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Estrus Cycle

Estrus cycle

The estrus cycle (also œstrus or estrous cycle) refers to the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females (humans and great apes are the only mammals who undergo a menstrual cycle instead). Estrus cycles start after puberty in sexually mature females and are interrupted by anestrous phases (see below: anestrus). Typically estrus cycles continue until death. Some animals may display bloody vaginal discharge, often mistaken for menstruation.

Differences from the menstrual cycle

Mammals share the same reproductive system, including the regulatory hypothalamic system that releases gonadotropin releasing hormone in pulses, the pituitary that secretes follicle stimulating hormone and luteinizing hormone, and the sex hormones including estrogens and progesterone. However, species vary significantly in the detailed functioning. One difference is that animals that have estrus cycles reabsorb the endometrium if conception does not occur during that cycle. Animals that have menstrual cycles shed the endometrium through menstruation instead. Another difference is sexual activity. In species with estrus cycles, females are generally only sexually active during the estrus phase of their cycle (see below for an explanation of the different phases in an estrus cycle). This is also referred to as being "in heat." In contrast, females of species with menstrual cycles can be sexually active at any time in their cycle, even when they are not about to ovulate. Humans, unlike some other species, do not have any external signs to signal receptivity at ovulation. Research has shown however, that women tend to have more sexual thoughts and are most prone to sexual activity right before ovulation.

Etymology and nomenclature

Estrus is derived from Latin oestrus (frenzy, gadfly), in turn from Greek oistros (gadfly, breeze, sting, mad impulse). Its adjectival form is estrous. The earliest use in English is of "frenzied passion". In 1890 it was first used to describe "rut in animals, heat". Estrus, also œstrus (BE) or heat, is itself part of the estrus cycle. Estrus and estrum are synonyms.

The four phases of the Estrus Cycle

Proestrus

One or several follicles of the ovary are starting to grow, their number being specific for the species. Typically this phase lasts 2-4 days. Under the influence of estrogen the lining in the uterus (endometrium) starts to develop. Some animals may experience vaginal secretions that could be bloody. The female is not yet sexually receptive.

Estrus

Estrus refers to the phase when the female is sexually receptive ("in heat"). Under regulation by gonadotropic hormones ovarian follicles are maturing and estrogen secretions exert their maximal influence. The animal exhibits a sexually receptive behavior, a situation that may be signaled by visible physiologic changes. A signal trait of estrus is the lordosis reflex in which the animal spontaneously elevates her hindquarters. In some species the vulva is reddened. Ovulation may occur spontaneously in some species (e.g. cow), while in others it is induced by copulation (e.g. cat). If there is no copulation in an induced ovulator, estrus may continue for many days, followed by interestrus, and a reentry into the estrus phase until copulation and ovulation occur.

Metestrus

During this phase, the signs of estrogen stimulation subside and the corpus luteum starts to form. The uterine lining is under the influence of progesterone and becomes secretory. This phase typically is brief and may last 1-3-5 days. In some animals bleeding may be noted due to declining estrogen levels.

Diestrus

Diestrus is characterised by the activity of the corpus luteum that produces progesterone. In the absence of pregnancy the diestrus phase (also termed pseudo-pregnancy) terminates with the regression of the corpus luteum. The lining in the uterus is not shed, but will be reorganised for the next cycle.

Anestrus

Anestrus refers to the phase when the sexual cycle rests. This is typically a seasonal event and controlled by light exposure through the pineal gland that releases melatonin. Melatonin may repress stimulation in long-day breeders and stimulate reproduction in short-day breeders. Melatonin is thought to act by regulating hypothalamic pulse activity of GnRH. Other than season, anestrus is induced by pregnancy, lactation, significant illness, and possibly age.

Cycle variability

Cycle variability differs among species, but typically cycles are more frequent in smaller animals. Even within species significant variability can be observed, thus cats may undergo an estrus cycle of 3 to 7 weeks. Domestication can affect estrous cycles due to changes in the environment.

Frequency

Some species—such as cows and pigs—are polyestrous and can go into heat several times a year. Seasonally polyestrous animals have multiple estrous cycles during a specific time of the year and can be divided into short-day and long-day breeders:
- Short-day breeders—such as sheep, goats, deer, elk—are sexually active in fall.
- Long-day breeders—such as horses and hamsters—are sexually active in spring and summer. Species that go into heat twice per year—such as dogs and cats—are diestrous. Monoestrous species—such as bears, foxes, and wolves—have only one breeding season a year, typically in spring to allow growth of the offspring during the warm season to survive the next winter.

Specific species

Cats

The cat in heat (queen) has an estrus of 3-16 days (average 7) and is an induced ovulator. Without copulation she may enter interestrus before reentering estrus. With copulation and in the absence of pregnancy, cycles occur about every three weeks. While polyestrous, cats experience a seasonal anestrus in autumn and early winter.

Dogs

A female dog (bitch) is biestrous and goes into heat typically twice a year. The proestrus is relatively long 5-7 days, while the estrus may last 4-13 days. With a diestrus of 7-10 days a typical cycle lasts about 3 weeks followed by about 150 days of anestrus.

Horses

A mare may be 4 to 10 days in heat and about 14 days in diestrus. Thus a cycle may be short, i.e 3 weeks. Horses mate in spring and summer, autumn is a transition time, and anestrus rules the winter. A feature of the fertility cycle of horses and other large herd animals is that it is usually affected by the seasons. The number of hours daily that light enters the eye of the animal affects the brain, which governs the release of certain precursors and hormones. When daylight hours are few, these animals "shut down," become anestrous, and do not become fertile. As the days grow longer, the longer periods of daylight cause the hormones which activate the breeding cycle to be released. As it happens, this has a sort of utility for these animals in that, given a gestation period of about eleven months, it prevents them from having young when the cold of winter would militate against their survival. This is why animals can reproduce during only certain times of the year.

Others

Estrus frequency of some other mammals:
- Cow - 21 days
- Elephant - 16 weeks
- Goat - 21 days
- Rodents - 4–6 days
- Sow - 21 weeks

External links

- [http://www.siu.edu/~tw3a/431estcy.htm Systematic overview]
- [http://www.etymonline.com/index.php?term=estrus Etymology]
- [http://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/filne_e.htm Cat estrus cycle]
- [http://maine.maine.edu/~rcausey/estrous.HTM Horse estrus cycle]
- See also Winking and Dripping (Horses)
- See also The Female Menstrual Cycle (Humans) Category:Biological reproduction

Hormone

A hormone (from Greek horman - "to set in motion") is a chemical messenger from one cell (or group of cells) to another. All multicellular organisms produce hormones (including plants - see article phytohormone). The best known animal (and human) hormones are those produced by endocrine glands of vertebrate animals, but hormones are produced by nearly every organ system and tissue type in a human or animal body. Hormone molecules are secreted (released) directly into the bloodstream (however, some hormones, called ectohormones are secreted to the outside environment). They move by circulation or diffusion to their target cells, which may be nearby cells (paracrine action) in the same tissue or cells of a distant organ of the body. The function of hormones is to serve as a signal to the target cells; the action of hormones is determined by the pattern of secretion and the signal transduction of the receiving tissue. Hormone actions vary widely, but can include stimulation or inhibition of growth, induction or suppression of apoptosis (programmed cell death), activation or inhibition of the immune system, regulating metabolism and preparation for a new activity (e.g. fighting, fleeing, mating) or phase of life (e.g. puberty, caring for offspring, menopause). In many cases, one hormone may regulate the production and release of other hormones. Many of the responses to hormone signals can be described as serving to regulate metabolic activity of an organ or tissue. Hormones also control the reproductive cycle of virtually all multicellular organisms.

History

The concept of internal secretion developed in the 19th century; Claude Bernard described it in 1855, but did not specifically address the possibility of secretions of one organ acting as messengers to others. Still, various endocrine conditions were recognised and even treated adequately (e.g. hypothyroidism with extract of thyroid glands). The major breakthrough was the identification of secretin, the hormone secreted by the duodenum that stimulates pancreatic secretions, by Ernest Starling and William Bayliss in 1902. Previously, the process had been considered (e.g. by Ivan Pavlov) to be regulated by the nervous system. Starling and Bayliss demonstrated that injecting duodenal extract into dogs rapidly increased pancreatic secretions, raising the possibility of a chemical messenger. Starling is also credited with introducing the term "hormone", having coined it in a 1905 lecture. Later reports indicate it was suggested to him by the Cambridge physiologist William B. Hardy (Henderson 2005). The remainder of the 20th century saw all the major hormones discovered, as well as the cloning of the relevant genes and the identification of the many interlocking feedback mechanisms that characterise the endocrine system.

Physiology of hormones

Every cell is capable of producing a vast number of regulatory molecules. The classical endocrine glands and their hormone products are specialized to serve regulation on the overall organism level, but can in many instances be used in other ways or only on the tissue level. The rate of production of a given hormone is most commonly regulated by a homeostatic control system, generally by negative feedback. Homeostatic regulation of hormones depends, apart from production, on the metabolism and excretion of hormones. Hormone secretion can be stimulated and inhibited by:
- Other hormones (stimulating or releasing-hormones)
- Plasma concentrations of ions or nutrients, as well as binding globulins
- Neurons and mental activity
- Environmental changes, e.g. of light or temperature One special group of hormones are trophic hormones that act as stimulants of hormone production of other endocrine glands. For example: thyroid-stimulating hormone (TSH) causes growth and increased activity of another endocrine gland - the thyroid - hence increasing output of thyroid hormones. A recently identified and studied class of hormones is that of the "Hunger Hormones" - ghrelin, orexin and PYY 3-36 - and their antagonists - e.g. leptin.

Types of hormones

Vertebrate hormones fall into four chemical classes: #Amine-derived hormones are derivatives of the amino acids tyrosine and tryptophan. Examples are catecholamines and thyroxine. #Peptide hormones consist of chains of amino acids. Examples of small peptide hormones are TRH and vasopressin. Peptides composed of scores or hundreds of amino acids are referred to as proteins. Examples of protein hormones include insulin and growth hormone. #Steroid hormones are derived from cholesterol. The adrenal cortex and the gonads are primary sources. Examples of steroid hormones are testosterone and cortisol. Sterol hormones such as calcitriol are a homologous system. #Lipid and phospholipid hormones are derived from lipids such as linoleic acid and phospholipids such as arachidonic acid. The main class is the eicosanoids, which includes the widely studied prostaglandins.

Pharmacology

A large number of hormones are used as medication. The most commonly prescribed hormones are estrogens and progestagens (in the contraceptive pill and as HRT), thyroxine (as levothyroxine, for hypothyroidism) and steroids (for autoimmune diseases and several respiratory disorders). Insulin is used by many diabetics. Local preparations for use in otolaryngology often contain pharmacologic equivalents of adrenalin, while steroid and vitamin D creams are used extensively in dermatological practice. A "pharmacologic dose" of a hormone is a medical usage referring to an amount of a hormone far greater than naturally occurs in a healthy body. The effects of pharmacologic doses of hormones may be different from responses to naturally occurring amounts and may be therapeutically useful. An example is the ability of pharmacologic doses of glucocorticoid to suppress inflammation.

Important human hormones

Spelling is not uniform for many hormones. Current North American and international usage is estrogen, gonadotropin, while British usage retains the Greek diphthong in oestrogen and the unvoiced aspirant h in gonadotrophin.

Amine hormones

Amine-derived hormones:
- adrenaline (or epinephrine)
- dopamine
- melatonin (N-acetyl-5-methoxytryptamine)
- noradrenaline (or norepinephrine)
- serotonin (5-HT)
- thyroxine (T4)
- triiodothyronine (T3)

Peptide hormones

Peptide hormones:
- antimullerian hormone (AMH, also mullerian inhibiting factor or hormone)
- adiponectin (also Acrp30)
- adrenocorticotropic hormone (ACTH, also corticotropin)
- angiotensinogen and angiotensin
- antidiuretic hormone (ADH, also vasopressin, arginine vasopressin, AVP)
- atrial-natriuretic peptide (ANP, also atriopeptin)
- calcitonin
- cholecystokinin (CCK)
- corticotropin-releasing hormone (CRH)
- erythropoietin (EPO)
- follicle stimulating hormone (FSH)
- gastrin
- glucagon
- gonadotropin-releasing hormone (GnRH)
- growth hormone-releasing hormone (GHRH)
- human chorionic gonadotropin (hCG)
- growth hormone (GH or hGH)
- insulin
- insulin-like growth factor (IGF, also somatomedin)
- leptin
- luteinizing hormone (LH)
- melanocyte stimulating hormone (MSH or α-MSH)
- neuropeptide Y
- oxytocin
- parathyroid hormone (PTH)
- prolactin (PRL)
- renin
- secretin
- somatostatin
- thrombopoietin
- thyroid-stimulating hormone (TSH)
- thyrotropin-releasing hormone (TRH)

Steroid and sterol hormones

Steroid hormones:
- Glucocorticoids
- cortisol
- Mineralocorticoids
- aldosterone
- Sex steroids
- Androgens
- testosterone
- dehydroepiandrosterone (DHEA)
- dehydroepiandrosterone sulfate (DHEAS)
- androstenedione
- dihydrotestosterone (DHT)
- Estrogens
- estradiol
- Progestagens
- progesterone
- Progestins Sterol hormones:
- Vitamin D derivatives
- calcitriol

Lipid hormones

Lipid and phospholipid hormones (eicosanoids):
- prostaglandins
- leukotrienes
- prostacyclin
- thromboxane

Reference

- Henderson J. Ernest Starling and 'Hormones': an historical commentary. J Endocrinol 2005;184:5-10. PMID 15642778. Category:Endocrinology Category:Signal transduction ko:호르몬 ja:ホルモン simple:Hormone th:ฮอร์โมน

Placenta

The placenta is an ephemeral (temporary) organ present only in female placental mammals during gestation (pregnancy). The placenta is composed of two parts, one of which is genetically and biologically part of the fetus, the other part of the mother. It is implanted in the wall of the uterus, where it receives nutrients from the mother's blood and passes out waste. This interface forms a barrier, the placental barrier, which filters out many substances which could harm the fetus. However, many other substances are not filtered out, including alcohol. Most viruses also easily cross this barrier. In addition to the transfer of gases and nutrients, the placenta also has metabolic and endocrine activity. It produces, amongst other hormones, progesterone which is important in maintaining the pregnancy, and somatomammotropin (also known as Placental Lactogen) which acts to increase the amount of glucose and lipids in the maternal blood. This results in increased transfer of these nutrients to the fetus and is also the main cause of the increased blood sugar levels seen in pregnancy. The placenta is connected to the fetus via the umbilical cord which is composed of blood vessels and connective tissue. When the fetus is delivered, the placenta is delivered afterwards (and for this reason is often called the afterbirth). After delivery of the placenta the umbilical cord is usually clamped and severed or may be left attached to fall off naturally which is referred to as a Lotus Birth. In most mammalian species, the mother bites the cord and consumes the placenta. The site of the former umbilical cord attachment in the center of the front of the abdomen is known as the umbilicus, or navel, or belly-button.

Non-placental Mammals and Marsupials

The only non-placental mammals are the monotremes, which are egg-laying mammals found only in Australia and New Guinea. Marsupials which are found primarily in Australia may have a rudimentary egg-yolk placenta, which degenerates quite early in foetal development. Bandicoots are the only living example according to Molly Kalafut.[http://www.knowyoursto.com/marsupialia/marsupials.html] A few forms have it according to The Columbia Encyclopedia.[http://www.bartleby.com/65/ma/marsupial.html] -This rudimentary placenta could suggest that marsupials evolved out of placental mammals.- Both marsupials and monotremes represent earlier branching of the basal mammalian lineage.

References

- [http://www.bartleby.com/65/ma/marsupial.html marsupial]
- [http://www.knowyoursto.com/marsupialia/marsupials.html About Marsupials] Category:Developmental biology ja:胎盤

Menstrual cycle

The menstrual cycle is the set of recurring physiological changes in a female's body that are under the control of the reproductive hormone system and necessary for reproduction. In women, menstrual cycles occur typically on a monthly basis between puberty and menopause. Besides humans, only other great apes exhibit menstrual cycles, in contrast to the estrus cycle of most mammalian species. During the menstrual cycle, the sexually mature female body releases one egg (or occasionally two, which might result in dizygotic, or non-identical, twins) at the time of ovulation. The lining of the uterus, the endometrium, builds up in a synchronised fashion. After ovulation, this lining changes to prepare for potential implantation of the fertilised egg to establish a pregnancy. If fertilisation and pregnancy do not ensue, the uterus sheds the lining and a new menstrual cycle begins. The process of the shedding of the lining is called menstruation. Menstruation manifests itself to the outer world in the form of the menses (also menstruum): essentially part of the endometrium and blood products that pass out of the body through the vagina. Although this is commonly referred to as blood, it differs in composition from venous blood. Common usage refers to menstruation and menses as a period. This bleeding serves as a sign that a woman has not become pregnant. (However, this cannot be taken as certainty, as sometimes there is some bleeding in early pregnancy.) During the reproductive years, failure to menstruate may provide the first indication to a woman that she may have become pregnant. A woman might say that her "period is late" when an expected menstruation has not started and she might have become pregnant. Menstruation forms a normal part of a natural cyclic process occurring in healthy women between puberty and the end of the reproductive years. The onset of menstruation, known as menarche, occurs at an average age of 12, but can occur any time between the ages of 8 and 16. The last period, menopause, usually occurs between the ages of 45 and 55. Deviations from this pattern deserve medical attention. Amenorrhea refers to a prolonged absence of menses during the reproductive years of a woman for reasons other than pregnancy. For example, women with very low body fat, such as athletes, may cease to menstruate. The presence of menstruation does not prove that ovulation took place; women who do not ovulate may have menstrual cycles. Those anovulatory cycles tend to take place less regularly and show greater variation in cycle length. In addition, the absence of menstruation also does not prove that ovulation did not take place, because hormone disruptions in non-pregnant women can suppress bleeding on occasion.

The normal menstrual cycle in humans

Women show considerable variation in the lengths of their menstrual cycles, and the length of the menstrual cycle differs in different animals (see below). While cycle length may vary, 28 days is generally taken as representative of the average ovulatory cycle in women. Convention uses the onset of menstrual bleeding to mark the beginning of the cycle, so the first day of bleeding is called "Cycle Day one". One can divide the menstrual cycle into four phases:

Menstruation

Menstruation lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal) and involves the loss of about 50 millilitres of blood (including shed lining). An enzyme called plasmin — contained in the endometrium — inhibits the blood from clotting. Because of this blood loss, women have higher dietary requirements for iron than do males to prevent iron deficiency. Many women experience uterine cramps, also referred to as dysmenorrhea, during this time. A vast industry has grown to provide sanitary products to help women to manage their menses. The tampon is a common product.

Follicular phase

Through the influence of a rise in Follicle stimulating hormone (FSH), five to seven tertiary-stage ovarian follicles are recruited for entry into the menstrual cycle. These follicles, that have been growing for the better part of a year in a process known as folliculogenesis, compete with each other for dominance. In a signal cascade kicked off by luteinizing hormone (LH), the follicles secrete estradiol, a steroid that acts to inhibit pituitary secretion of FSH. With diminished FSH supply comes a slowing in growth that eventually leads to follicle death, known as atresia. The largest follicle secretes inhibin that serves as a finishing blow to less competent follicles by further suppressing FSH. This dominant follicle continues growing, forms a bulge near the surface of the ovary, and soon becomes competent to ovulate. The follicles also secrete estrogens (of which estradiol is a member). Estrogens initiate the formation of a new layer of endometrium in the uterus, histologically identified as the proliferative endometrium. If fertilised, the embryo will implant itself within this hospitable flesh.

Ovulation

embryo When the follicle has matured, it secretes enough estradiol to trigger the acute release of luteinizing hormone (LH). In the average cycle this LH surge starts around cycle day 12 and may last 48 hours. The release of LH matures the egg and weakens the wall of the follicle in the ovary. This process leads to ovulation: the release of the now mature ovum, the largest cell of the body (with a diameter of about 0.5 mm). Which of the two ovaries — left or right — ovulates appears essentially random; no known left/right co-ordination exists. The Fallopian tube needs to capture the egg and provide the site for fertilisation. A characteristic clear and stringy mucus exhibiting spinnbarkeit develops at the cervix, ready to accept sperm from intercourse. In some women, ovulation features a characteristic pain called Mittelschmerz which lasts for several hours. The sudden change in hormones at the time of ovulation also causes light mid-cycle bleeding for some women. Many women perceive the vaginal and cervical mucus changes at ovulation, particularly if they are monitoring themselves for signs of fertility. An unfertilised egg will eventually disintegrate or dissolve in the uterus. Scientific investigations have indicated that the olfactory acuity or the sense of smell is greatest during ovulation in women.

Luteal phase

The corpus luteum is the solid body formed in the ovaries after the egg has been released from the fallopian tube which continues to grow and divide for a while. After ovulation, the residual follicle transforms into the corpus luteum under the support of the pituitary hormones. This corpus luteum will produce progesterone in addition to estrogens for approximately the next 2 weeks. Progesterone plays a vital role in converting the proliferative endometrium into a secretory lining receptive for implantation and supportive of the early pregnancy. It raises the body temperature by half- to one degree Fahrenheit (one-quarter to one-half degree Celsius), thus women who record their temperature on a daily basis will notice that they have entered the luteal phase. If fertilisation of an egg has occurred, it will travel as an early embryo through the tube to the uterine cavity and implant itself 6 to 12 days after ovulation. Shortly after implantation, the growing embryo will signal its existence to the maternal system. One very early signal consists of human chorionic gonadotropin (hCG), a hormone that pregnancy tests can measure. This signal has an important role in maintaining the corpus luteum and enabling it to continue to produce progesterone. In the absence of a pregnancy and without hCG, the corpus luteum demises and inhibin and progesterone levels fall. This will set the stage for the next cycle. Progesterone withdrawal leads to menstrual shedding (progesterone withdrawal bleeding), and falling inhibin levels allow FSH levels to rise to raise a new crop of follicles.

Menstrual symptoms

In many women, various unpleasant symptoms caused by the involved hormones and by cramping of the uterus can precede or accompany menstruation. More severe symptoms may include significant menstrual pain (dysmenorrhea), abdominal pain, migraine headaches, depression and irritability. Some women encounter premenstrual stress syndrome (PMS or premenstrual syndrome), a cyclic clinical entity. Breast discomfort caused by premenstrual water retention is very common. The list of symptoms experienced varies from person to person. Furthermore, within an individual, the severity of the symptoms may vary from cycle to cycle.

The fertile window

The length of the follicular phase — and consequently the length of the menstrual cycle — may vary widely. The luteal phase, however, almost always takes the same number of days. Some women have a luteal phase of 10 days, others of 16 days (the average is 14 days), but for each individual woman, this length will remain constant. Sperm survive inside a woman for 3 days on average, with survival time up to five days considered normal. A pregnancy resulting from sperm life of eight days has been documented . The most fertile period (the time with the highest likelihood of sexual intercourse leading to pregnancy) covers the time from some 5 days before ovulation until 1–2 days after ovulation. In an average 28 day cycle with a 14-day luteal phase, this corresponds to the second and the beginning of the third week of the cycle. Fertility awareness methods of birth control attempt to determine the precise time of ovulation in order to find the relatively fertile and the relatively infertile days in the cycle. People who have heard about the menstrual cycle and ovulation may commonly and mistakenly assume, for contraceptive purposes, that menstrual cycles always take a regular 28 days, and that ovulation always occurs 14 days after beginning of the menses. This assumption may lead to unintended pregnancies. Note too that not every bleeding event counts as a menstruation, and this can mislead people in their calculation of the fertile window. If a woman wants to conceive, the most fertile time occurs between 19 and 10 days prior to the expected menses. Many women use ovulation detection kits that detect the presence of the LH surge in the urine to indicate the most fertile time. Other ovulation detection systems rely on observation of one or more of the three primary fertility signs (basal body temperature, cervical fluid, and cervical position). Among women living closely together, the onsets of menstruation may tend to synchronise somewhat. Researchers first described this phenomenon in 1971, and explained it by the action of pheromones in 1998 (Stern and McClintock 1998). However, subsequent research has called this conclusion into question.

Hormonal control

Extreme intricacies regulate the menstrual cycle. For many years, researchers have argued over which regulatory system has ultimate control: the hypothalamus, the pituitary, or the ovary with its growing follicle; but all three systems have to interact. In any scenario, the growing follicle has a critical role: it matures the lining, provides the appropriate feedback to the hypothalamus and pituitary, and modifies the mucus changes at the cervix. Two sex hormones play a role in the control of the menstrual cycle: estradiol and progesterone. While estrogen peaks twice, during follicular growth and during the luteal phase, progesterone remains virtually absent prior to ovulation, but becomes critical in the luteal phase and during pregnancy. Many tests for ovulation check for the presence of progesterone. These sex hormones come under the influence of the pituitary gland, and both FSH and LH play necessary roles. FSH stimulates immature follicles in the ovaries to grow. LH triggers ovulation. The gonadotropin-releasing hormone of the hypothalamus controls the pituitary, yet both the pituitary and the hypothalamus receive feedback from the follicle. After ovulation the corpus luteum — which develops from the burst follicle and remains in the ovary — secretes both estradiol and progesterone. Only if pregnancy occurs do hormones appear in order to suspend the menstrual cycle, while production of estradiol and progesterone continues. Abnormal hormonal regulation leads to disturbance in the menstrual cycle. Some women with neurological conditions experience increased activity of their conditions at about the same time every month. 80 percent of women with epilepsy have more seizures than usual in the phase of their cycle when progresterone declines and estrogen increases. Mice have been used as an experimental system to investigate possible mechanisms by which levels of sex steroid hormones might regulate nervous system function. During the part of the mouse estrous cycle when progesterone is highest, the level of nerve-cell GABA receptor subtype delta was high. Since these GABA receptors are inhibitory, nerve cells with more delta receptors are less likely to fire than cells with lower numbers of delta receptors. During the part of the mouse estrous cycle when estrogen levels are higher than progesterone levels, the number of delta receptors decrease, increasing nerve cell activity, in turn increasing anxiety and seizure susceptibility. (Maguire et al., 2005)

Hidden ovulation

Unlike other species, human women have concealed ovulation. A woman may sense her own ovulation while it may remain indiscernible to others; this is considered to have sociobiological significance. In contrast, other species often signal receptivity through heat. In this context, evidence suggests that women's preferences for men may change during their most fertile days; that is, before and shortly after ovulation. During this time, they may prefer different male scents, more masculine faces, and social presence in males considered as partners. (Gangestad 2004; debated) Women, especially young teens, have been noted to dress more provocatively, to say that they feel sexier, to flirt more, and to be more likely to initiate sexual activity around the time of ovulation than they did at other points in their menstrual cycle. Most of this, especially in younger women, appears to be subconscious.

The ovary as an egg-bank

Evidence suggests that eggs are formed from germ cells early in fetal life. The number is reduced to an estimated 400,000 to 450,000 immature eggs residing in each ovary at puberty. The menstrual cycle, as a biologic event, allows for ovulation of one egg typically each month. Thus over her lifetime a woman will ovulate approximately 400 to 450 times. All the other eggs dissolve by a process called atresia. As a woman's total egg supply is formed in fetal life, to be ovulated decades later, it has been suggested that this long lifetime may make the chromatin of eggs more vulnerable to division problems, breakage, and mutation than the chromatin of sperm, which are produced continuously during a man's reproductive life. This possibility is supported by the observation that fetuses and infants of older mothers have higher rates of chromosome abnormalities than those of older fathers.

The anovulatory menstrual cycle

Not all menstruations result from an ovulatory menstrual cycle. In some women, follicular development may start but not complete, nevertheless estrogens will form and will stimulate the uterine lining. Sooner or later the uterus will shed this lining. As no ovulation and no progesterone involvement occurs, doctors call this type of bleeding an estrogen breakthrough bleeding, and cannot always predict its duration or frequency. Anovulatory bleeding commonly occurs prior to menopause (premenopause) or in women with polycystic ovary syndrome.

Cycle abnormalities

Frequency

The "normal menstrual cycle" occurs every 28 days ± 7 days. The medical term for cycles with intervals of 21 days or fewer is polymenorrhea and, on the other hand, the term for cycles with intervals exceeding 35 days is oligomenorrhea (or amenorrhea if intervals exceed 180 days).

Flow

The normal menstrual flow amounts to 50 ml ± 30 ml. It follows a "crescendo-decrescendo" pattern; that is, it starts at a moderate level, increases somewhat, and then slowly tapers. Sudden heavy flows or amounts in excess of 80 ml (hypermenorrhea or menorrhagia) may stem from hormonal disturbance, uterine abnormalities, including uterine leiomyoma or cancer, and other causes. Doctors call the opposite phenomenon, of bleeding very little, hypomenorrhea.

Duration

The typical woman bleeds ("is on her period") for three to seven days out of each month. Prolonged bleeding (metrorrhagia, also meno-metrorrhagia) no longer shows a clear interval pattern. Dysfunctional uterine bleeding refers to hormonally caused bleeding abnormalities, typically anovulation. All these bleeding abnormalities need medical attention; they may indicate hormone imbalances, uterine fibroids, or other problems. As pregnant patients may bleed, a pregnancy test forms part of the evaluation of abnormal bleeding.

The birth control pill

Estrogens and progesterone-like hormones make up the main active ingredients of birth control pills. Typically they tend to mimic a menstrual cycle in appearance, but to suppress the critical event of the ovulatory cycle, namely ovulation. Normally, a woman takes hormone pills for 21 days, followed by 7 days of non-functional placebo sugar pills or no pills at all; then the cycle starts again. During the 7 placebo days, a withdrawal bleeding occurs; this differs from ordinary menstruation, and skipping the placebos and continuing with the next batch of hormone pills may suppress it. (Two main versions of the pill exist: monophasic and triphasic. With triphasic pills, skipping of the placebos and continuing with the next month's dose can remove the pill's pregnancy protection.) In 2003 the United States Food and Drug Administration (FDA) approved low-dose monophasic birth control pills which induce withdrawal bleedings only every 3 months.

Etymology and the lunar month

The terms "menstruation" and "menses" come from the Latin mensis (month), which in turn relates to the Greek mene (moon) and to the roots of the English words month and moon — reflecting the fact that the moon also takes close to 28 days to revolve around the Earth (actually 27.32 days). The synodical lunar month, the period between two new moons (or full moons), is 29.53 days long. Many women, after a period of not being exposed to artificial nighttime lighting, find their menstrual cycles begin to occur in rhythm with the lunar cycle.

Menstrual products

While some women allow their menses to flow freely or learn to recognise when their menses will flow, most women prefer to use some artifical means to absorb or catch their menses to prevent soiling their clothes. There are a number of different methods used:
- Sanitary towels, sanitary napkins, or pads - Rectangular pieces of material worn in the underpants to absorb menstrual flow, often with "wings," pieces that fold around the panties, or a sticky backing to hold the pad in place. Reusable cloth pads are made of cotton (often organic), terrycloth, or flannel, and may be handsewn (from material or reused old clothes and towels) or storebought. Disposable synthetic pads are made of wood pulp or synthetic products, usually with a plastic lining and bleached.
- Tampons - Disposable wads of treated rayon/cotton blends or all-cotton fleece, usually bleached, that are inserted into the vagina to absorb menstrual flow. Some women also make their own tampons from rolled up cotton strips.
- Menstrual cups - A firm, flexible cup- or bell-shaped device worn inside the vagina to catch menstrual flow. Reusable versions include rubber or silcone cups (like the Keeper, Divacup, [http://www.lunette.fi Lunette] and Mooncup). Disposable versions come in soft plastic cups (like Instead).
- Sea sponges - Reuseable soft sponges from plant-like animals that grow on the ocean floor, worn internally to absorb blood.
- Padettes - Disposable wads of treated rayon/cotton blend fleece that are placed within the inner labia to absorb menstrual flow.
- Padded panties - Reuseable cloth (usually cotton) underwear with extra absorbent layers sewn in to absorb flow.
- Blanket, towel, or "bleeding blankie" - Large reuseable piece of cloth, most often used at night, placed between legs to absorb menstrual flow. Pharmaceutical companies also provide products — commonly Non-steroidal anti-inflammatory drugs (NSAIDs) — to relieve menstrual cramps.

Debate

Much debate centers around which menstrual products to use. The main debate can be summarized as one between the convenience, availability, and general knowledge of disposables versus the environmental, monetary, and potential health benefits of reuseables. A secondary aspect of this is commercial responsibility. Disposable menstrual products compose a large and powerful industry in the West, with a near monopoly on advertising, supermarket shelves, and menstrual education, leading many people to believe that these corporate products are their only options. Many people object to the negative portrayal of menstruation in advertising as shameful, unnatural, stinking, and hindering. In contrast, the reuseable menstrual products industry is composed mostly of small, independent, and woman-owned, woman-positive businesses. Finally, some believe that the disposable menstrual products industry is imperialist, forcing or coercing women of other cultures to leave their resueable, inexpensive or free menstrual products to become consumers of disposables. A summary of the main issues of debate: ; Environmental waste : Tampons, pads, disposable cups and their packaging generate tons of bulky waste per year, much of which is not biodegradable. ; Cost : Many disposables have a cheaper upfront cost than reuseables, but over time (a period of a few months), this cost is recouped many times over from savings on reuseables. Many reuseables can also be made for free from old clothes or scraps of cloth. ; Health concerns : 1. Bleaching - Many women object to the chlorine bleaching of disposable menstrual products, which leaves trace amounts of dioxin, a carcinogen, in them. 2. Scents and deodorizers - Chemical scents and deodorizers can cause rashes, irritation, and allergic reactions. They can upset the pH balance of the vagina and cause yeast infections. ; Health concerns specific to tampons : Toxic Shock Syndrome is caused by Staphylococcus aureus, which can thrive the environment found in tampon fibers. It is important to remember that TSS is very rare, with only approx. 40 cases per year in the UK. Tampon-associated TSS is not a staph infection. It is caused when the bacteria release a protein called toxic shock syndrome toxin (TSST). TSST is absorbed into the body where it acts as a toxin. Toxic Shock Syndrome can, and does, cause death. TSS can be avoided by using the least absorbent tampon possible for one's flow, and changing tampons at least every 8 hours, or by avoiding tampons altogether. This may apply to sea sponges also, though no cases of TSS with sea sponge use have been reported.

Culture and menstruation

Mysticism

Mystics have sometimes elaborated "equivalencies", analogising the waxing and waning of the moon with influences on human menstruation. In this spiritual, moon goddess, or astrological context some women call menstruation their "moontime". Some ancient views also regarded menstruation as a cleansing of the body: compare bloodletting as a major medical treatment of pre-modern times.

Religion

Some religions consider women "unclean" during menstruation.

Islam on menstruation

The Islamic world considers a woman "not in a state to have intercourse" during menstruation. A verse from the Qur'an (with parenthesised interpolations by Dr. Muhammed Muhsin Khan) affirms this:

"They ask you concerning menstruation. Say: that is an Adha (a harmful thing for a husband to have sexual intercourse with his wife while she is having her menses), therefore keep away from women during menses and go not unto them till they have purified (from menses and have taken a bath). And when they have purified themselves, then go in unto them as Allâh has ordained for you. Truly, Allâh loves those who turn unto Him in repentance and loves those who purify themselves (by taking a bath and cleaning and washing thoroughly their private parts, bodies, for their prayers, etc.)." (Al-Baqarah 2:222)

See [http://63.175.194.25/index.php?ln=eng&ds=qa&lv=browse&QR=43028&dgn=4 an Islamic review] on the subject.

Judaism on menstruation

A ritual exclusion applies to a woman while menstruating and for about a week thereafter, until she immerses herself in a mikvah (ritual bath).

Menstruation in other mammals

A regular menstrual cycle as described here only occurs in the great apes. Menstrual cycles vary in length from an average of 29 days in orangutans to an average of 37 days in chimpanzees. Females of other mammalian species go through certain episodes called "estrus" or "heat" in each breeding season. During these times, ovulation occurs and females become receptive to mating, a fact advertised to males in some way. If no fertilisation takes place, the uterus reabsorbs the endometrium: no menstrual bleeding occurs. Significant differences exist between the estrus and the menstrual cycle. Some animals, such as domestic cats and dogs do produce a very short and mild menstural flow, however due to its small amount (and personal cleanliness in cats) it passes pet owners largely unnoticed.

References

- K. Stern and M. K. McClintock: "[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9515961 Regulation of ovulation by human pheromones.]" Nature, 392 (1998), pages 177 – 179.
- Gangestad et al.: "[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15016293 Women's preferences for male behavioral displays change across the menstrual cycle.]" Psychological Science, March 2004, vol. 15, no. 3, pages 203 - 207
-

Notes

# "[http://www.4woman.gov/faq/menstru.htm#6 At what age does a girl get her first period?]," from Menstruation and the Menstrual Cycle, National Women's Health Information Center (accessed June 11, 2005). # Ibid., "[http://www.4woman.gov/faq/menstru.htm#4 What is a typical menstrual period like?]" (accessed June 11, 2005). # "Lower olfactory threshold during the ovulatory phase of the menstrual cycle" by E. Navarrete-Palacios, R. Hudson, G. Reyes-Guerrero and R. Guevara-Guzman in Biol Psychol. (2003) volume 63 page 269-279 . # M. Ball, "A prospective field trial of the Ovulation Method", European Journal of Obstetrical and Gynaecological Reproductive Biology, 6/2, 63-6, 1976. (Summarized at [http://www.woomb.org/bom/trials/index.html Trials of the Billings Ovulation Method] accessed November 3, 2005) # "Medical Microbiology" 4th ed. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&term=toxic+shock+syndrome+AND+mmed%5Bbook%5D+AND+147524%5Buid%5D&rid=mmed.section.769#775 Online textbook] Samule Baron, editor. (1996) Published by University of Texas Medical Branch; Galveston (TX)

External links

- Harry Finley: Online museum of menstruation and women's health, http://mum.org/
- [http://www.powerhousemuseum.com/rags/ The rags: paraphernalia of menstruation]
- Menstral - track your periods and fertility on your cell phone: http://procod.com/menstral/
- [http://www.bloodays.com/ Bloodays - Software for tracking ovulation, natural conception and contraceptions]
- [http://www.ovusoft.com/ Ovusoft - Software for tracking ovulation and other cycle-related events, community message boards]
- Track your likely ovulatory date with this free [http://www.ovulation-calendar.net/ Ovulation Calendar]
- [http://www.perimon.com/ Free Software to watch the menstrual cycle etc.]
- Mencal - calendar software for UNIX-style operating systems with the ability to highlight repeating cycles: http://kyberdigi.cz/projects/mencal/english.html
- Leslie Botha-Williams, Women's Health Educator: A Woman's Guide to Understanding Her Hormone Cycle, http://www.holyhormones.com
- [http://63.175.194.25/index.php?ln=eng&ds=qa&lv=browse&QR=43028&dgn=4 An Islamic answer for the ruling of women menstruating]
- Menstrual Suppression With Birth Control Pills http://www.noperiod.com
- [http://www.livejournal.com/users/incendiaryfs/204904.html Love Your Blood: An info-zine on menstrual products and their alternatives]
- [http://www.seac.org/tampons/ Tampaction] and [http://bloodsisters.org/bloodsisters/ The Bloodsisters Project]- Menstrual activism against chlorine bleaching, excessive packaging, and negative attitudes toward menstruation in the West
- [http://www.scarleteen.com/body/ontherag.html On The Rag: Everything you need to know about your fertility cycles and menstruation...period] - Article on the menstrual cycle by notable sex activist and educator Heather Corinna
- [http://www.scarleteen.com/pink/washable.html Eight Myths About Washable Menstrual Pads Dispelled] Category:Reproductive system Category:Gynecology ja:月経

Vagina

The vagina, (from the Latin for "sheath" or "scabbard" ) is the 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 oviduct.

Human vagina

Anatomy

The human vagina is an elastic muscular tube about 4 inches (100 mm) long and 1 inch (25 mm) in diameter that connects the vulva at the outside to the cervix of the uterus at the inside. If the woman stands upright, the vaginal tube points in an upward-backward direction and forms an angle of slightly more than 45 degrees with the uterus. The vaginal opening is at the back (caudal) end of the vulva, behind the opening of the urethra. Above the vagina is Mons Veneris.The inside of the vagina is usually pink, as with all internal mucous membranes in mammals. (In common speech, the term "vagina" is often used improperly to refer to the vulva or female genitals generally; strictly speaking the vagina is a specific internal structure and the vulva is the exterior genitalia only. Calling the vulva the vagina is akin to calling the mouth the throat.) Length, width and shape of the vagina may vary. When a woman gives birth and during sexual intercourse, the vagina widens and lengthens up to 2-3 times. Vaginal lubrication is provided by glands near the vaginal opening and the cervix and also seeps through the vaginal wall (which does not contain any glands). The hymen—a membrane situated behind the urethral opening—partially covers the vagina in many organisms, including some human females, from birth until it is ruptured by sexual intercourse, or by any number of other activities including medical examinations, injury, certain types of exercise, introduction of a foreign object, etc.

Functions of the vagina

From a biological perspective, the vagina performs the following functions:
- Providing a path for menstrual fluids to leave the body.
- Giving birth
- Admitting the male penis for sexual intercourse

Sexual intercourse

The vagina admits the male penis for sexual intercourse and ultimately male sperm for the fertilization of ova for reproduction. Heterosexual post-pubescent males are generally sexually attracted to the human female vagina and the resulting penile erection from such arousal facilitates vaginal penetration. (See: sexual intercourse). The concentration of nerve endings particularly close to the mouth of the vagina causes pleasure to be experienced during sexual activity. The opening of the vagina is home to the clitoris, which is located at the anterior of the vaginal opening; for most women, the clitoris is the main source of sexual pleasure (although it can be too sensitive for direct stimulation in some women). Some women have a very sensitive erogenous zone called "the G-spot" inside their vagina (in the anterior of the vagina, about five cm. in from the entrance), which can produce very intense orgasms if stimulated properly, possibly responsible for the disputed female ejaculation. Not all women have a g-spot that is responsive to stimulation, however.

Giving birth

During live birth, the vagina provides the route to deliver the fetus from the uterus to its independent life outside the body of the mother. During birth, the vagina is often referred to as the birth canal.

Menstruation

The vagina provides a path for menstrual fluids to leave the body. In Western societies, tampons and sanitary towels may be used to absorb these fluids.

Sexual health and hygiene

Other than the penis, fingers or sexual devices, many women insert tampons during menstruation. These must be regularly changed - every four hours at most. Other objects inserted include diaphragms (placed against the cervix, blocking it from sperm), spermicidal cream and lubicrant. Additionally, some women use vaginal douches, which serve to cleanse the vagina with a gentle soap intended to remove odor. These days, such treatment is advised against by doctors, as it may upset the balance of bacteria in the vagina, rather than helping it. Thus, the vagina itself needs no particular treatment in the name of basic hygiene. The vagina is examined during gynecological exams, often using an instrument called a speculum, which keeps the vagina open for visual inspection or taking of samples (see pap smear). Various disorders can affect the vagina, including vaginal cancer and yeast infections. See vulvovaginal health.

The vagina and popular culture

Sexual organs being stimagtised in practically all human cultures, it is not surprising that Western society treats the subject as somewhat taboo. A one-person play by Eve Ensler known as The Vagina Monologues was a rare example of the word appearing in mainstream culture. The popular TV series Sex and the City contains many discussions about the vagina and its health.

External links

- [http://www.the-clitoris.com/ The-Clitoris.com]
- [http://www.scarleteen.com/body/female_anatomy.html Pink Parts] - "Walk through" of female sexual anatomy by noted sex activist and educator Heather Corinna (illustrations; no explicit photos) Category:Reproductive system Category:Gynecology ja:膣 simple:Vagina

Menstruation

The normal menstrual cycle in humans

Menstruation

Follicular phase

Ovulation

Luteal phase

Menstrual symptoms

The fertile window

Hormonal control

Hidden ovulation

The ovary as an egg-bank

The anovulatory menstrual cycle

Cycle abnormalities

Frequency

Flow

Duration

The birth control pill

Etymology and the lunar month

Menstrual products

Debate

Culture and menstruation

Mysticism

Religion

Some religions consider women "unclean" during menstruation.

Islam on menstruation

The Islamic world considers a woman "not in a state to have intercourse" during menstruation. A verse from the Qur'an (with parenthesised interpolations by Dr. Muhammed Muhsin Khan) affirms this:

"They ask you concerning menstruation. Say: that is an Adha (a harmful thing for a husband to have sexual intercourse with his wife while she is having her menses), therefore keep away from women during menses and go not unto them till they have purified (from menses and have taken a bath). And when they have purified themselves, then go in unto them as Allâh has ordained for you. Truly, Allâh loves those who turn unto Him in repentance and loves those who purify themselves (by taking a bath and cleaning and washing thoroughly their private parts, bodies, for their prayers, etc.)." (Al-Baqarah 2:222)

See [http://63.175.194.25/index.php?ln=eng&ds=qa&lv=browse&QR=43028&dgn=4 an Islamic review] on the subject.

Judaism on menstruation

A ritual exclusion applies to a woman while menstruating and for about a week thereafter, until she immerses herself in a mikvah (ritual bath).

Menstruation in other mammals

References

Notes

External links

Gonadotropin-releasing hormone

Gonadotropin releasing hormone (GnRH) is a peptide hormone responsible for the release of FSH and LH from the anterior pituitary. GnRH is synthesized and released by the hypothalamus.

Gene

The gene for the GnRH precursor is located on chromosome 8. This precursor contains 92 amino acids and is processed to GnRH, a decapeptide (10 amino acids).

Structure

The identity of GnRH was clarified by the 1977 Nobel Laureates Roger Guillemin and Andrew V. Schally: pyroGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly CONH2.

GnRH as a neurohormone

GnRH is considered a neurohormone, a hormone produced in a specific neural cell and released at its neural terminal. A key area for production of GnRH in the hypothalamus is the preoptic area, that contains most of the GnRH secreting neurons. GnRH is secreted in the portal bloodstream at the level of the median eminence, the gonadotropes, and activates receptors in the cell wall. GnRH is degradated by proteolysis within a few minutes.

Control of FSH and LH

In the pituitary GnRH stimulates synthesis and release of FSH and LH, a process that is controlled by the frequency and amplitude of GnRH pulses, as well as the feedback of androgens and estrogens. Sex differences exist in the GnRH secretion in male and female: in particular, in the male GnRH is secreted in pulses at a constant frequency, while in the female the frequency of the pulses varies during the menstrual cycle and a surge of GnRH is observed before the ovulation. The pulsatility of GnRH secretion has been seen in all vertebrates, and it is necessary to ensure a correct reproductive function. Thus a single hormone, GnRH, controls a complex process of follicular growth, ovulation, and corpus luteum maintenance in the female, and spermatogenesis in the male.

Activity

GnRH activity is very low during childhood. During the reproductive years pulse activity is critical for successful reproductive function as controlled by feedback loops. However, once a pregnancy is established GnRH activity is not required. Pulse activity can be disrupted by hypothalamic-pituitary disease, either dysfunction (i.e hypothalamic suppression) or organic lesions (trauma, tumor). Elevated prolactin levels decrease GnRH activity. In contrast hyperinsulinemia increases pulse activity leading to disordery LH and FSH activity as seen in PCOS. GnRH formation is congenitally absent in Kallmann syndrome. Dopamine appears to decrease GnRH activity.

GnRH in other organs

GnRH is found in organs outside of the hypothalamus and pituitary and its role in other life processes is poorly understood. For instance, there is likely to be a role for GnRH in the placenta and in the gonads.

Medication

GnRH is available as gonadorelin hydrochloride (Factrel) for injectable use. Studies have described it being used via an infusion pump system to induce ovulation in patients with hypothalamic hypogonadism.

Agonists and antagonists

While GnRH has been synthesized and become available, its short half life requires infusion pumps for its clinical use. Modifications of the decapeptide structure of GnRH have led to analog medications that either stimulate (GnRH agonists) or suppress (GnRH antagonists) the gonadotropins. Importantly, through