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Decidua

Decidua

Decidua is the term for the uterine lining (endometrium) during a pregnancy. It is formed under the influence of progesterone and serves to support and interact with the gestation. The decidua represents the maternal portion of the placenta.

Etymology

The word comes from the Latin deciduus, meaning falling off or shedding.

Background

After ovulation, in mammals, the endometrial lining becomes transformed into a secretory lining in preparation to accept the embryo. Without implantation the secretory lining will be absorbed (estrous cycle) or shed (menstrual cycle). With implantation the lining now termed decidua evolves further during the pregnancy. The decidua is shed during the parturition process.

Structure

Different layers of the deciduas have been described, a compact outer layer (stratum compactum), an intermediate layer (stratum spongiosum), and a boundary layer adjacent to the myometrium. That part of the deciduas that interacts with the trophoblast is the decidua vera (“true decidua”), the remainder of the decidua is termed the decidua parietalis. The decidua has a histologically distinct appearance displaying large polygonal decidua cells in the stroma. Vascularity is enhanced. Its leukocyte population is distinct with the presence of large endometrial granular leukocytes being predominant, while polynuclear leukocytes and B-cells are scant. The border to the trophoblast is called Nitabuch’s layer.

Role

As the maternal interface to the embryo the decidua participates in the exchanges of nutrition, gas, and waste with the gestation. It also protects the pregnancy from the maternal immune system. Further, the decidua has to allow a very controlled invasion of the trophoblast.

Hormone production

The decidua secretes hormones, growth factors, and cytokines. It has receptors for estrogen, progesterone, growth hormone, and others. Among its products are hormones commonly associated with other organs such as cortisol, CRF, GnRH, prolactin, and relaxin. Decidual prolactin is not under dopaminergic control. Pregnancy protein 14 (PP-14) appears to be a specific product of the secretory and decidual lining. Other factors released include interleukin-15, vascular endothelial growth factor (VEGF), and insulin-like growth factor binding proteins. A reasonable understanding of the role and interplay of these hormones and factors has not been evolved.

Other

- In case of an extrauterine pregnancy, the endometrium nevertheless becomes decidualized. A women may shed the lining in the form of a decidual cast which may be mistaken as a miscarriage, when, in fact, the ectopic still persists.
- A decidual reaction can be observed in tissue of the peritoneum and ovary during a pregnancy and represents a response of stromal tissue to progesterone.

External links

#[http://www-medlib.med.utah.edu/WebPath/PLACHTML/PLAC094.html Histologic picture] #[http://education.yahoo.com/reference/gray/subjects/subject?id=12 Gray’s anatomy] Category:Anatomy Category:Obstetrics

Uterus

The uterus or womb is the major female reproductive organ of most mammals, including humans. One end, the cervix, opens into the vagina; the other is connected on both sides to the fallopian tubes. In mammals, the four main forms in which it is found are: bipartite, as in cows; bicornuate, as in pigs; simplex, as with the pear-shaped one found in humans and horses; and duplex, found in rabbits.

Development

The bilateral Müllerian ducts form during early fetal life. In males, MIF secreted from the testes leads to their regression. In females these ducts give rise to the Fallopian tubes and the uterus. In humans the lower segments of the two ducts fuse to form a single uterus, however, in cases of uterine malformations this development may be disturbed. The different uterine forms in different mammals are due to various degrees of fusion of the two Müllerian ducts.

Anatomy

The uterus is located in the pelvis immediately dorsal (and usually somewhat rostral) to the urinary bladder and ventral to the rectum. It is held in place by eight ligaments (one anterior; one posterior; two lateral or broad; two uterosacral; and two round ligaments). It is usually slightly anteverted (tipped forward) but is sometimes retroverted (tipped backwards). Outside of pregnancy, its size is several centimeters in diameter. The uterus mostly consists of muscle, known as myometrium. The innermost layer of myometrium is known as the junctional zone, which becomes thickened in adenomyosis. The lining of the uterine cavity is called the endometrium. In most mammals, including humans, the endometrium builds a lining periodically which, if no pregnancy occurs, is shed or reabsorbed. Shedding of the endometrial lining in humans is responsible for menstrual bleeding (known colloquially as a woman's "period") throughout the fertile years of a female and for some time beyond. In other mammals there may be cycles set as widely apart as six months or as frequently as a few days. The loose surrounding tissue is called the parametrium.

Function

The main function of the uterus is to accept a fertilized ovum which becomes implanted into the endometrium, and derives nourishment from blood vessels which develop exclusively for this purpose. The fertilized ovum becomes an embryo, develops into a fetus and gestates until childbirth. Due to anatomical barriers such as the pelvis, the uterus is pushed partially into the abdomen due to its expansion during pregnancy. Even in pregnancy the mass of a human uterus amounts to only about a kilogram (2.2 pounds).

Pathology

Some pathological states include:
- prolapse of the uterus
- carcinoma of the cervix - malignant neoplasm
- carcinoma of the uterus - malignant neoplasm
- ectopic pregnancy
- fibroids - benign neoplasms
- adenomyosis - ectopic growth of endometrial tissue within the myometrium

Terminology

The term uterus is commonly used within the medical and related professions, whilst the term womb is in more common usage.

External links

- [http://education.yahoo.com/reference/gray/subjects/subject?id=268 Gray's]
- [http://bioweb.wku.edu/courses/Biol131/images/uterus.jpg Illustration] Category:Pelvis Category:Reproductive system zh-min-nan:Seⁿ-kiáⁿ-tē ja:子宮

Endometrium

The endometrium is the inner uterine membrane in mammals which is developed in preparation for the implantation of a fertilized egg upon its arrival into the uterus. It grows to be rich in glands and blood vessels, which are eventually to be connected to by the pregnancy, forming the placenta through which the embryo, as it becomes a fetus and eventually gestates fully, receives oxygen and is nourished. The endometrial lining undergoes cyclic regeneration. Most mammals are subject to an estrous cycle while humans and the great apes display the menstrual cycle. In either situation the endometrium proliferates initially under the influence of estrogen. Once ovulation occurs, in addition to estrogen the ovary will also start to produce progesterone and thereby change the proliferative pattern of the endometrium to a secretory lining. In time the secretory lining provides a hospitable environment to one or more fertilized eggs. If no fertilized egg is detected, the progesterone level drops and the endometrial lining is either reabsorbed (estrous cycle) or shed (menstrual cycle). In the latter, the process of shedding involves the breaking down of the lining, tearing small connective blood vessels, and the loss of the tissue and blood which had constituted it through the vagina, over a series of days. This may be accompanied by some uterine contractions to help expel the menstrual endometrium. In case of implantation, however, the endometrial lining does not get absorbed or shed, but remains as decidua, provides support and protection for the gestation, and becomes part of the placenta. If there is inadequate stimulation of the lining due to lack of hormones, the endometrium remains thin and inactive. In humans this will result in amenorrhea. The lining after the menopause is often described to be atrophic. In contrast, endometrium that is chronically exposed to estrogens, but not to progesterone, may become hyperplastic. In humans, the cycle of building and shedding the endometrial lining is 28 days long on average, though it varies among individuals. The endometrium develops at different rates in different mammals. Its formation is sometimes affected by seasons, climate, stress and other factors. The endometrium itself produces certain hormones at different points in the cycle affecting other portions of the reproductive system. More about the patterns of endometrial growth in different mammals can be found in the article about the estrous cycle.

Other

Growth of the endometrium into the muscle layer of the uterus (myometrium) is seen in adenomyosis. Growth of endometrial tissue outside the uterus is a pathological condition known as endometriosis. Endometrial cancer is the most common cancer of the human female genital tract.

Pregnancy

:For a broader view of pregnancy in mammals see mammalian pregnancy. For the medicine of pregnancy, see Obstetrics. Obstetrics Pregnancy is the carrying of one or more embryos or foeti by female mammals, including humans, inside their bodies. In a pregnancy there can be multiple gestations (for example, in the case of twins, or triplets). Human pregnancy is the most studied of all mammalian pregnancies. Human pregnancy lasts approximately 40 weeks between the time of the last menstrual cycle and birth (38 weeks from fertilisation). The medical term for a pregnant woman is "genetalian," just as the medical term for the unborn human is an embryo (early weeks) and then "foetus" (until birth). A woman who is pregnant for the first time is known as a primigravidanite or gravida 1: a woman who has never been pregnant is known as a gravida 0; similarly, the terms para 0 and para 1 are used for the number of times a woman has given birth. In many societies' medical and legal definitions, human pregnancy is arbitrarily divided into three trimester periods, as a means to simplify reference to the different stages of fetal development. The first trimester period carries the highest risk of miscarriage (natural death of embryo or fetus), while during the second trimester the development of the fetus can start to be monitored and diagnosed. The third trimester marks the beginning of viability, which means the fetus can survive if an early natural or induced birth occurs. Because of the possible viability of developed fetus, cultural and legal definitions of life often consider a fetus in the third trimester to be a distinct living person. :See also Pregnancy terms and definitions
Detection and dating
Pregnancy terms and definitions The beginning of pregnancy may be detected in a number of ways, including various pregnancy tests which detect hormones generated by the newly-formed placenta. Clinical blood and urine tests can detect pregnancy as early as 6-8 days after date of conception. Home pregnancy tests are personal urine tests, which normally can't detect a pregnancy until at least 12-15 days after conception. Both clinical and home tests can only detect the state of pregnancy, and cannot detect the actual date of conception. Home pregnancy test In practice, for the purpose of giving a date for a conception (i.e. an "age" for an embryo), doctors typically date the pregnancy by "menstrual date," based on the first day of a woman's last menstrual period, as the woman reports it. Unless a woman's recent sexual activity has been limited, the exact date of conception or implantation are unknown. And absent any symptoms of morning sickness, the only visible sign of a pregnancy is often an interruption of her normal monthly menstruation cycle, (i.e. a "late period"). Hence, the "menstrual date" is simply a common educated estimate for the age of a fetus, which is an average of two weeks later than conception, (the margin of error considers 0 to 30 days after last menstruation, hence a 14 day average). The term "conception date" may sometimes be used when that date is more certain, though even medical professionals can be imprecise with their use of the two distinct terms. An unknown date for conception means that in practice the distinction between embryo and fetus is a clinical one only, and not used as to refer to stages of development of a particular pregnancy. margin of error There are likewise finer distinctions between the concepts of fertilization (conception) and the actual state of pregnancy. In a normal pregnancy, the fertilization of the egg usually will have occurred in the Fallopian tubes or in the uterus. (In women with fertility problems, an egg may become fertilized yet fail to become implanted in the uterus.) If the pregnancy is the result of in-vitro fertilization the fertilization will have occurred in a Petri dish, after which "pregnancy" begins when one or more zygotes implants after being transferred by a physician in the woman's uterus. In the context of political debates regarding a proper definition of life, the terminology of pregnancy can be confusing. Because precise assessment of a pregnancy as being at the "embryo" or "fetus" stage is usually undeterminable, the terms (though more clinically precise) are less commonly used than terms like "baby" or "child." The medically and politically neutral term which remains is simply "pregnancy," though this can be problematic as it only refers indirectly to the embryo or fetus. In the context of personal treatment, bedside manner generally dictates that doctors make sparse use of clinical language like "fetus" and "embryo," and instead simply refer to the developing child as a "baby." progesterone
Timeline of a typical pregnancy
Pregnancy is typically broken into three periods, or trimesters, each of about three months. While there are no hard and fast rules, these distinctions are useful in describing the changes that take place over time.
First trimester

Fertilization
progesterone progesterone Before pregnancy begins, a female oocyte (egg) must be fertilized, by male sperm in a process referred to in medicine as "fertilization," or commonly as "conception." Pregnancy is usually dated as beginning on the first day of a woman's last menstrual period. This date is used to estimate an EDD, or Estimated Date of Delivery. Traditionally (according to Naegele's Rule, which is used to calculate the estimated date of delivery (EDD)), a human pregnancy is considered to last approximately 40 weeks (280 days) from the last menstrual period (LMP), or 37 weeks (259 days) from the date of conception. However, a pregnancy is considered to have reached term between 37 and 43 weeks. Babies born before the 37 week mark are considered premature, while babies born after the 43 week mark are considered postmature. postmature However, the average length of pregnancy depends on ethnic background of the mother (Caucasian women are more likely to have a longer pregnancy than other women) and if it is a first pregnancy (which tend to last longer than subsequent pregnancies). For example, a Caucasian woman's first pregnancy lasts an average 274 days from conception (288 days from the last menstrual period). An accurate date of conception is important, because it is used in calculating the results of various prenatal tests (for example, in the triple screen test). A decision may be made to induce labour if a baby is perceived to be overdue. Due dates are only a rough estimate, and the process of accurately dating a pregnancy is complicated by the fact that not all women have 28 day menstrual cycles, or ovulate on the 14th day following their last menstrual period. Approximately 3.6% of all mothers deliver on the due date predicted by LMP, and only 4.7% give birth on the day predicted by ultrasound.
Implantation
In medicine, pregnancy is defined as beginning when the developing embryo becomes implanted into the endometrial lining of a woman's uterus. The outer layers of the embryo grow and form a placenta, for the purpose of receiving essential nutrients through the uterus wall. The umbilical cord in a newborn child signifies the remnants of the connection to the placenta. The developing baby undergoes tremendous growth and changes during the process of embryonic and fetal development. Morning sickness aflicts about half of all pregnant women, typically only in the first trimester.
Second trimester
Morning sickness Most women feel more energised in this period, and begin to seriously put on weight. The first movement of the baby, often referred to as "quickening", can be felt, as the baby begins to form into a recognisable shape.
Third trimester
Final weight gain takes place, and the baby begins to move regularly. This can be uncomfortable, causing symptoms like weak bladder control and back-ache.
Medical aspects of pregnancy
Diagnostic criteria are: In a woman who has regular menstrual cycles and is sexually active, a period delayed by a few days or weeks is suggestive of pregnancy; elevated B-hcG to around 100,000 mIU/mL by 10 weeks of gestation.
Birth
Morning sickness Childbirth is the process in which the baby is born. It is considered by many to be the beginning of a person's life, where age is defined relative to this event in most cultures. A woman is considered to be in labour when she begins experiencing regular painful uterine contractions, accompanied by changes of her cervix — primarily effacement and dilation. While childbirth is widely experienced as painful, some women do report painless labours.
Postnatal Period
For topics following on from a successful pregnancy and birth, see:
- Breastfeeding
- Child development
Terms and definitions

Technical

- zygote - from fertilization until second cell division
- embryo - conceptus between time of fertilization to 10 weeks of gestation
- fetus - from 10 weeks of gestation to time of birth
- FASD - Fetal Alcohol Spectrum Disorder, a clinical term for the effects alcohol can have on the developing fetus
- gestational age - time from last menstrual period (LMP) up to present
- gravidity (G) - number of times a woman has been pregnant
- infant - time of birth to 1 year of age
- viability - minimum age for fetus survival, ca. third trimester
- previable infant - delivered prior to 24 weeks
- preterm infant - delivered between 24-37 weeks
- term infant - delivered between 37-42 weeks
- first trimester - up to 14 weeks of gestation
- second trimester - 14 to 28 weeks of gestation
- third trimester - 28 weeks to delivery
- parity (P) - number of pregnancies with a birth beyond 20 weeks GA or an infant weighing more than 500 g
- Ga Pw-x-y-z - a = number of pregnancies, w = number of term births, x = number of preterm births, y = number of miscarriages, z = number of living children; for example, G4P1-2-1-3 means the woman had a total of 4 pregnancies, of which 1 is of term, 2 are preterm, 1 miscarriage, and 3 total living children (1 term + 2 preterm).
Colloquial
There are a number of colloquialisms for pregnancy, usually regional. The action of impregnating a woman or girl is called 'knocking (her) up' in Canada and some parts of the U.S., and the state of being pregnant 'knocked-up'. The term 'lady-in-waiting', meaning a pregnant mother, is used broadly in the U.S. The word 'gone' or 'along' is used to represent gestational time, e.g. 'she's really far gone' or 'about 6 weeks gone' or 'six months along'. In the southern U.S. the euphemism of a water well is occasionally used to represent pregnancy (e.g. 'drink out of the well', to become pregnant), and a baby almost ready to be delivered is 'on his/her road'. Eastern Seaboard slang describes the mother as being 'in a fix' or, occasionally, 'preggers'; the Southern U.S. equivalent is 'in the family way'. An alternate term not slang or colloquial is 'with child', now restricted mainly to England. 'Having a bun in the oven' is another frequently used phrase to indicate that a woman is pregnant.
See also

- Abortion
- Lamaze
- Obstetrics
- Contraception
- Twin and Multiple birth
- Teenage pregnancy
- Pregnancy discrimination
- Low birth weight paradox
- Pregnancy in science fiction
- Melasma
- Wrongful abortion
- False pregnancy
- Simulated pregnancy
Reference

- Mittendorf R, Williams MA, Berkey CS, Cotter PF. The length of uncomplicated human gestation. Obstet Gynecol 1990;75:929-32. PMID 2342739.
External links

- [http://www.mayoclinic.com/health/pregnancy/HQ00451 Early pregnancy: Morning sickness, fatigue and other common symptoms, from MayoClinic.com]
- [http://www.visembryo.com/ The visible embryo]
- [http://www.merck.com/mrkshared/mmanual/section18/chapter249/249a.jsp Normal Pregnancy, Labor, And Delivery (Merck Manual)]
- Alan Guttmacher Institute [http://www.agi-usa.org/pubs/tgr/08/2/gr080207.html (2005) The Implications of Defining When a Woman Is Pregnant discussion of the political and legal background.
- [http://www.normalbirth.lamaze.org Lamaze Institute for Normal Birth], an advocacy site for "natural" childbirth.
- [http://www.chabad.org/library/article.asp?AID=72141 Jewish customs for conduct during Pregnancy and Birth] chabad.org Category:Midwifery Category:Obstetrics Category:Women Category:Fertility ko:임신 ja:妊娠

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

Ovulation

Ovulation is the process in the menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum (also known as an oocyte, female gamete, or casually, an egg) that participates in reproduction. Ovulation also occurs in the estrous cycle of animals, which differs in many fundamental ways to the menstrual cycle. Note: This article deals primarily with human ovulation; nonhuman animal ovulation is touched on briefly at the conclusion.

Overview

In humans, the period when ovulation occurs is called the ovulatory phase, and it occupies the fourteenth day of an idealized twenty-eight day menstrual cycle. Because of the variable nature of the menstrual cycle in vivo, however, normal ovulation can occur as early as day 8 or as late as day 20 and beyond. A woman with a particularly short cycle will ovulate earlier while a woman with a long cycle will ovulate later. In humans, concealed ovulation means that the female shows few visible signs of being fertile, compared to most species. There are evolutionary analyses of how this could evolve in terms of evolutionary game theory. Before ovulation, the ovarian follicle will undergo a series of transformations that are necessary for the ovum to survive afterwards. This process is called cumulus expansion. After this is done, a hole called the stigma will form in the follicle, and the ovum will leave the follicle through this hole. It will then enter the fallopian tubes and travel toward the uterus, implanting there if fertilized or degrading after 24 hours if not. The ovulatory phase is preceded by the follicular phase, where a immature follicle-encased ovum completes growing, and followed by the luteal phase, where the uterus is prepared to receive the fertilized ovum. The complete process of follicle growth leading up to ovulation is known as folliculogenesis. Scientific investigations like [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12853171&query_hl=3] have indicated that the olfactory acuity or the sense of smell is greatest during ovulation in women.

A closer look at the process

Strictly defined, the ovulatory phase spans the period of hormonal elevation in the menstrual cycle. The process requires a maximum of thirty-six hours to complete, and it is arbitrarily separated into three phases: periovulatory, ovulatory, and postovulatory.

Prerequisite events

smell Main page: folliculogenesis Through a process that takes approximately 375 days, or thirteen menstrual cycles, a large group of undeveloped primordial follicles dormant in the ovary is grown and progressively weaned into one preovulatory follicle. Histologically, the preovulatory follicle (also called a mature Graffian follicle or mature tertiary follicle) contains an oocyte arrested in prophase of meiosis I surrounded by a layer corona radiata granulosa cells, a layer of mural granulosa cells, a protective basal lamina, and a network of blood-carrying capillary vessels sandwiched between a layer of theca interna and theca externa cells. A large sac of fluid called the antrum predominates in the follicle. A "bridge" of cumulus oophorous granulosa cells (or simply cumulus cells) connects the corona-ovum complex to the mural granulosa cells. Simply stated, the granulosa cells engage in bidirectional messenging with the theca cells and the oocyte to facilitate follicular function. Research is elucidating the specific factors used in follicular messenging at a rapid pace, but such discussion is beyond the scope of this article. By the action of luteinizing hormone (LH), the preovulatory follicle's theca cells secrete androstenedione that is aromatized by mural granulosa cells into estradiol, a type of estrogen. High levels of estrogen have a stimulatory effect on hypothalamus gonadotropin-releasing hormone (GnRH) that in turn stimulates the expression of pituitary LH and follicle stimulating hormone (FSH). The building concentrations of LH and FSH marks the beginning of the periovulatory phase.

Periovulatory phase

For ovulation to be successful, the ovum must be supported by both the corona radiata and cumulus oophorous granulosa cells. The latter undergo a period of proliferation and mucification known as cumulus expansion. Mucification refers to the secretion of a hyaluronic acid-rich cocktail that disperses and suspends the cumulus cell network in a sticky matrix around the ovum. This network stays with the ovum after ovulation and have been shown to be necessary for fertilization. An increase in cumulus cell number causes a concomitant increase in antrum fluid volume that can swell the follicle to over 20mm in diameter. It forms a pronounced bulge at the surface of the ovary called the blister.

Ovulatory phase

Through a signal transduction cascade kicked off by LH, proteolytic enzymes are secreted by the follicle that degrade the follicular tissue at the site of the blister, forming a hole called the stigma. The ovum-cumulus complex leaves the ruptured follicle and out into the peritoneal cavity through the stigma, where it is caught by the fimbriae at the end of the fallopian tube (also called the oviduct). After entering the oviduct, the ovum-cumulus complex is pushed along by cilia, beginning its journey toward the uterus. By this time, the oocyte has completed meiosis I, yielding two cells: the larger secondary oocyte that contains all of the cytoplasmic material and a smaller, inactive first polar body. Meiosis II follows at once but will be arrested in the metaphase and will so remain until fertilization. The spindle apparatus of the second meiotic division appears at the time of ovulation. If no fertilization occurs, the oocyte will degenerate approximately twenty-four hours after ovulation. The mucous membrane of the uterus, termed the functionalis, has reached its maximum size, and so have the endometrial glands, although they are still non-secretory.

Postovulatory phase

Main article: corpus luteum The follicle proper has met the end of its lifespan. Without the ovum, the follicle folds inward on itself, transforming into the corpus luteum (pl. corpus lutea), a steriodogenic cluster of cells that produces estrogen and progesterone. These hormones induce the endometrial glands to begin production of the proliferative endometrium, the site of embryonic growth if fertilization occurs. The corpus luteum continues this paracrine action for the remainder of the menstrual cycle, maintaining the endometrium, before disintegrating into scar tissue during menses.

Clinical presentation

The start of ovulation can be detected by various medical symptoms. Because the signs are not discernable by the naked eye, however, humans are said to have a hidden ovulation. Ovulating women experience a gradual three-day rise in body temperature, on average 0.4 to 0.6 degrees Fahrenheit (0.2 degress Celsius). The temperature elevation persists until the day of menses which marks the end of the menstrual cycle. Furthermore, some women may experience novel discomfort or pain in their lower abdomen during ovulation termed Mittelschmerz ("midpain") that is most likely caused by irritation of the abdominal wall from the blood and fluid escaping from the ruptured follicle. Lastly, the chemical composition of a woman's cervical mucus will shift during ovulation, changing in composition to better accommodate sperm. The mucus is said to be clear, stretchable, and sticky, resembling raw egg white. Beyond these physiological signs, a study suggests that women's preferences in men shift during ovulation, appealing toward a more primitive drive to find a suitable mate. Another study has concluded that women subtly improve their facial attractiveness during ovulation. The significance and accuracy of these studies have been hotly debated among the medical and scientific professions.

New research: follicular waves

Emerging research spearheaded by Baerwald et al. suggests that the menstrual cycle may not regulate follicular growth as strictly as previously thought. In particular, the majority of women during a typical twenty-eight day cycle experience two or three "waves" of follicular development, with only the final wave being ovulatory. The remainder of the waves are anovulatory, characterized by the developed preovulatory follicle falling into atresia (a major anovulatory cycle) or no preovulatory follicle being chosen at all (a minor anovulatory cycle). The phenomenon is similar to the follicular waves seen in cows and horses. In these animals, a large cohort of early tertiary follicles develop consistently during the follicular phase of the menstrual cycle, suggesting that the endocrine system does not regulate folliculogenesis stringently. This revelation challenges our current understanding of follicular development and menstrual cycle dynamics and may also explain why traditional methods of natural family planning and birth control using the idealized cycle are so ineffective. Specifically, this discovery is a likely explanation for pregnancies caused by sexual intercourse when a woman is sure she should not be ovulating. Another explanation is, of course, that the woman has mistakenly assumed that she ovulates on day 14, when in fact, she ovulates earlier or later in her cycle.

Induced ovulation and contraception

The majority of oral contraceptives and conception boosters focus on the ovulatory phase of the menstrual cycle because it is the most important determinant of fertility. Hormone therapy can positively or negatively interfere with ovulation and can give a sense of cycle control to the woman. Follicle stimulating hormone, gonadotropin releasing hormone (GnRH), and estradiol have been purified in the laboratory. Chemical analogues of estradiol and progesterone have also been synthesized. Recall that GnRH is an upstream inducer of both FSH and LH secretion. Generally, administered FSH or GnRH can induce ovulation by rapidly accelerating the pace of folliculogenesis, allowing for conception. Estradiol and progesterone, taken in the form of oral contraceptives, mimics the hormonal levels of the menstrual cycle and engage in negative feedback of folliculogenesis and ovulation.

Ovulation in animals

Some interesting aspects can be noted here:
- Ovulation in camels is induced by male pheromones. In caravans without bulls female camels don't have an estrus.
- In cats ovulation is induced mechanically by the male through copulation.
- Chickens have an ovulation almost every day.
- The embryos of some Marsupial species enter embryonic diapause (or delayed implantation) after fertilization.

References

- Baewald AR, Adams GP, Pierson RA. 2004. A new model for ovarian follicular development during the human menstrual cycle. Fertil Steril 80:116-122 ([http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Abstract&list_uids=12849812 Abstract])
- Chabbert Buffet N, Djakoure C, Maitre SC, Bouchard P. 1998. Regulation of the human menstrual cycle. Front Neuroendocrinol 19:151-86. ([http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9665835/ Abstract])
- Fortune JE. 1994.Ovarian follicular growth and development in mammals. Biol Reprod: 50:225-232
- Guraya SS, Dhanju CK. 1992. Mechanism of ovulation -- an overview. Indian J Exp Biol 30:958-967
- Roberts SC, Havlicek J, Flegr J, Hruskova M, Little AC, Jones BC, Perrett DI, Petrie M. 2003. Female facial attractiveness increases during the fertile phase of the menstrual cycle. Proc Biol Sci: 271 Suppl 5 ([http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15503991&query_hl=3 Abstract]) Category:Reproductive system Category:Developmental biology ja:排卵

Embryo

: For musical bands with the name "Embryo" see Embryo (band) Embryo (band) An embryo (Greek: έμβρυον) is a diploid eukaryote in its earliest stage of development. In organisms that reproduce sexually, once a sperm fertilizes an egg cell, the result is a cell called the zygote that has all the DNA of two parents. In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism. The term embryo refers to the early stages of this development, after the zygote has divided at least once, but before the process has completed to produce a new individual.
- Plants: In botany, a plant embryo is part of a seed, consisting of precursor tissues for the leaves, stem (see hypocotyl), and root (see radicle), as well as one or more cotyledons. Once the embryo begins to germinate — grow out from the seed — it is called a seedling.
- Animals: The embryo of vertebrates is defined as the organism between the first division of the zygote (a fertilized ovum) until it becomes a fetus. An embryo is called a fetus at a more advanced stage of development and up until birth or hatching. In humans, this is from the eighth week of gestation.
- Stages: morula-> blastula->gastrula.

External link

- [http://www.genefaith.org/ethgen/pages/databases/resources/humdevchart.html Chart of human development] Category:Developmental biology ja:胚 simple:Embryo

Implantation

Pregnancy#Implantation

Estrous 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

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

Myometrium

The myometrium is the middle layer of the uterine wall consisting of smooth muscle cells and supporting stromal and vascular tissue. The inner layer of the uterine wall is the endometrium or uterine lining, and the outer layer the serosa or peritoneum. The myometrium stretches (the smooth muscle cells expand in size, rather than number) during pregnancy to allow for the harboring of the pregnancy, and contracts in a coordinated fashion during the process of labor. After delivery the myometrium contracts to expel the placenta and reduce blood loss. Lack of contraction at this stage is termed uterine atony. After pregnancy the uterus returns to its nonpregnant size by a process of myometrial involution. Neoplasms of the myometrium are very common, termed uterine leiomyomata or fibroids. Their malignant version, leiomyosarcoma, is rare. Category: pelvis

Histology

and eosin. This individual suffers from emphysema.]] Histology is the study of tissue sectioned as a thin slice, using a microscope. It can be described as microscopic anatomy. Histology is an essential tool of biology. Histopathology, the microscopic study of diseased tissue, is an important tool of anatomical pathology since accurate diagnosis of tumors and other diseases usually requires histopathological examination of samples. The trained technicians who perform the work of processing, thin sectioning, and staining these tissues are Histologic Technicians (HT) and Histologic Technologists (HTL). Their field of study is called histotechnology. Histological examination of tissues starts with surgery, biopsy or autopsy. The tissues are then fixed in a fixative, a process that stabilizes the tissues to prevent decay. The most common fixative is formalin (10% formaldehyde in water). The samples are then immersed in multiple baths of progressively more concentrated ethanol, to dehydrate the tissue, followed by a clearing agent such as chloroform, xylene or Histoclear, and finally hot molten paraffin wax (impregnation). During this 12 to 16 hour process, paraffin wax will replace the water: soft, moist tissues are turned into a hard paraffin block, which is then placed in a mould containing more molten wax (embedded) and allowed to cool and harden. This allows the sectioning of tissues into very thin (5 - 7 micrometer) sections using a microtome. These slices, thinner than the average cell, are then placed on a glass slide for staining. A 5 to 7 micrometer slice of most tissues is almost completely transparent with very little visible detail. To see the tissue under a microscope, the sections are stained with one or more pigments. Hematoxylin and eosin are among the most commonly used stains in histology and histopathology. Hematoxylin colors nuclei blue, eosin colors the cytoplasm pink. Other compound used to color tissue sections include saffron, silver salts and numerous natural and artificial dyes originally developed to stain cloth fibers. The science of tissue staining is called histochemistry. Recently, antibodies are used to stain specific proteins: this is called immunohistochemistry. This technique has greatly increased the ability to identify categories of cells under a microscope. Other advanced techniques include in situ hybridization to identify specific DNA or RNA molecules, and confocal microscopy. Digital cameras are increasingly used to capture histological and histopathological images. In the 19th Century, histology was an academic discipline in its own right. The 1906 Nobel Prize in Physiology or Medicine was awarded to two histologists, Camillo Golgi and Santiago Ramón y Cajal. They had dueling interpretations of the neural structure of the brain based in differing interpretations of the same images.

Histological classification of animal tissues

- epithelium: the lining of glands, bowel, skin and some organs like the liver, lung, kidney,
- endothelium: the lining of blood and lymphatic vessels,
- mesothelium: the lining of pleural, peritoneal and pericardial spaces,
- mesenchyme: the cells filling the spaces between the organs, including fat, muscle, bone, cartilage and tendon cells,
- blood cells: the red and white blood cells, including those found in lymph nodes and spleen,
- neurons: cells forming the brain, nerves and some glands like the pituitary and adrenal glands,
- germ cells: reproductive cells, spermatozoa in men, oocytes in women,
- placenta: a specialized organ essential for the growth of the fetus in the mother's uterus, and
- stem cells: cells able to turn into one or several of the above types. Note that tissues from plant, fungus and microorganisms can also be examined histologically. Their structure is very different from animal tissue.

Related sciences

- Cytology, the study of loose cells, for example cells taken from the cervix during a cervicovaginal smear (pap smear). The cells are directly spread on a glass slide and stained.
- Cell biology the study of structures smaller than cells, within the cell itself, called organelles. It usually requires an electron microscope and biochemistry techniques.
- Anatomy, is the study of organs visible by the naked eye; and
- Morphology, which studies entire organisms.

Histological artifacts

A histological artifact is a structure or feature that is absent in living tissues, but introduced during preparation or staining. Troubleshooting and minimizing artifacts is a major part of the discipline of histochemistry.

References

1. Merck Source (2002). [http://www.mercksource.com/pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszSzcommonzSzdorlandszSzdorlandzSzdmd_a-b_00zPzhtm Dorland's Medical Dictionary]. Retrieved 2005-01-26. 2. Stedman's Medical Dictionaries (2005). [http://stedmans.com/ Stedman's Online Medical Dictionary]. Retrieved 2005-01-26.

External links

- [http://www.ihcworld.com/protocol_database.htm Histology Protocols]
- [http://www.immunoportal.com Immunohistochemistry - In Situ Hybridization]
- [http://www.kumc.edu/instruction/medicine/anatomy/histoweb Histoweb]
- [http://www.visualhistology.com/onlinecommunity/index.php VisualHistology.com Online Community] Category:Anatomy Category:Histology Category:Histopathology ja:組織学 ms:Histologi

Leukocyte

White blood cells (also called leukocytes or immune cells) are a component of blood. They help to defend the body against infectious disease and foreign materials as part of the immune system. There are normally between 4x10⁹ and 11x10⁹ white blood cells in a litre of healthy adult blood - about 7 000 to 25 000 white blood cells per drop. In conditions such as leukemia this may rise to as many as 50 000 white blood cells in a single drop of blood. As well as in the blood, white cells are also found in large numbers in the lymphatic system, the spleen, and in other body tissues.

Nomenclature

The name "white cells" derives the from the fact that after centrifugation of a blood sample, the white cells are found in the Buffy coat, a small fraction between the hematocrit and the blood plasma, which is white in color (or sometimes green, if there are large amounts of neutrophils in the sample, which are high in green myeloperoxidase). Any of various blood cells that have a nucleus and cytoplasm, separate into a thin white layer when whole blood is centrifuged, and help protect the body from infection and disease. White blood cells include neutrophils, eosinophils, basophils, lymphocytes, and monocytes. Also called leukocyte, white cell, white corpuscle.

Types

There are three major types of white blood cells.

Granulocytes

Granulocytes are a category of white blood cells, characterised by the fact that all types have differently staining granules in their cytoplasm on light microscopy. There are three types of granulocytes: neutrophils, basophils, and eosinophils (named according to their staining properties).

Lymphocytes

Lymphocytes are much more common in the lymphatic system, and include the so-called "killer T-cells". The blood has three types of lymphocytes: B cells, T cells and natural killer cells. B cells make antibodies that bind to pathogens to enable their destruction. CD4+ (helper) T cells co-ordinate the immune response (they are what becomes defective in an HIV infection). CD8+ (cytotoxic) T cells and natural killer cells are able to kill cells of the body that are infected by a virus.

Monocytes

Monocytes share the 'vacuum cleaner' function of neutrophils, but are much longer lived as they have an additional role. They present pieces of pathogens to T cells so that the pathogens may be recognised again and killed, or so that an antibody response may be mounted. Monocytes are also known as macrophages after they leave the bloodstream and enter tissue.

Diseases

- Leukopenia is a disease symptom defined as a lower than normal number of white blood cells in the blood.
- Leukocytosis refers to an increase in the number of white blood cells in the blood.
- Leukemia and lymphoma are two types of cancer in which white blood cells multiply out of control.

Other tissue cells

- Histiocytes, found in the lymphatic system and other body tissues, but not normally in blood:
- Macrophages
- Dendritic cells
- Mast cells

External links

Category:Blood cells ko:백혈구 ja:白血球 simple:White blood cell

Hormones

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 incl