Female sexual cycle
The menstrual cycle or ovarian cycle consists of a series of regular changes that naturally occur in the female reproductive system (especially in the uterus and ovaries) which make pregnancy or menstruation possible, in case the first does not take place, during this cycle the oocytes develop.
About 80% of women report symptoms from one to two weeks before menstruation.
First menstruation
The first menstruation occurs between the ages of eleven and fifteen and is called menarche. The average age of menarche is generally higher in developed countries than in developing countries. It appears when all the parts of the girl's reproductive system have matured and work together. This indicates the beginning of reproductive capacity. It constitutes the main psychological marker of the transition from childhood to adulthood.
After menopause, menstruation stops occurring due to the loss of hormonal stimulation, ranging between 45 and 55 years of age. The blood loss normally lasts around 2 to 7 days.
Phases of the menstrual cycle
Menstruation
Also called rule, period or menstrual bleeding, it starts on the first day of the menstrual cycle. During this phase, the endometrium is shed along with a quantity of blood. This bleeding is usually taken as a sign that a woman is not pregnant (although there are some exceptions that can cause bleeding during pregnancy, some specifically in early pregnancy, which can also cause heavy bleeding).
The average menstruation usually lasts a few days, usually between three and five, although those between two and seven days are considered normal. Blood loss is usually about 35 ml, with between 10 and 80 ml being considered normal.. Women who have menorrhagia are predisposed to anemia. An enzyme called plasmin prevents menstrual fluid from clotting.
During the first days of menstruation, pain in the abdomen, back, or upper thighs is common. Severe uterine pain is known as dysmenorrhea and is more common among adolescent girls and young women (affecting 67.2% of adolescent girls). Dysmenorrhea can be explained as an inflammatory process. Although many aspects are still unknown, it is known that the process is mediated by prostaglandins and polymorphonuclear cells. Progesterone has anti-inflammatory properties, as progesterone levels fall, the inflammatory process is triggered. When menstruation begins, the symptoms of premenstrual syndrome, such as irritability or swelling and pain in the breasts, decrease. There are a wide variety for sale. of sanitary products for women to use during menstruation (pads, tampons and cups).
Preovulation
Also called the follicular phase or proliferative phase since during this period the endometrium grows and thickens due to the action of estradiol. It usually lasts from the first to the thirteenth day of the cycle.
Through the influence of follicle-stimulating hormone (FSH), which increases during the first days of the cycle, a few ovarian follicles are stimulated. These follicles, present from birth, develop in a process called folliculogenesis.
Folliculogenesis involves the formation and maturation of the ovarian follicle, a densely packed shell of somatic cells that contains an immature oocyte and where meiosis occurs. This describes the progression from a series of small primordial follicles into large preovulatory follicles that occurs in part during the menstrual cycle. It lasts 2 months from start to finish.
Subsequently, all follicles stop growing and enter into atresia; except one. This is the dominant follicle and will continue until maturity, forming the Graafian follicle, which contains the oocyte that is released at ovulation.
The biological mechanisms by which the dominant follicle is selected are still not clear. Randomly, at the beginning of recruitment, some follicles will progress and start the process faster than others, which will give them a certain advantage. Within this group, there will be some that have a greater number of receptors for FSH than others, and also, within these, some of these follicles will have more efficient receptors than others. With which, a process of positive selection will take place for the follicle that starts faster, has more receptors and is of better quality, which will make it hoard more FSH, causing the other follicles to slow down their growth and finally become dazed.
As the follicles mature, they secrete increasing amounts of estradiol, an estrogen. Estradiol levels increase significantly when the dominant follicle is selected, as it secretes a huge amount. Estrogens initiate the formation of a new layer of the endometrium in the uterus (proliferative endometrium). Estrogen also stimulates the crypts in the cervix to produce fertile cervical mucus, which will be identified by women who check their most fertile days.
Ovulation
In a 28-day cycle, it occurs between the fourteenth and fifteenth day of the cycle. The oocyte is released from the ovary and is conducted to the uterus through the fallopian tube (Uterine Tube).
During the follicular phase, estradiol suppresses the production of luteinizing hormone (LH) from the anterior pituitary gland. When the ovum is about to reach maturity, estradiol levels reach a threshold where this effect is reversed and estrogen stimulates the production of a large amount of luteinizing hormone. This process, known as the luteinizing hormone spike, begins around day 12 of an average cycle and can last for 48 hours.
How the exact mechanism of these opposing luteinizing hormone responses to estradiol works is not yet understood.:86 In animals, a GnRH surge precedes the luteinizing hormone surge, thereby which suggests that the greatest effect of estrogen is in the hypothalamus, which in turn controls the secretion of GnRH.:86 This is due to the presence of two types of estrogen receptors in the hypothalamus: estrogen receptor alpha, responsible for the negative response in the estradiol-LH cycle, and estrogen receptor beta, responsible for the positive relationship between estradiol and LH. However, in humans, high levels of estradiol can cause LH surges, even when GnRH levels and pulse rate are constant,:86 suggesting that estrogen acts directly on the pituitary to trigger the LH surge.
This LH surge is what causes ovulation, as it causes the activation of pro-inflammatory genes that weaken and rupture the follicular wall, causing the follicle to release its secondary oocyte.
Which of the two ovaries will ovulate which time, the right or the left, appears to be random, and it is not known whether there is coordination between the two sides. Sometimes both ovaries release an egg, if both are fertilized, result in twin brothers (dizygotic twins, also called twins).
After being released from the ovary into the peritoneal space, the oocyte is captured by the fallopian tubes through the fimbria or ovarian fringe, which is a tissue located at the end of each fallopian tube. After about a day, an unfertilized oocyte disintegrates and is expelled by vaginal bleeding during the next menstruation, thus beginning a new cycle. On the other hand, if fertilization occurs, the oocyte completes its maturation, giving rise to the ovum. ripe.
Fertilization by a sperm usually occurs in the ampulla, the widest section of the fallopian tubes. A fertilized egg immediately begins the process of embryogenesis or development. This developing embryo takes about three days to reach the uterus and another three to take root in the endometrium. By then it usually has reached the blastocyst stage.
In some women, ovulation causes characteristic pains called mittelschmerz (German for middle pain). The sudden hormonal shift during ovulation can also sometimes cause midlife bleeding. cycle.
Postovulation
Also known as the luteal phase or secretory phase. It usually lasts from the 16th to the 28th day of the cycle.
The corpus luteum, which comes from the Graafian follicle after the oocyte is released, plays an important role in this phase. This body continues to grow for some time after ovulation and produces significant amounts of hormones, particularly progesterone. Progesterone plays a vital role in making the endometrium receptive for implantation of the blastocyst and in supporting it during early pregnancy; as a side effect it raises the woman's basal temperature. In addition, it produces a myorelaxation of the smooth muscles to facilitate the implantation of the embryo; This relaxation results in a decrease in tension, sleep, and slight constipation. Another important effect of progesterone is an increase in breast tension due to increased gland size and growth.
On the other hand, it stops the production of FSH and LH that it needs to maintain itself, so progesterone levels decrease and the corpus luteum atrophies. Falling progesterone levels trigger menstruation and the start of the next cycle. From ovulation to the drop in progesterone that causes menstruation, two weeks usually pass. The follicular phase tends to vary in each woman from cycle to cycle, contrasting with the luteal phase, which remains the same.
If the egg is fertilized, progesterone levels are maintained and therefore the corpus luteum is not lost. In addition, the resulting embryo produces human chorionic gonadotropin (hCG), very similar to luteinizing hormone, allowing the corpus luteum to be preserved. Since this hormone is only produced by the embryo, most pregnancy tests look for the presence of this hormone.
Cycle duration
Although many people believe that the average menstrual cycle lasts about 28 days, a large-scale study of more than 30,000 cycles from more than 2,300 women revealed that the average cycle lasts 29.1 with a standard deviation of seven days and mean and a prediction interval between 15 and 45 days. In this study, the subset of data with cycle lengths between 15 and 45 days had a mean of 28.1 days with a standard deviation of four days. A smaller study of 140 women conducted in 2006 found a median of 28.9 days.
Variability in the length of the menstrual cycle is greatest in women under twenty-five years of age and least in women between 35 and 39 years of age. Variability increases again in women between 40 and 44 years of age. Normally, variations of cycle length between eight and twenty days is considered moderate irregularity, and a variation of 21 days or more is considered highly irregular.
It has long been believed that the length of the cycle is associated with the moon. In 1979 a study of 305 women revealed that approximately one third of the subjects had lunar menstrual cycles, ie a mean cycle length of 29.5 days plus or minus one day. At least two-thirds of the subjects began their cycles in the bright half of the lunar cycle, although a random distribution was expected. Another study revealed that a significant number of menses began on a new moon.
Fertile Period
The most fertile period (the time most likely to conceive as a result of sexual intercourse) occurs sometime between five days before and one to two days after ovulation. In a 28-day cycle with a luteal phase of 14, this moment corresponds to the second week, and the beginning of the third. A wide variety of methods have been developed to help women know when in their cycle they are most fertile or infertile. These systems are known as fertility awareness methods.
The method that measures fertility index based solely on cycle length is called the Ogino-Knaus method. Methods that require observation of one or more of the three signs of fertility (basal body temperature, cervical mucus, and position cervical) are known as symptom-based methods. The kits available for urine analysis detect the increase in luteinizing hormone that occurs between 24 to 36 hours before ovulation, they are called ovulation predictor kits. There are also kits called fertility monitors, which are computerized devices that interpret basal body temperature, urinalysis results, or changes in saliva.
A woman's fertility is also affected by her age. As a woman's total reserve of eggs is formed in her fetal stage to be ovulated decades later, it has been suggested that this long lifespan may cause Egg chromatin is more vulnerable to division, breakage and mutation problems than sperm chromatin, which is produced continuously throughout a man's reproductive life. However, despite this hypothesis, similar aging has been observed in both cases.
Last menstruation
The last menstruation is known as menopause, the stage in which a woman stops menstruating. The average age at which menopause occurs is 51.4 years. However, the age of menopause varies from woman to woman, and is generally between 40 and 55. This last bleeding is preceded by the climacteric, which is the transition phase between the reproductive and non-reproductive stage of the woman. However, since the last consensus of the WHO (World Health Organization) it is recommended to abandon the term climacteric to avoid confusion and it is replaced by the term perimenopause.
Disorders in the menstrual cycle
Irregular ovulation is called oligoovulation. Absence of ovulation is called anovulation. You can have your period without ovulation preceding it: an anovulatory cycle. In some cycles, follicular development may begin but not complete, however, estrogens will form and stimulate the uterine lining. Anovulatory flow arises from a very thick endometrium, caused by having continuously high levels of estrogen. This flow is called estrogen breakthrough bleeding. Anovulatory bleeding triggered by a sharp drop in estrogen levels is called swings. Anovulatory cycles often occur before menopause (perimenopause) and in women with polycystic ovary syndrome.
Excessively little flow (less than 10 mL) is called hypomenorrhea. Cycles of less than 21 days or less are proiomenorrhea. Frequent but irregular menstruation is known as metrorrhagia. Sudden heavy bleeding in amounts greater than 80 ml is called menorrhagia. Heavy menstruation that occurs frequently and irregularly is menometrorrhagia. The term for cycles that exceed 35 days is opsomenorrhea. Amenorrhea is the absence of menstruation for three to six months (without being pregnant) during the reproductive years.
George Preti, an organic chemist at the Monell Chemical Senses Center in Philadelphia, and Winnefred Cutler, of the department of psychology at the University of Pennsylvania, found that women with irregular menstrual cycles, when exposed to male sweat extract, became regular. One possible explanation could be that the axillae contain pheromones, as in other mammals.
Ovulation suppression
Hormonal contraception
While some birth control methods don't affect the menstrual cycle, hormonal ones work by interrupting it. Progesterone negative feedback decreases the pulse rate of gonadotropin-releasing hormone (GnRH) released by the hypothalamus and decreases the pulse rate of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) produced by the pituitary gland. Low FSH levels inhibit follicular development, preventing an increase in estradiol levels. The negative feedback of progesterone and the lack of positive feedback of estrogen during LH release prevent the mid-cycle LH surge. The inhibition of follicular development and the absence of LH prevent ovulation.
The degree of ovulation suppression in progestin-only contraceptives depends on the activity of the progestin and the dose. Low doses of progestogen contraceptives, the classic pills, Norplant and Jadelle subdermal implants, and the Mirena intrauterine system, inhibit ovulation in 50% of cycles, and their contraceptive effectiveness rests mainly on other effects, such as thickening of cervical mucus. Mid-dose progestogen-only contraceptives, the Cerazette pill and Nexplanon subdermal implant, allow some follicular development, but inhibit ovulation in 97-99% of cycles. The same changes in cervical mucus occur as with low doses of progestin. High-dose drugs, such as Depo Provera and Noristerat injectables, totally inhibit follicular development and ovulation.
Combined hormonal contraceptives contain estrogen and progestin. Negative feedback of estrogen in the pituitary gland causes FSH emission to decrease, making this type of contraceptive more effective in inhibiting follicular development and ovulation. Estrogen also reduces the incidence of breakthrough bleeding. Several combined hormonal contraceptives, the pill, NuvaRing, and the patch, are often used in a way that causes bleeding. In a normal cycle, menstruation occurs with a sudden drop in estrogen and progesterone levels. Temporary discontinuation of these contraceptives (one week of placebo or stopping use for one week) has a similar effect, making the uterine wall blood. If this bleeding is not desired, combined hormonal contraceptives should be taken continuously, although this increases the risk of bleeding.
Lactational amenorrhea
Breastfeeding causes negative feedback in the pulse of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion. Depending on the strength of this negative feedback, lactating women may experience complete suppression of follicular development, follicular development but no ovulation, or normal cycles. Ovulation suppression is more common with more frequent breastfeeding. Prolactin production in response to breastfeeding is important in maintaining lactational amenorrhea. On average, lactating women frequently experience the return of menses about fourteen and a half months after delivery. There is a wide range of individual response, with some experiencing the return of menstruation within two months and others remaining amenorrheic for up to 42 months.
Effects on other systems
Some women with neurological diseases have experienced increased disease activity during their menstrual cycle. For example, falling estrogen levels can trigger migraines, especially when the woman suffering from them is taking the birth control pill. Many women with epilepsy have more seizures in a pattern related to the menstrual cycle. This is called catamenial epilepsy. There appear to be different patterns (seizures may coincide with menstruation or ovulation) and the frequency of seizures is not always the same. Using a particular definition, a group of scientists discovered that one third of women with intractable partial epilepsy have catamenial epilepsy. The decrease in progesterone and the increase in estrogen could cause seizures. Recent studies have shown that high doses of estrogen can cause or worsen seizures, while high doses of progesterone can serve as an antiepileptic drug. According to studies in medical journals, menstruating women are 1.68 times more likely to commit suicide. Mice have been used in an experimental system to investigate the possible mechanisms by which the levels of the sex steroid hormone can regulate the functions of the nervous system. During part of the heat, when progesterone is high, the level of GABA A subtype delta receptor neurons was high. Since these receptors are inhibitory, neurons with more delta receptors are less likely to be used than those with fewer. During the part of heat where estrogen was higher than progesterone, the number of delta receptors decreased, increasing the level of neural activity, in turn increasing anxiety and susceptibility to seizures.
Estrogen levels can affect thyroid behavior. For example, during the luteal phase (when estrogen levels are low), the velocity of blood in the thyroid is slower than during the follicular phase (during which estrogen levels are higher).
Among women who live together, the onset of menstruation tends to be synchronized. This effect was first described in 1971 and a possible explanation was found in 1998, by the effect of pheromones. Subsequent research has led to rethinking this hypothesis.
Biological and etymological associations
The word n#34;menstruation n#34; is etymologically related to the moon, derived from the Latin mensis, month, which in turn comes from the Greek mene, moon.
Some authors believe that historically, women in traditional societies without night lighting ovulated on the full moon and menstruated on the new moon, and one author documents controversial attempts to use this association to improve the calendar method of regulating the conception.
A few studies in humans and other animals have found that artificial light at night influences the menstrual cycle in humans and estrous in mice (cycles are more regular in the absence of artificial light at night). In turn, it has been suggested that bright light in the morning helps regulate the cycle. One author has suggested that the sensitivity of female cycles to night light is caused by nutritional deficiencies of certain vitamins and minerals.
Some studies show a correlation between the human menstrual cycle and the lunar cycle, while a meta-analysis of studies since 1996 shows no correlation. of the nights outside their houses, talking and sleeping, so they were the ideal population to detect the lunar influence, which, despite everything, was not found.
The influence of the menstrual cycle on smoking withdrawal syndrome
In Spain, according to data from the National Institute of Statistics (INE), the number of smokers has increased by 3.3% between 2017 and 2019, reaching 23.3% of the population. By sex and for the year 2020, this represents a percentage of smokers of 23.3% in men and 16.4% in women.
There are numerous techniques for quitting smoking, including group therapy, patches, gum, and meditation. But, in addition, in the case of women, trying to quit smoking during certain days of the month can make it easier to achieve it, according to data obtained in a study from the University of Pennsylvania and the University of Montreal.
These studies focused on: verifying whether there are differences in the neural circuits linked to compulsive smoking according to sex and determining whether the changes in cortical activity associated with nicotine withdrawal fluctuate in line with the hormonal variations produced during the menstrual cycle.
The results obtained in these studies carried out with MRI and, taking into account the day of the female cycle, show that, although there are no significant differences between men and women in relation to the neural circuits involved in the excessive desire to smoke, did observe that neural firing patterns in women varied considerably throughout their menstrual cycle. Specifically, certain areas of their frontal, temporal, and parietal cortices showed greater activation during the follicular phase, while during the luteal phase it registered reduced activity in the hippocampus.
Adrianna Mendrek, lead author of the Université de Montréal study explains: "Our results reveal that uncontrolled urges to smoke are strongest at the beginning of the follicular phase. Hormonal decreases in estrogen and progesterone possibly accentuate the withdrawal syndrome and increase the activity of neural circuits associated with the desire to smoke. According to the scientist, it could be easier for women to overcome the symptoms related to smoking withdrawal during the mid-luteal phase, that is, after ovulation, when estrogen and progesterone levels rise.
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