reproduction in human beings..........................

 sexual reproduction in human beings

Sexual intercourse (or coitus or copulation) is, broadly, the insertion and thrusting of a male's penis, usually when erect, into a female's vagina for the purposes of sexual pleasure or reproduction; also known as vaginal intercourse or vaginal sex. Other forms of penetrative sexual intercourse include penetration of the anus by the penis (anal sex), penetration of the mouth by the penis or oral penetration of the vulva or vagina (oral sex), sexual penetration by the fingers (fingering), and sexual penetration by use of a strap-on dildo. These activities involve physical intimacy between two or more individuals and are usually used among humans solely for physical or emotional pleasure and commonly contribute to human bonding.A variety of views concern what constitutes sexual intercourse or other sexual activity and their effects on health. While the term sexual intercourse, particularly the variant coitus, most commonly denotes penile-vaginal penetration and the possibility of creating offspring (the fertilization process known as reproduction), oral sex (especially when penetrative) and particularly penile-anal sex are also commonly considered sexual intercourse. Non-penetrative sex acts (such as non-penetrative forms of cunnilingus or mutual masturbation) have been termed outercourse, but may additionally be among the sexual acts contributing to human bonding and considered sexual intercourse The term 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, though the transmission risk is significantly reduced during non-penetrative sex,safe sex practices are advised.

Health effects

Benefits

In humans, sexual intercourse and sexual activity in general have been reported to produce health benefits as varied as improved sense of smell, stress and blood pressure reduction,increased immunity, and decreased risk of prostate cancer. 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. Sexual intercourse and sexual activity in general are aspects of many mood repair strategies, which mean they can be used to help dissipate feelings of sadness or depression.

Risks

Sexually transmitted infections (STIs) can be spread by person-to-person sexual contact, especially penetrative sexual intercourse. There are 19 million new cases of sexually transmitted infections every year in the U.S., and, in 2005, the World Health Organization estimated that 448 million people aged 15–49 were being infected a year with curable STIs (such as syphilis, gonorrhea and chlamydia).
STIs are caused by bacteria, viruses and parasites, which are passed from person to person during sexual contact. Some, in particular HIV and syphilis, can also be passed in other ways, including from mother to child during pregnancy and childbirth, through blood products, and by shared hypodermic needles. Gonococcal or chlamydial infections often produce no symptoms. Untreated chlamydial infection can lead to female infertility and ectopic pregnancy. Human papillomavirus can lead to genital and cervical cancers. Syphilis can result in stillbirths and neonatal deaths. Untreated gonococcal infections result in miscarriages, preterm births and perinatal deaths. Infants born to mothers with untreated gonorrhoea or chlamydia can develop neonatal conjunctivitis (a serious eye infection), which can lead to blindness. Hepatitis B can also be transmitted through sexual contact. Globally, there are about 350 million chronic carriers of hepatitis B.

Social effects

Adults

Some researchers, such as Alex Comfort, posit three potential advantages of sexual intercourse in humans, which are not mutually exclusive: reproductive, relational, and recreational. While the development of the birth-control pill and other highly effective forms of contraception in the mid- and late 20th century increased people's ability to segregate these three functions, they still overlap a great deal and in complex patterns. For example: A fertile couple may have sexual intercourse while contracepting not only to experience sexual pleasure (recreational), but also as a means of emotional intimacy (relational), thus deepening their bonding, making their relationship more stable and more capable of sustaining children in the future (deferred reproductive). This couple may emphasize different aspects of sexual intercourse on different occasions, being playful during one episode of sexual intercourse (recreational), experiencing deep emotional connection on another occasion (relational), and later, after discontinuing contraception, seeking to achieve pregnancy (reproductive, or more likely reproductive and relational).

Adolescents

With regard to adolescent sexuality, sexual intercourse is usually for relational and recreational purposes as well. However, teenage pregnancy is often disparaged, and research suggests that the earlier onset of puberty for children puts pressure on children and teenagers to act like adults before they are emotionally or cognitively ready,and thus are at risk to suffer from emotional distress as a result of their sexual activities. Some studies have concluded that engaging in sexual activity leaves adolescents, especially girls, with higher levels of stress and depression. A majority of adolescents in the United States have been provided with some information regarding sexuality,though there have been efforts among social conservatives in the United States government to limit sex education in public schools to abstinence-only sex education curricula.