Sexual Intercourse

Illustration showing cross section of male and female reproductive systems during sexual intercourse

The purpose of sexual intercourse (coitus is the medical term, copulation the scientific one) is to produce a baby and perpetuate one’s genes. However humans also have sex because it feels good. In the Western world people reproduce on average no more than two or three times in their lives, but they will probably engage in sexual intercourse thousands of times.

Sex is actually good for you. Having sex once or twice a week increases the level of immunoglobulin A in the blood, which protects against many infections, but daily sex reduces the level of immunoglobulin A to levels below those in people who totally abstain.

Intercourse consists of the man inserting his penis into the woman’s vagina. Before he does this, ideally each partner will become sexually aroused. In the man this means that the penis will become engorged with blood so that it becomes larger, stiff and erect. In the woman, the vagina lengthens and glands in the vagina produce a lubricating fluid, which enables the man’s penis to slide in easily. Thrusting movements by both partners stimulate the penis and vagina, producing pleasurable sensations that increase in intensity until a climax or orgasm is reached. In a woman an orgasm consists of contractions of the vagina and the man will have an ejaculation of semen, which is a mix of seminal fluid and sperm.

Positions for intercourse vary. The commonest is the so-called missionary position in which the woman lies on her back with her legs bent up and the man lies on top of her. Penetration is generally deepest in this position.

In a man, orgasm and ejaculation go together. One usually does not occur without the other. Consequently a man has to have an orgasm before he can father a child. The situation is different in women. A woman does not need to have an orgasm to conceive and some women who have active sex lives rarely or never achieve orgasm.

Statistically, 85% of menstruating women will fall pregnant within one year if undertaking sexual intercourse at least once a week.

The final point to note about sex is that the “battle of the sexes” will never be won, because although men desire sex far more often than women, the majority of women enjoy sex far more than men.

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