellipanni@yahoo.it
The purpose of this clinical trial on possible effects of nocturnal MEL administration in perimenopausal women was to find if MEL by itself modifies levels of hormones and produces changes of any kind, independently of age (42-62 years of age) and the stage of the menstrual cycle. It is accepted that a close link exists between the pineal gland, MEL, and human reproduction and that a relationship exists between adenohypophyseal and steroid hormones and MEL during the ovarian cycle, perimenopause, and menopause.
Subjects took a daily dose of 3 mg synthetic melatonin or a placebo for 6 months. Levels of melatonin were determined from five daily saliva samples taken at fixed times. Hormone levels were determined from blood samples three times over the 6-month period.
Our results indicate that a cause-effect relationship between the decline of nocturnal levels of MEL and onset of menopause may exist.
The follow up controls show that MEL abrogates hormonal, menopause-related neurovegetative disturbances and restores menstrual cyclicity and fertility in perimenopausal or menopausal women.
At present we assert that the six-month treatment with MEL produced a remarkable and highly significant improvement of thyroid function, positive changes of gonadotropins towards more juvenile levels, and abrogation of menopause-related depression.
PMID: 16399909 [PubMed - indexed for MEDLINE]
Some other drugs afford limited relief from hot flashes. A woman and her doctor should carefully review her symptoms and relative risk before determining whether the benefits of HT/HRT or other therapies outweigh the risks. Until more becomes understood about the possible risk, women who elect to use hormone replacement therapy are generally well advised to take the lowest effective dose of hormones for the shortest period possible, and to question their doctors as to whether certain forms might pose fewer dangers of clots or cancer than others.
In addition to relief from hot flashes, hormone therapy remains an effective treatment for osteoporosis.
In HT or HRT, one or more estrogens, usually in combination with progesterone, (and sometimes testosterone) are administered, not only to partially compensate for the body\'s loss of these hormones, but also in an attempt to keep the levels of these hormones in the body much more consistent than they are naturally in perimenopause.
In those women who have no uterus (usually due to a previous hysterectomy) estrogen alone is a suitable hormone therapy. Women who still have a uterus need to take progesterone in addition to estrogen, in order to ensure that the endometrium, the lining of the uterus, does not build up too much, which would be a risk for cancer of the endometrium.
There are several types of hormone therapies, with various possible side effects.
Conjugated equine estrogens contain estrogen molecules conjugated to hydrophilic side groups (e.g. sulfate) and are produced from the urine of pregnant Equidae (horses) mares. Premarin is the prime example of this, either alone or in Prempro, where it is combined with a synthetic progestin, medroxyprogesterone acetate. However Premarin, and especially Prempro, are associated with serious health risks.http://en.wikipedia.orgHormone_replacement_therapy_(menopause)#Types_of_Hormone_Replacement_Therapy Types
In January 2003, the FDA required Wyeth to affix a "black box" warning to PremPro, stating
"WARNING
Estrogens and progestins should not be used for the prevention of cardiovascular disease. The Women’s Health Initiative (WHI) reported increased risks of myocardial infarction, stroke, invasive breast cancer, pulmonary emboli, and deep vein thrombosis in postmenopausal women during 5 years of treatment with conjugated equine estrogens (0.625 mg) combined with medroxyprogesterone acetate (2.5 mg) relative to placebo (see CLINICAL PHARMACOLOGY, Clinical Studies). Other doses of conjugated estrogens and medroxyprogesterone acetate, and other combinations of estrogens and progestins were not studied in the WHI ... "
Women had been advised for many years by numerous doctors and drug company marketing efforts (at least in the USA) that hormone therapy with conjugated equine estrogens after menopause might reduce their risk of heart disease and prevent various aspects of aging. However, a large, randomized, controlled trial (the Women\'s Health Initiative) found that women undergoing HT or HRT with conjugated equine estrogens (Premarin), whether or not used in combination with a synthetic progestin (Premarin plus Provera, known as Prempro), had an increased risk of breast cancer, heart disease, stroke, and Alzheimer\'s disease. Although this increase in risk was small, but it passed the thresholds that had been established by the researchers in advance as sufficient to ethically require stopping the study.
When these results were reported in 2002, the popular media recognized it as a significant news story, while the manufacturer continued to minimize the degree of risk involved.
If anything, the news stories had understated the degree of risk. Many women discontinued equine estrogens altogether, with or without their doctor\'s approval. The number of prescriptions written for Premarin and PremPro in the United States dropped within a year almost to half of their previous level. This sharp drop in prescriptions for Premarin and Prempro was followed by large and successively larger drops in new breast cancer diagnoses, at six months, one year, and 18 months after the drop in Premarin and Prempro prescriptions, for a cumulative 15% drop by the end of 2003. Prescriptions of Prempro and Premarin fell dramatically in Canada as well, but no similarly dramatic drop in Canada\'s breast cancer rates was observed during the same time period. Studies designed to track the further progression of this trend after 2003 are under way, as well as studies designed to quantify how much of the drop was related to the reduced use of HT/HRT.
The adverse biological effects of xenoestrogens and progestins revealed by studies of Premarin and PremPro do not necessarily generalize to supplementation with human forms of estrogen and progesterone. For example, a pilot study reported in JAMA by Smith, Heckbert, et al.Smith NL, Heckbert SR, Lemaitre RN, et al (2004). "Esterified estrogens and conjugated equine estrogens and the risk of venous thrombosis". JAMA 292 (13): 1581-7. doi:10.1001/jama.292.13.1581. PMID 15467060. found clinical evidence that oral conjugated equine estrogens caused clotting, but the other estrogen compound tested in the same study, bioidentical esterified estrogens, does not. conjugated equine estrogens were found to be associated with increased venous thrombotic risk. In sharp contrast, the study found that users of esterified estrogen had no increase in venous thrombotic risk.
Due to the controversy about Premarin-based hormone therapy, a number of doctors are now moving patients who request hormone therapy to help them through perimenopause, to bioidentical hormone products.
Estrace is a form of the precursor to estrogen in the human body known as estradiol, which products have produced fewer side effects than conjugated equine estrogens"Bioidentical Hormones Come Of Age", Marcelle Pick, OB/GYN Nurse Practitioner; published March 24, 2004; updated June 7, 2007; retrieved June 13, 2007.. Prometrium is a bioidentical progesterone which can be used in conjunction with Estrace.
However, all hormone replacement therapies probably do carry some health risks, including high blood pressure, blood clots, and increased risks of breast and uterine cancers. Women who have had a hysterectomy seem to tolerate estrogen-only therapy better than mixed-hormone therapy.
The anti-seizure medication gabapentin (Neurontin) seems to be second only to HRT in relieving hot flashes.[citation needed]
Antidepressants such as paroxetine (Paxil), Fluoxetine hydrochloride (Prozac), and Venlafaxine hydrochloride (Effexor) have been used with some success in the treatment of hot flashes, improving sleep, mood, and quality of life. Of these, Paxil has been the most studied and may provide the most consistent relief[citation needed]. There is a theoretical reason why SSRI antidepressants might help with memory problems-- they increase circulating levels of the neurotransmitter serotonin in the brain and restore hippocampal function. Prozac has been repackaged as Sarafem and is approved and prescribed for premenstrual dysphoric disorder (PMDD), a mood disorder often exacerbated during perimenopause and early menopause. PMDD has been found by PET scans to be accompanied by a sharp drop in serotonin in the brain and to respond quickly and powerfully to SSRIs.
About as effective as antidepressants for hot flashes, but without the other mind and mood benefits of antidepressants, are blood pressure medicines including clonidine (Catapres). These drugs may merit special consideration by women suffering both from high blood pressure and hot flashes.
Medical non-hormone treatments provide less than complete relief, and each has side effects.
In the area of complementary and alternative therapies, acupuncture treatment is promising. There are some studies indicating positive effects, especially on hot flashes
[2] Nir Y, Huang MI, Schnyer R, Chen B, Manber R. Stanford University School of Medicine, United States. amiryael@gmail.com
[3] Cohen SM, Rousseau ME, Carey BL. University of Pittsburgh, 440 Victoria Bldg, 3500 Victoria St, Pittsburgh, PA 15261, USA. cohensu@pitt.edu
[4] Zaborowska E, Brynhildsen J, Damberg S, Fredriksson M, Lindh-Astrand L, Nedstrand E, Wyon Y, Hammar M. Division of Obstetrics and Gynecology, Department of Molecular and Clinical Medicine, Faculty of Health Sciences, University Hospital, Linköping, Sweden.
[5] Vincent A, Barton DL, Mandrekar JN, Cha SS, Zais T, Wahner-Roedler DL, Keppler MA, Kreitzer MJ, Loprinzi C. Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
showing no positive effects of acupuncture regarding menopause.
There are claims that soy isoflavones are beneficial concerning menopause. However, one study [6] Fournier LR, Ryan Borchers TA, Robison LM, Wiediger M, Park JS, Chew BP, McGuire MK, Sclar DA, Skaer TL, Beerman KA. Department of Psychology, Washington State University, Pullman, WA 99164-4820, USA. Fournier@wsunix.wsu.edu indicated that soy isoflavones did not improve or appreciably affect cognitive functioning in postmenopausal women.
Other remedies that have proven no better than a placebo at treating hot flashes and other menopause symptoms include red clover isoflavone extracts and black cohosh. Black cohosh has potentially serious side-effects such as the stimulation of breast cancer, therefore prolonged administration is not recommended in any case.
Individual counseling or support groups may be helpful to handle sad, depressed, or confusing feelings women may be having as they pass through what can be a very challenging transition time.
Vaginal moisturizers such as Replens can help women with thinning vaginal tissue or dryness, and lubricants such as K-Y Jelly or Astroglide, can help with lubrication difficulties that may be present during intercourse. It is worth pointing out that moisturizers and lubricants are different products for different issues: some women feel unpleasantly dry all of the time apart from during sex, and they may do better with moisturizers all of the time. Those who need only lubricants are fine just using the lubrication products during intercourse.
Low-dose prescription vaginal estrogen products such as Estrace cream or the Estring are generally a safe way to use estrogen topically, in order to help vaginal thinning and dryness problems (see vaginal atrophy) while only minimally increasing the levels of estrogen in the bloodstream.
Lifestyle measures, such as drinking cold liquids, staying in cool rooms, using fans, removing excess clothing layers when hot flashes strike, and avoiding hot flash triggers including hot drinks and spicy foods, may partially supplement (or even obviate) the use of medications for some women.
| Human physiology and endocrinology of reproduction | |
|---|---|
| Anatomy and physiology | Reproductive system (male, female) |
| Menstrual/Estrous cycle | Menstruation - Follicular phase - Ovulation - Luteal phase |
| Gametogenesis | Spermatogenesis (spermatogonium, spermatocyte, spermatid, sperm) - Oogenesis (oogonium, oocyte, ootid, ovum) - Germ cell (gonocyte, gamete) |
| Sexuality | Human sexual behavior - Sexual intercourse - Erection - Ejaculation - Orgasm - Insemination - Fertilisation/Fertility - Masturbation - Pregnancy - Postpartum period |
| Lifespan | Prenatal development - Sexual dimorphism - Sexual differentiation - Puberty (Menarche, Adrenarche) - Maternal age/Paternal age - Climacteric (Menopause, Andropause) |
| Eggs | Ovum - Oviposition - Oviparity - Ovoviviparity - Viviparity |
| Reproductive endocrinology | Hypothalamic-pituitary-gonadal axis - Andrology - Hormone |
Menopause can also be described as a small mouse being regurgitated by a sabre tooth tiger.
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia
