Sex

Sexual intercourse or sex, also known as copulation or coitus, commonly refers to the act in which the male reproductive organ enters the female reproductive tract. The two entities may be of opposite sexes or not, or they may be hermaphroditic, as is the case with snails. In recent years, penetration of non-sexual organs (oral intercourse, anal intercourse) or by non-sexual organs (fingering, fisting) are also sometimes included in this definition. Traditionally, intercourse has been viewed as the natural endpoint of all sexual contact between a man and a woman.

Non-penetrative sexual contacts (oral sex may or may not be penetrative) and mutual masturbation have been referred to as "outercourse". "Outercourse" is something of a misnomer, as it contrasts "outer" with "inter" but the "inter" in "intercourse" means "between two people" or beings. It does not describe being inside or outside of the body. The word sex, in the context of sexual intimacy, is often, if not universally, understood to include any mutual genital stimulation, i.e. both intercourse and outercourse.

Mating is the term most often used to refer to sexual intercourse between animals other than humans; for most, mating occurs 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 even when the female is not in estrus, and to engage in sex acts with same-sex partners. In most instances, humans have sex primarily for pleasure. This behavior in the above mentioned animals is also presumed to be for pleasure, which in turn strengthens social bonds.


In humans

Vaginal sexual intercourse, also called coitus, is the human form of copulation. While a purpose and effect is reproduction, it is often performed exclusively for pleasure and/or as an expression of love and emotional intimacy. Sexual intercourse typically plays a powerful bonding role; in many societies it is normal for couples to have frequent intercourse while using birth control, sharing pleasure and strengthening their emotional bond through sex even though they are deliberately avoiding pregnancy.

Sexual intercourse may also be defined as referring to other forms of insertive sexual behavior, such as oral sex and anal intercourse. The phrase to have sex can mean any or all of these behaviors, as well as other non-penetrative sex acts not considered here.

Coitus may be preceded by foreplay, which leads to sexual arousal of the partners, resulting in the erection of the penis and natural lubrication of the vagina. To engage in coitus, the erect penis is inserted into the vagina and one or both of the partners move their hips to move the penis backward and forward inside 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. Penetration by the hardened erect penis is also known as intromission, or by the Latin name immissio penis (Latin for "insertion of the penis").

Coitus is the basic reproductive method of humans. During ejaculation, which usually accompanies male orgasm, a series of muscular contractions delivers semen containing male gametes known as sperm cells or spermatozoa from the penis into the vagina.

The subsequent route of the sperm from the vault of the vagina is through the cervix and into the uterus, and then into the fallopian tubes. Millions of sperm are present in each ejaculation, to increase the chances of one fertilizing an egg or ovum. When a fertile ovum from the female is present in the fallopian tubes, the male gamete joins with the ovum, resulting in fertilization and the formation of a new embryo. When a fertilized ovum reaches the uterus, it becomes implanted in the lining of the uterus, known as endometrium, and a pregnancy begins.

Unlike most species, human sexual activity is not linked to periods of estrus and can take place at any time during the reproductive cycle, even during pregnancy.


Sex Health benefits

Sex has been claimed to produce health benefits as varied as improved sense of smell, weight loss, stress reduction, increased immunity, and decreased risk of prostate cancer.

Sex between cohabiting partners lowers blood pressure and reduces stress, according to Stuart Brody, professor of psychology at the University of the West of Scotland. Brody's team monitored 24 women and 22 men who were exposed to stressful situations, such as speaking in public and doing verbal arithmetic, and kept records of their sexual activity. The men and women who had penile-vaginal intercourse responded more positively to stress "than those who engaged in other sexual behaviors or abstained". A study by Keith Light of the University of North Carolina went as far as to find a link between "partner hug" and lower blood pressure in women.

Frequent sexual intercourse was held to reduce the risk of the common cold by Carl Charnetski and Francis X. Brennan of Wilkes University in Wilkes-Barre, Pa. These scientists linked frequent sexual intercourse (once or twice a week) to increased production of the antibody called Immunoglobulin A or IgA, which can protect the body from getting colds and other infections. They took samples of saliva, which contain IgA, from 112 college students who reported the frequency of sex they had. The students in the "frequent" group had higher levels of IgA than those in the other three groups, consisting of people who were celibate, had sex less than once a week, or had it "very often" (three or more times weekly). The other three groups had comparable IgA levels. Charnetski and Brennan had previously shown that exposure to elevator music has a similar effect on IgA levels.

"Sex is a great mode of exercise," according to Patti Britton, PhD, past president of the American Association of Sexuality Educators, Counselors and Therapists (AASECT) and currently host of the website "Your Sex Coach". She notes that thirty minutes of sex burns 85 calories or more. She concludes that 42 half-hour sessions, or 21 hour-long sessions, will burn 3,570 calories - sufficient to lose one pound.

"Boosting self-esteem" was one of 237 reasons people have sex, collected by University of Texas researchers and published in the journal Archives of Sexual Behavior. Some subjects who already had high self-esteem said they sometimes have sex to "feel even better".

Sexual intimacy, as well as orgasms, increases levels of the hormone oxytocin, also known as "the love hormone" which helps people bond and build trust. Researchers from the University of Pittsburgh and the University of North Carolina at Chapel Hill evaluated 59 premenopausal women before and after warm contact with their husbands and partners ending with hugs. They found that the more contact, the higher the oxytocin levels. Oxytocin allows people to feel the urge to nurture and to bond. Generosity has also been credited and linked to a higher level of oxytocin. In addition, as the hormone oxytocin surges, endorphins increase, and pain declines. In a study published in the Bulletin of Experimental Biology and Medicine, 48 volunteers who inhaled oxytocin vapor and then had their fingers pricked lowered their pain threshold by more than half. The oxytocin released during orgasm also promotes sleep.

Men who have frequent ejaculations, especially men in their 20s, may reduce their risks of prostate cancer later in life. Australian researchers reported in the British Journal of Urology International that they followed men diagnosed with prostate cancer and those without. They found no association of prostate cancer with the number of sexual partners as the men reached their 30s, 40s, and 50s, but men who had five or more ejaculations weekly while in their 20s reduced their risk of getting prostate cancer later by a third. Another study, reported in the Journal of the American Medical Association, "found that frequent ejaculations, 21 or more a month, were linked to lower prostate cancer risk in older men, as well, compared with less frequent ejaculations of four to seven monthly".

During sex, pelvic floor muscle exercises known as Kegels offer benefits for women. More sexual pleasure is expected to result, strengthening of the area, and help to minimize the risk of incontinence later in life.