Semen

Semen or ejaculate is the fluid discharged through the penis during ejaculation, usually at the time of orgasm. During vaginal intercourse, it carries sperm into the female, sometimes resulting in pregnancy. Semen is a whitish, milky fluid, slightly viscous, containing water and small amounts of salt, protein, and fructose sugar, and is in itself harmless on the skin or if swallowed. However, semen can be the vehicle for many sexually transmitted diseases, including HIV, the virus that causes AIDS. Any kind of sexual or other skin contact with the semen of a person infected with HIV should be avoided, even by persons already infected with the virus, as this may cause harmful re-infection.

Composition

Spermatozoa (or sperm, for short) are produced in the testicles. They make up only about 2–5% of the volume of semen. Some 60% of semen is produced by the seminal vesicles, and most of the rest by the prostate. A small amount of viscous mucus comes from the bulbourethral glands.

Fructose is the main energy source of sperm cells. Some of the other components of semen serve to increase the mobility of sperm cells. Sperm function best in a slightly alkaline environment, whereas the vagina is usually slightly acidic. The fluid excreted by the seminal vesicles is alkaline.

Men lose up to 5 mg of zinc when they ejaculate. The zinc comes from the prostate gland. Men that ejaculate frequently might become deficient in zinc. Zinc deficiency can also cause reproductive problems and problems with spermatogenesis.

Pregnancy

All sexual behaviors that result in the contact of semen with the vagina or vulva may result in pregnancy at any time unless adequate contraceptive measures (birth control) are in force. No form of birth control (except for total abstinence or a successful sterilization) protects a woman entirely from pregnancy; for example condoms used perfectly are approximately 97% effective against pregnancy over one year (i.e. 3 out of 100 women will become pregnant in this time). "Unprotected" sexual intercourse (that is, sex without the use of contraceptives) between a biological male and female is generally the most effective cause of pregnancy. When a male is sexually excited, a small amount of a clear fluid (pre-ejaculate) may leak out of the penis before orgasm and ejaculation. One reason that coitus interruptus ("withdrawal" of the penis from the vagina just before the ejaculation of the penis) is not a very effective contraceptive method during heterosexual intercourse is that this pre-ejaculate fluid may also contain sperm.

Cultural Views

In some cultures, semen is attributed with special properties of masculinity. For instance, among the Etoro people of Papua New Guinea, it is believed that young boys must fellate and ingest the sperm of their elders to achieve proper sexual maturation. Other cultures believe semen to have beneficial qualities when applied to the skin, mainly for cosmetic purposes.

See also

• Sexual slang for a list various commonly used terms for semen