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100-416: Generally, the duct fully obliterates (narrows and disappears) during the 5–6th week of fertilization age (9th week of gestational age ), but a failure of the duct to close is termed a vitelline fistula. This results in discharge of meconium from the navel (umbilicus). About two percent of fetuses exhibit a type of vitelline fistula characterized by persistence of the proximal part of the vitelline duct as

200-414: A diverticulum protruding from the small intestine , Meckel's diverticulum , which is typically situated within two feet of the ileocecal junction and may be attached by a fibrous cord to the abdominal wall at the umbilicus. The yolk sac can be seen in the afterbirth as a small, somewhat oval-shaped body, the diameter of which varies from 1 mm to 5 mm. It is situated between the amnion and

300-411: A genital ulcer ; even if they do not, they increase the risk of both acquiring and passing on HIV up to ten-fold. Hepatitis B can also be transmitted through sexual contact. Globally, there are about 257 million chronic carriers of hepatitis B. HIV is one of the world's leading infectious killers; in 2010, approximately 30 million people were estimated to have died because of it since the beginning of

400-454: A sperm-specific protein Izumo on the head binds to Juno receptors on the oocyte membrane. Once it is bound, two blocks to polyspermy then occur. After approximately 40 minutes, the other Juno receptors on the oocyte are lost from the membrane, causing it to no longer be fusogenic. Additionally, the cortical reaction will happen which is caused by ovastacin binding and cleaving ZP2 receptors on

500-460: A stroke can also largely impact on the ability to engage in sexual intercourse. Although disability-related pain, including as a result of cancer , and mobility impairment can hamper sexual intercourse, in many cases, the most significant impediments to sexual intercourse for individuals with a disability are psychological. In particular, people who have a disability can find sexual intercourse daunting due to issues involving their self-concept as

600-426: A boy who is 1 to 3 years older than they are. Between 1988 and 2002, the percentage of people in the U.S. who had sexual intercourse between the ages of 15 and 19 fell from 60 to 46 percent for never-married males, and from 51 to 46 percent for never-married females. In humans, sexual intercourse and sexual activity in general have been reported as having health benefits as varied as increased immunity by increasing

700-414: A day of ovulation , which, in turn, occurs on average 14.6 days after the beginning of the preceding menstruation (LMP). There is also considerable variability in this interval, with a 95% prediction interval of the ovulation of 9 to 20 days after menstruation even for an average woman who has a mean LMP-to-ovulation time of 14.6. In a reference group representing all women, the 95% prediction interval of

800-504: A form of safe sex and contraception. Condoms are widely recommended for the prevention of sexually transmitted infections (STIs). According to reports by the National Institutes of Health (NIH) and World Health Organization (WHO), correct and consistent use of latex condoms reduces the risk of HIV/AIDS transmission by approximately 85–99% relative to risk when unprotected. Condoms are rarely used for oral sex and there

900-604: A lack of "dialogue around this population's human right to consensual sexual expression, undertreatment of menstrual disorders, and legal and systemic barriers". Women with intellectual disability may lack sexual health care and sex education. They may not recognize sexual abuse. Consensual sexual intercourse is not always an option for some. Those with intellectual disability may have limited knowledge and access to contraception, screening for sexually transmitted infections and cervical cancer. Sexual intercourse may be for reproductive, relational, or recreational purposes. It often plays

1000-517: A man's penis into another person's rectum, but may also mean the use of sex toys or fingers to penetrate the anus, or oral sex on the anus ( anilingus ), or pegging . Oral sex consists of all the sexual activities that involve the use of the mouth and throat to stimulate genitalia or anus. It is sometimes performed to the exclusion of all other forms of sexual activity, and may include the ingestion or absorption of semen (during fellatio ) or vaginal fluids (during cunnilingus ). Fingering involves

1100-470: A member of the same cohort. It may be regarded as a mechanism of kin selection . Recent studies have shown that the egg is not passive during this process. In other words, they too appear to undergo changes that help facilitate such interaction. After the sperm enters the cytoplasm of the oocyte, the tail and the outer coating of the sperm disintegrate. The fusion of sperm and oocyte membranes causes cortical reaction to occur. Cortical granules inside

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1200-480: A mode called by him as epigenetic . In 1651 William Harvey refuted Aristotle's idea that menstrual blood could be involved in the formation of a fetus , asserting that eggs from the female were somehow caused to become a fetus as a result of sexual intercourse . Sperm cells were discovered in 1677 by Antonie van Leeuwenhoek , who believed that Aristotle had been proven correct. Some observers believed they could see an entirely pre-formed little human body in

1300-497: A neurotransmitter. This behavior is characterized by a fixation on sexual intercourse and disinhibition. It was proposed that this 'addictive behavior' be classified in DSM-5 as an impulsive–compulsive behavioral disorder. Addiction to sexual intercourse is thought to be genetically linked. Those having an addiction to sexual intercourse have a higher response to visual sexual cues in the brain. Those seeking treatment will typically see

1400-505: A physician for pharmacological management and therapy. One form of hypersexuality is Kleine–Levin syndrome . It is manifested by hypersomnia and hypersexuality and remains relatively rare. Sexual activity can directly cause death , particularly due to coronary circulation complications, which is sometimes called coital death, coital sudden death or coital coronary. However, coital deaths are significantly rare. People, especially those who get little or no physical exercise, have

1500-605: A primary form of sexual activity. Researchers commonly use sexual intercourse to denote penile–vaginal intercourse while using specific words, such as anal sex or oral sex , for other sexual behaviors. Scholars Richard M. Lerner and Laurence Steinberg state that researchers also "rarely disclose" how they conceptualize sex "or even whether they resolved potential discrepancies" in conceptualizations of sex. Lerner and Steinberg attribute researchers' focus on penile–vaginal sex to "the larger culture's preoccupation with this form of sexual activity", and have expressed concern that

1600-462: A receptive partner during anal intercourse. The study said that fewer women reported engaging in anal sex than other partnered sexual behaviors. It was estimated that 10% to 14% of women aged 18 to 39 years old practiced anal sex in the past 90 days, and that most of the women who engage in anal sex said they practiced it once a month or a few times a year. The prevalence of sexual intercourse has been compared cross-culturally. In 2003, Michael Bozon of

1700-461: A role in personal decisions about sexual intercourse or other sexual activity, such as decisions about virginity , or legal and public policy matters. Religious views on sexuality vary significantly between different religions and sects of the same religion, though there are common themes, such as prohibition of adultery. Reproductive sexual intercourse between non-human animals is more often called copulation , and sperm may be introduced into

1800-416: A sexual being, or a partner's discomfort or perceived discomfort. Temporary difficulties can arise with alcohol and sex , as alcohol can initially increase interest through disinhibition but decrease capacity with greater intake; however, disinhibition can vary depending on the culture. People with mental disabilities also are subject to challenges in participating in sexual intercourse. This can include

1900-468: A slightly increased risk of triggering a heart attack or sudden cardiac death when they engage in sexual intercourse or any vigorous physical exercise that is engaged in on a sporadic basis. Regular exercise reduces, but does not eliminate, the increased risk. Sexual intercourse, when involving a male participant, often ends when the male has ejaculated, and thus the partner might not have time to reach orgasm . In addition, premature ejaculation (PE)

2000-429: A strong role in human bonding . In many societies, it is normal for couples to have sexual intercourse while using some method of birth control, sharing pleasure and strengthening their emotional bond through sexual activity even though they are deliberately avoiding pregnancy. In humans and bonobos , the female undergoes relatively concealed ovulation so that male and female partners commonly do not know whether she

2100-522: A surgery. Obstacles that those with disabilities face with regard to engaging in sexual intercourse include pain, depression , fatigue, negative body image , stiffness, functional impairment, anxiety, reduced libido , hormonal imbalance, and drug treatment or side effects. Sexual functioning has been regularly identified as a neglected area of the quality of life in patients with rheumatoid arthritis . For those that must take opioids for pain control, sexual intercourse can become more difficult. Having

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2200-416: A variety of safe sex methods that are practiced by heterosexual and same-sex couples, including non-penetrative sex acts, and heterosexual couples may use oral or anal sex (or both) as a means of birth control. However, pregnancy can still occur with anal sex or other forms of sexual activity if the penis is near the vagina (such as during intercrural sex or other genital-genital rubbing ) and its sperm

2300-1071: Is delayed ejaculation , which can be caused as an unwanted side effect of antidepressant medications such as fluvoxamine ; however, all SSRIs have ejaculation-delaying effects, and fluvoxamine has the least ejaculation-delaying effects. Sexual intercourse often remains possible after major medical treatment of the reproductive organs and structures. This is especially true for women. Even after extensive gynecological surgical procedures (such as hysterectomy , oophorectomy , salpingectomy , dilation and curettage , hymenotomy , Bartholin gland surgery, abscess removal, vestibulectomy , labia minora reduction, cervical conization , surgical and radiological cancer treatments and chemotherapy), sexual intercourse can continue. Reconstructive surgery remains an option for women who have experienced benign and malignant conditions. Men and women who have underwent extensive surgery should consult their medical team to understand how their treatment or surgery affects sex and how long they should wait before having sexual intercourse after

2400-424: Is ejaculated through the penis into the vagina. The sperm passes through the vaginal vault , cervix and into the uterus , and then into the fallopian tubes . Millions of sperm are ejaculated to increase the chances of fertilization (see sperm competition ), but only one is sufficient to fertilize an egg or ovum . When a fertile ovum from the female is present in the fallopian tubes, the male gamete fertilizes

2500-483: Is "the most prevalent sexual behavior among men and women of all ages and ethnicities". Clint E. Bruess et al. stated that it "is the most frequently studied behavior" and is "often the focus of sexuality education programming for youth." Weiten et al. said that it "is the most widely endorsed and practiced sexual act in our society." Regarding oral or anal intercourse, the CDC stated in 2009, "Studies indicate that oral sex

2600-444: Is a form of assisted reproductive technology , which are methods used to achieve pregnancy by artificial or partially artificial means. For artificial insemination, sperm donors may donate their sperm through a sperm bank , and the insemination is performed with the express intention of attempting to impregnate the female; to this extent, its purpose is the medical equivalent of sexual intercourse. ICI insemination, which involves

2700-509: Is also not clear if timed intercourse has an effect on a person's level of stress or their quality of life. Studies have shown no significant difference between different sex positions and pregnancy rate, as long as it results in ejaculation into the vagina. When a sperm donor has sexual intercourse with a woman who is not his partner and for the sole purpose of impregnating the woman, this may be known as natural insemination , as opposed to artificial insemination . Artificial insemination

2800-532: Is at lower ages than that of women; this group includes south European and Latin cultures (Portugal, Greece and Romania are noted) and such from Latin America (Brazil, Chile , and the Dominican Republic ). The study considered many Asian societies to also fall into this group, although matching data was only available from Thailand . In the third group, age of men and women at sexual initiation

2900-600: Is because "although an estimated 15 percent to 20 percent of men experience difficulty controlling rapid ejaculation, most do not consider it a problem requiring help, and many women have difficulty expressing their sexual needs". The American Urological Association (AUA) estimates that premature ejaculation could affect 21 percent of men in the United States. For those whose impotence is caused by medical conditions, prescription drugs such as Viagra , Cialis , and Levitra are available. However, doctors caution against

3000-411: Is common, and women often require a substantially longer duration of stimulation with a sexual partner than men do before reaching an orgasm. Scholars, such as Weiten et al., state that "many couples are locked into the idea that orgasms should be achieved only through intercourse [penile-vaginal sex]," that "the word foreplay suggests that any other form of sexual stimulation is merely preparation for

3100-502: Is commonly practiced by sexually active male-female and same-gender couples of various ages, including adolescents." Oral sex is significantly more common than anal sex. The 2010 NSSHB study reported that vaginal intercourse was practiced more than insertive anal intercourse among men, but that 13% to 15% of men aged 25 to 49 practiced insertive anal intercourse. Receptive anal intercourse was infrequent among men, with approximately 7% of men aged 14 to 94 years old having said that they were

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3200-420: Is deposited near the vagina's entrance and travels along the vagina's lubricating fluids; the risk of pregnancy can also occur without the penis being near the vagina because sperm may be transported to the vaginal opening by the vagina coming in contact with fingers or other non-genital body parts that have come in contact with semen. Safe sex is a relevant harm reduction philosophy and condoms are used as

3300-512: Is especially the case for men with a lower emotional and composite marital satisfaction. Other studies report that the lack of sexual intercourse does not significantly result in divorce, though it is commonly one of the various contributors to it. According to the 2010 National Survey of Sexual Health and Behavior (NSSHB), men whose most recent sexual encounter was with a relationship partner reported greater arousal, greater pleasure, fewer problems with erectile function, orgasm, and less pain during

3400-685: Is fertile at any given moment. One possible reason for this distinct biological feature may be formation of strong emotional bonds between sexual partners important for social interactions and, in the case of humans, long-term partnership rather than immediate sexual reproduction. Sexual dissatisfaction due to the lack of sexual intercourse is associated with increased risk of divorce and relationship dissolution, especially for men. Some research, however, indicates that general dissatisfaction with marriage for men results if their wives flirted with, erotically kissed or became romantically or sexually involved with another man ( infidelity ), and that this

3500-602: Is involuntary tensing of the pelvic floor musculature, making coitus, or any form of penetration of the vagina, distressing, painful and sometimes impossible for women. It is a conditioned reflex of the pubococcygeus muscle, and is sometimes referred to as the PC muscle. Vaginismus can be hard to overcome because if a woman expects to experience pain during sexual intercourse, this can cause a muscle spasm, which results in painful sexual intercourse. Treatment of vaginismus often includes both psychological and behavioral techniques, including

3600-422: Is known under different ancient Latin names for a variety of sexual activities, but usually denotes penile–vaginal penetration. This is often called vaginal intercourse or vaginal sex. Vaginal sex, and less often vaginal intercourse , may also denote any vaginal sexual activity, particularly if penetrative , including sexual activity between lesbian couples . Copulation , by contrast, more often denotes

3700-568: Is less risky than vaginal or anal intercourse. Many times, STIs initially do not cause symptoms, increasing the risk of unknowingly passing the infection on to a sex partner or others. There are 19 million new cases of sexually transmitted infections every year in the U.S., and, in 2005, the World Health Organization (WHO) estimated that 448 million people aged 15–49 were infected per year with curable STIs (such as syphilis , gonorrhea and chlamydia ). Some STIs can cause

3800-637: Is often based on penile–vaginal intercourse is because heterosexual couples may engage in anal or oral sex as a way of being sexually active while maintaining that they are virgins since they have not engaged in the reproductive act of coitus. Some gay men consider frot or oral sex as a way of maintaining their virginities, with penile-anal penetration used as sexual intercourse and for virginity loss, while other gay men may consider frot or oral sex as their main forms of sexual activity. Lesbians may categorize oral sex or fingering as sexual intercourse and subsequently an act of virginity loss, or tribadism as

3900-492: Is often extra-marital; the study considered the Indian subcontinent to also fall into this group, though data was only available from Nepal . In the second group, the data indicated families encouraged daughters to delay marriage, and to abstain from sexual activity before that time. However, sons are encouraged to gain experience with older women or prostitutes before marriage. Age of men at sexual initiation in these societies

4000-409: Is possible at any time of the menstrual cycle for women. Sex pheromones facilitate copulatory reflexes in various organisms, but, in humans , the detection of pheromones is impaired and they have only residual effects. Non-primate females put themselves in the crucial lordosis position and remain motionless, but these motor copulatory reflexes are no longer functional in women. During coitus,

4100-453: Is possible that individuals who engage in oral sex, but do not consider it as 'sex', may not associate the acts with the potential health risks they can bring." In other cases, condom use is a factor, with some men stating that sexual activity involving the protection of a condom is not "real sex" or "the real thing". This view is common among men in Africa, where sexual activity involving

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4200-451: Is significantly less research on behaviors with regard to condom use for anal and oral sex. The most effective way to avoid sexually transmitted infections is to abstain from sexual intercourse, especially vaginal, anal, and oral sexual intercourse. Decisions and options concerning birth control can be affected by cultural reasons, such as religion, gender roles or folklore . In the predominantly Catholic countries Ireland, Italy, and

4300-400: Is unable or poorly able to fertilize. The sperm must undergo capacitation in the female's reproductive tract, which increases its motility and hyperpolarizes its membrane, preparing it for the acrosome reaction , the enzymatic penetration of the egg's tough membrane, the zona pellucida , which surrounds the oocyte. The sperm binds through the corona radiata , a layer of follicle cells on

4400-453: Is very difficult" and that this is "because most sexually active individuals practice oral sex in addition to other forms of sex, such as vaginal or anal sex, when transmission occurs, it is difficult to determine whether it occurred as a result of oral sex or other more risky sexual activities". They added that "several co-factors may increase the risk of HIV transmission through oral sex"; this includes ulcers, bleeding gums , genital sores, and

4500-539: The chorion and may lie on the placenta or at a varying distance from it. Sometimes a narrowing of the lumen of the ileum is seen opposite the site of attachment of the duct. On this site of attachment, sometimes a pathological Meckel's diverticulum may be present. A mnemonic used to recall details of a Meckel's diverticulum is as follows: "2 inches long, within 2 feet of ileocecal valve , 2 times as common in males than females, 2% of population, 2% symptomatic, 2 types of ectopic tissue: gastric and pancreatic". In

4600-837: The mating process, especially for non-human animals; it can mean a variety of sexual activities between opposite-sex or same-sex pairings , but generally means the sexually reproductive act of transferring sperm from a male to a female or sexual procreation between a man and a woman. Although sex and having sex also most commonly denote penile–vaginal intercourse, sex can be significantly broad in its meaning and may cover any penetrative or non-penetrative sexual activity between two or more people. The World Health Organization (WHO) states that non-English languages and cultures use different words for sexual activity, "with slightly different meanings". Various vulgarisms , slang , and euphemisms are used for sexual intercourse or other sexual activity, such as fuck , screw , shag , and

4700-407: The woman on top position or the coital alignment technique , a technique combining the "riding high" variation of the missionary position with pressure-counterpressure movements performed by each partner in rhythm with sexual penetration, to maximize clitoral stimulation. Anal sex involves stimulation of the anus , anal cavity, sphincter valve or rectum ; it most commonly means the insertion of

4800-736: The "widespread, unquestioned equation of penile–vaginal intercourse with sex reflects a failure to examine systematically 'whether the respondent's understanding of the question [about sexual activity] matches what the researcher had in mind'". This focus can also relegate other forms of mutual sexual activity to foreplay or contribute to them not being regarded as "real sex", and limits the meaning of rape . It may also be that conceptually conflating sexual activity with vaginal intercourse and sexual function hinders and limits information about sexual behavior that non-heterosexual people may be engaging in, or information about heterosexuals who may be engaging in non–vaginal sexual activity. Studies regarding

4900-468: The 'main event'" and that "because women reach orgasm through intercourse less consistently than men," they are likelier than men to fake an orgasm to satisfy their sexual partners. In 1991, scholars from the Kinsey Institute stated, "The truth is that the time between penetration and ejaculation varies not only from man to man, but from one time to the next for the same man." They added that

5000-487: The French Institut national d'études démographiques conducted a cross-cultural study titled "At what age do women and men have their first sexual intercourse?" In the first group of the contemporary cultures he studied, which included sub-Saharan Africa (listing Mali , Senegal and Ethiopia ), the data indicated that the age of men at sexual initiation in these societies is at later ages than that of women, but

5100-618: The LMP-to-ovulation is 8.2 to 20.5 days. The average time to birth has been estimated to be 268 days (38 weeks and two days) from ovulation , with a standard deviation of 10 days or coefficient of variation of 3.7%. Fertilization age is sometimes used postnatally (after birth) as well to estimate various risk factors. For example, it is a better predictor than postnatal age for risk of intraventricular hemorrhage in premature babies treated with extracorporeal membrane oxygenation . Various disorders can arise from defects in

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5200-793: The Philippines, fertility awareness and the rhythm method are emphasized while disapproval is expressed with regard to other contraceptive methods. Worldwide, sterilization is a more common birth control method, and use of the intrauterine device (IUD) is the most common and effective way of reversible contraception. Conception and contraception are additionally a life-and-death situation in developing countries , where one in three women give birth before age 20; however, 90% of unsafe abortions in these countries could be prevented by effective contraception use. The National Survey of Sexual Health and Behavior (NSSHB) indicated in 2010 that "1 of 4 acts of vaginal intercourse are condom-protected in

5300-637: The U.S. (1 in 3 among singles)," that "condom use is higher among black and Hispanic Americans than among white Americans and those from other racial groups," and that "adults using a condom for intercourse were just as likely to rate the sexual extent positively in terms of arousal, pleasure and orgasm than when having intercourse without one". Penile–vaginal penetration is the most common form of sexual intercourse. Studies indicate that most heterosexual couples engage in vaginal intercourse nearly every sexual encounter. The National Survey of Sexual Health and Behavior (NSSHB) reported in 2010 that vaginal intercourse

5400-456: The appropriate length for sexual intercourse is the length of time it takes for both partners to be mutually satisfied, emphasizing that Kinsey "found that 75 percent of men ejaculated within two minutes of penetration. But he didn't ask if the men or their partners considered two minutes mutually satisfying" and "more recent research reports slightly longer times for intercourse". A 2008 survey of Canadian and American sex therapists stated that

5500-405: The average time for heterosexual intercourse (coitus) was 7 minutes and that 1 to 2 minutes was too short, 3 to 7 minutes was adequate and 7 to 13 minutes desirable, while 10 to 30 minutes was too long. Anorgasmia is regular difficulty reaching orgasm after ample sexual stimulation, causing personal distress. This is significantly more common in women than in men, which has been attributed to

5600-608: The body's production of antibodies and subsequent lower blood pressure , and decreased risk of prostate cancer . Sexual intimacy and orgasms increase levels of the hormone oxytocin (also known as "the love hormone"), which can help people bond and build trust. Oxytocin is believed to have a more significant impact on women than on men, which may be why women associate sexual attraction or sexual activity with romance and love more than men do. A long-term study of 3,500 people between ages 18 and 102 by clinical neuropsychologist David Weeks indicated that, based on impartial ratings of

5700-416: The decades since the mnemonic was developed, further epidemiology has found the incidence of symptomatic diverticulae to be 4%, not 2%, and the incidence to be 2–5x greater in males than females, but the mnemonic is still helpful. Fertilization age Human fertilization is the union of an egg and sperm , occurring primarily in the ampulla of the fallopian tube . The result of this union leads to

5800-485: The deposit of (usually) raw semen in the vagina of a woman, is in effect a substitute for intercourse and is often contrasted with 'normal intercourse' in this context. Reproductive methods also extend to gay and lesbian couples. For gay male pairings, there is the option of surrogate pregnancy; for lesbian couples, there is donor insemination in addition to choosing surrogate pregnancy. Some women use artificial insemination to become single mothers by choice . There are

5900-415: The digital manipulation of the clitoris, rest of the vulva , vagina or anus for the purpose of sexual arousal and sexual stimulation; it may constitute the entire sexual encounter or it may be part of mutual masturbation, foreplay or other sexual activities. Natural human reproduction involves penile–vaginal penetration, during which semen , containing male gametes known as sperm cells or spermatozoa,

6000-410: The disease , and patients can enjoy healthy and productive lives. In cases where infection is suspected, early medical intervention is highly beneficial in all cases. The CDC stated "the risk of HIV transmission from an infected partner through oral sex is much less than the risk of HIV transmission from anal or vaginal sex," but that "measuring the exact risk of HIV transmission as a result of oral sex

6100-510: The disorder, estimates for the prevalence of premature ejaculation vary significantly more than for erectile dysfunction. For example, the Mayo Clinic states, "Estimates vary, but as many as 1 out of 3 men may be affected by [premature ejaculation] at some time." Further, "Masters and Johnson speculated that premature ejaculation is the most common sexual dysfunction, even though more men seek therapy for erectile difficulties" and that this

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6200-445: The embryo or fetus. The resultant age is known as fertilization age , fertilizational age , conceptional age , embryonic age , fetal age or (intrauterine) developmental (IUD) age . Gestational age , in contrast, takes the beginning of the last menstrual period (LMP) as the start point. By convention, gestational age is calculated by adding 14 days to fertilization age and vice versa. Fertilization though usually occurs within

6300-529: The epidemic. Of the 2.7 million new HIV infections estimated to occur worldwide in 2010, 1.9 million (70%) were in Africa . The World Health Organization also stated that the "estimated 1.2 million Africans who died of HIV-related illnesses in 2010 comprised 69% of the global total of 1.8 million deaths attributable to the epidemic." It is diagnosed by blood tests , and while no cure has been found, it can be controlled by management through antiretroviral drugs for

6400-452: The expression of a gene transcription factor called ΔFosB (delta FosB) in the brain's reward center ; consequently excessively frequent engagement in sexual activity on a regular (daily) basis can lead to the overexpression of ΔFosB, inducing an addiction to sexual activity. Sexual addiction or hypersexuality is often considered an impulse control disorder or a behavioral addiction. It has been linked to atypical levels of dopamine,

6500-550: The female is in estrus, and to engage in sex acts with same-sex partners . Like humans engaging in sexual activity primarily for pleasure, this behavior in these animals is also presumed to be for pleasure, and a contributing factor to strengthening their social bonds. Sexual intercourse may be called coitus , copulation , coition , or intercourse . Coitus is derived from the Latin word coitio or coire , meaning "a coming together or joining together" or "to go together", and

6600-431: The female's reproductive tract in non-vaginal ways among the animals, such as by cloacal copulation. For most non-human mammals , mating and copulation occur at the point of estrus (the most fertile period of time in the female's reproductive cycle), which increases the chances of successful impregnation . However, bonobos , dolphins and chimpanzees are known to engage in sexual intercourse regardless of whether

6700-448: The fertile window, a practice that is sometimes called 'timed intercourse'. Timed intercourse using urine tests that predict ovulation may help improve the rate of pregnancy and live births for some couples trying to conceive such as those who have been trying for less than 12-months and who are under 40 years old, however, it is not clear from medical evidence if timed intercourse improves the rate of ultra-sound confirmed pregnancies and it

6800-426: The fertilization process. Whether that results in the process of contact between the sperm and egg, or the state of health of the biological parent carrying the zygote cell. The following are a few of the diseases that can occur and be present during the process. Sexual intercourse Sexual intercourse (also coitus or copulation ) is a sexual activity typically involving the insertion and thrusting of

6900-408: The formation of the male pronucleus. This is why all mitochondria in humans are of maternal origin. Still, a considerable amount of RNA from the sperm is delivered to the resulting embryo and likely influences embryo development and the phenotype of the offspring. The sperm nucleus then fuses with the ovum, enabling fusion of their genetic material. When the sperm enters the perivitelline space ,

7000-461: The fusion of their genetic material both the oocyte and the sperm undergo transformations as a reaction to the fusion of cell membranes. The oocyte completes its second meiotic division . This results in a mature haploid ovum and the release of a polar body. The nucleus of the oocyte is called a pronucleus in this process, to distinguish it from the nuclei that are the result of fertilization. The sperm's tail and mitochondria degenerate with

7100-402: The head of a sperm. The human ova was first observed in 1827 by Karl Ernst von Baer . Only in 1876 did Oscar Hertwig prove that fertilization is due to fusion of an egg and sperm cell. Fertilization occurs in the ampulla of the fallopian tube , the section that curves around the ovary. Capacitated sperm are attracted to progesterone, which is secreted from the cumulus cells surrounding

7200-645: The lack of sex education with regard to women's bodies, especially in sex-negative cultures, such as clitoral stimulation usually being key for women to orgasm. The physical structure of coitus favors penile stimulation over clitoral stimulation; the location of the clitoris then usually necessitates manual or oral stimulation in order for the woman to achieve orgasm. Approximately 25% of women report difficulties with orgasm, 10% of women have never had an orgasm, and 40% or 40–50% have either complained about sexual dissatisfaction or experienced difficulty becoming sexually aroused at some point in their lives. Vaginismus

7300-473: The lack of a knowledgeable healthcare provider trained and experienced in counseling those with intellectual disabilities on sexual intercourse. Those with intellectual disabilities may have hesitations regarding the discussion of the topic of sex, a lack of sexual knowledge and limited opportunities for sex education. In addition there are other barriers such as a higher prevalence of sexual abuse and assault. These crimes often remain underreported. There remains

7400-410: The male penis inside the female vagina for sexual pleasure , reproduction , or both. This is also known as vaginal intercourse or vaginal sex . Sexual penetration has been known by humans since the dawn of time, and has been an instinctive form of sexual behaviour and psychology among humans. Other forms of penetrative sexual intercourse include anal sex (penetration of the anus by

7500-437: The male and female together. Thus, the first mitosis of the union of sperm and oocyte is the actual fusion of their chromosomes. Each of the two daughter cells resulting from that mitosis has one replica of each chromatid that was replicated in the previous stage. Thus, they are genetically identical. Fertilization is the event most commonly used to mark the beginning point of life, in descriptions of prenatal development of

7600-621: The meaning of sexual intercourse sometimes come into conflict. While most consider penile–vaginal intercourse to be sex, whether anal or oral intercourse are considered sex is more debatable, with oral sex ranking lowest. The Centers for Disease Control and Prevention (CDC) stated that "although there are only limited national data about how often adolescents engage in oral sex, some data suggest that many adolescents who engage in oral sex do not consider it to be 'sex'; therefore they may use oral sex as an option to experience sex while still, in their minds, remaining abstinent". Upton et al. stated, "It

7700-490: The oocyte. Progesterone binds to the CatSper receptor on the sperm membrane and increases intracellular calcium levels, causing hyperactive motility. The sperm will continue to swim towards higher concentrations of progesterone, effectively guiding it to the oocyte. Around 200 out of 200 million spermatozoa reach the ampulla. At the beginning of the process, the sperm undergoes a series of changes, as freshly ejaculated sperm

7800-410: The other half Y chromosome ). Their membranes dissolve, leaving no barriers between the male and female chromosomes . During this dissolution, a mitotic spindle forms between them. The spindle captures the chromosomes before they disperse in the egg cytoplasm. Upon subsequently undergoing mitosis (which includes pulling of chromatids towards centrioles in anaphase) the cell gathers genetic material from

7900-416: The outside of the secondary oocyte . The corona radiata sends out chemicals that attract the sperm in the fallopian tube to the oocyte. It lies above the zona pellucida, a membrane of glycoproteins that surrounds the oocyte. Where the spermatozoan is about to pierce, the yolk ( ooplasm ) is drawn out into a conical elevation, termed the cone of attraction or reception cone. Once the spermatozoon has entered,

8000-569: The ovum, forming a new embryo . Pregnancy begins after the fertilized ovum is implanted in the lining of the uterus (the endometrium ). Pregnancy rates for sexual intercourse are highest during the menstrual cycle time from some five days before until approximately one day after ovulation (this is sometimes called the fertile window ). For optimal pregnancy chance, there are recommendations of vaginal intercourse every one or two days, or every two or three days. Some people who are trying to conceive may choose to time vaginal intercourse with

8100-618: The partners orient their hips to allow the penis to move back and forth in the vagina to cause friction, typically without fully removing the penis. In this way, they stimulate themselves and each other, often continuing until orgasm in either or both partners is achieved. For human females, stimulation of the clitoris plays a significant role in sexual activity; 70–80% of women require direct clitoral stimulation to achieve orgasm, though indirect clitoral stimulation (for example, via vaginal intercourse) may also be sufficient (see orgasm in females ). Because of this, some couples may engage in

8200-622: The penis), oral sex (penetration of the mouth by the penis or oral penetration of the female genitalia ), fingering (sexual penetration by the fingers) and penetration by use of a dildo (especially a strap-on dildo ), and vibrators . These activities involve physical intimacy between two or more people and are usually used among humans solely for physical or emotional pleasure. They can contribute to human bonding . There are different views on what constitutes sexual intercourse or other sexual activity, which can impact on views of sexual health . Although sexual intercourse , particularly

8300-456: The peripheral portion of the yolk changes into a membrane, the perivitelline membrane, which prevents the passage of additional spermatozoa. After binding to the corona radiata the sperm reaches the zona pellucida , which is an extracellular matrix of glycoproteins . A ZP3 glycoprotein on the zona pellucida binds to a receptor on the cell surface of the sperm head. This binding triggers the acrosome to burst, releasing acrosomal enzymes that help

8400-698: The phrase "sleep together". The laws of some countries use the euphemism, carnal knowledge . Penetration of the vagina by the erect penis is additionally known as intromission , or by the Latin name immissio penis (Latin for "insertion of the penis"). The age of first sexual intercourse is called sexarche . Vaginal, anal and oral sex are recognized as sexual intercourse more often than other sexual behaviors. Sexual activity that does not involve penile-vaginal sex or other sexual penetration might be used to retain virginity (sometimes called technical virginity ) or labeled outercourse . One reason virginity loss

8500-445: The presence of other STIs. In 2005, the World Health Organization estimated that 123 million women become pregnant worldwide each year, and around 87 million of those pregnancies or 70.7% are unintentional. Approximately 46 million pregnancies per year reportedly end in induced abortion . Approximately 6 million U.S. women become pregnant per year. Out of known pregnancies, two-thirds result in live births and roughly 25% in abortions;

8600-586: The production of a fertilized egg called a zygote , initiating embryonic development . Scientists discovered the dynamics of human fertilization in the 19th century. The process of fertilization involves a sperm fusing with an ovum. The most common sequence begins with ejaculation during copulation , follows with ovulation , and finishes with fertilization. Various exceptions to this sequence are possible, including artificial insemination , in vitro fertilization , external ejaculation without copulation, or copulation shortly after ovulation. Upon encountering

8700-403: The protection of a condom is often associated with emasculation because condoms prevent direct penile–to–skin genital contact. Sexual intercourse or other sexual activity can encompass various sexually stimulating factors ( physiological stimulation or psychological stimulation ), including different sex positions (such as the missionary position , the most common human sex position ) or

8800-564: The remainder end in miscarriage. However, many more women become pregnant and miscarry without even realizing it, instead mistaking the miscarriage for an unusually heavy menstruation . The U.S. teenage pregnancy rate fell by 27 percent between 1990 and 2000, from 116.3 pregnancies per 1,000 girls aged 15–19 to 84.5. This data includes live births, abortions, and fetal losses. Almost 1 million American teenage women, 10% of all women aged 15–19 and 19% of those who report having had intercourse, become pregnant each year. Sexual activity can increase

8900-459: The secondary oocyte , the acrosome of the sperm produces enzymes which allow it to burrow through the outer shell called the zona pellucida of the egg. The sperm plasma then fuses with the egg's plasma membrane and their nuclei fuse, triggering the sperm head to disconnect from its flagellum as the egg travels down the fallopian tube to reach the uterus. In vitro fertilization (IVF) is a process by which egg cells are fertilized by sperm outside

9000-491: The secondary oocyte fuse with the plasma membrane of the cell, causing enzymes inside these granules to be expelled by exocytosis to the zona pellucida. This in turn causes the glycoproteins in the zona pellucida to cross-link with each other — i.e. the enzymes cause the ZP2 to hydrolyse into ZP2f — making the whole matrix hard and impermeable to sperm. This prevents fertilization of an egg by more than one sperm. In preparation for

9100-417: The sperm penetrate through the thick zona pellucida layer surrounding the oocyte, ultimately gaining access to the egg's cell membrane. Some sperm cells consume their acrosome prematurely on the surface of the egg cell, facilitating the penetration by other sperm cells. As a population, mature haploid sperm cells have on average 50% genome similarity, so the premature acrosomal reactions aid fertilization by

9200-440: The subjects' photographs, sex on a regular basis is associated with people looking significantly chronologically younger. However this does not imply causality. Vaginal intercourse for the first time increases vaginal immune activity. Sexually transmitted infections (STIs) are bacteria , viruses or parasites that are spread by sexual contact, especially vaginal, anal, or oral intercourse, or unprotected sex . Oral sex

9300-906: The term coitus, generally denotes penile–vaginal penetration and the possibility of creating offspring , it also commonly denotes penetrative oral sex and penile–anal sex, especially the latter. It usually encompasses sexual penetration, while non-penetrative sex has been labeled outercourse , but non-penetrative sex may also be considered sexual intercourse. Sex , often a shorthand for sexual intercourse , can mean any form of sexual activity. Because people can be at risk of contracting sexually transmitted infections during these activities, safer sex practices are recommended by health professionals to reduce transmission risk. Various jurisdictions place restrictions on certain sexual acts, such as adultery , incest , sexual activity with minors , prostitution , rape , zoophilia , sodomy , premarital sex and extramarital sex . Religious beliefs also play

9400-446: The unnecessary use of these drugs because they are accompanied by serious risks such as increased chance of heart attack. The selective serotonin reuptake inhibitor (SSRI) and antidepressant drug dapoxetine has been used to treat premature ejaculation. In clinical trials, those with PE who took dapoxetine experienced sexual intercourse three to four times longer before orgasm than without the drug. Another ejaculation-related disorder

9500-433: The use of sex toys . Foreplay may precede some sexual activities, often leading to sexual arousal of the partners and resulting in the erection of the penis or natural lubrication of the vagina . It is also common for people to be as sexually satisfied by being kissed, touched erotically , or held as they are during sexual intercourse. Non- primate females copulate only when in estrus , but sexual intercourse

9600-506: The use of vaginal dilators . Additionally, the use of Botox as a medical treatment for vaginismus has been tested and administered. Painful or uncomfortable sexual intercourse may also be categorized as dyspareunia . Approximately 40% of males reportedly have some form of erectile dysfunction (ED) or impotence, at least occasionally. Premature ejaculation has been reported to be more common than erectile dysfunction, although some estimates suggest otherwise. Due to various meanings of

9700-420: The womb, in vitro . Fertilization was not understood in antiquity. Hippocrates believed that the embryo was the product of male semen and a female factor. But Aristotle held that only male semen gave rise to an embryo, while the female only provided a place for the embryo to develop, a concept he acquired from the preformationist Pythagoras . Aristotle argued for form and function emerging gradually, in

9800-412: The zona pellucida. These two blocks of polyspermy are what prevent the zygote from having too much DNA. The pronuclei migrate toward the center of the oocyte, rapidly replicating their DNA as they do so to prepare the zygote for its first mitotic division. Usually 23 chromosomes from spermatozoon and 23 chromosomes from egg cell fuse (approximately half of spermatozoons carry X chromosome and

9900-892: Was lower, with both men and women involved in sexual intercourse before any union formation; the study listed Switzerland, Germany and the Czech Republic as members of this group. Concerning United States data, tabulations by the National Center for Health Statistics report that the age of first sexual intercourse was 17.1 years for both males and females in 2010. The CDC stated that 45.5 percent of girls and 45.7 percent of boys had engaged in sexual activity by 19 in 2002; in 2011, reporting their research from 2006 to 2010, they stated that 43% of American unmarried teenage girls and 42% of American unmarried teenage boys have ever engaged in sexual intercourse. The CDC also reports that American girls will most likely lose their virginity to

10000-594: Was more closely matched; there were two sub-groups, however. In non-Latin, Catholic countries (Poland and Lithuania are mentioned), age at sexual initiation was higher, suggesting later marriage and reciprocal valuing of male and female virginity. The same pattern of late marriage and reciprocal valuing of virginity was reflected in Singapore and Sri Lanka . The study considered China and Vietnam to also fall into this group, though data were not available. In northern and eastern European countries, age at sexual initiation

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