Semen: Encyclopedia II - Semen - Composition of human semen

Semen - Composition of human semen

Approximately 200- to 500-million spermatozoa (also called sperm or spermatozoans), produced in the testes, are released per ejaculation. However, they make up only about 2–5% of the volume of semen. The bulk of the semen is composed of seminal plasma, the fluid portion of semen. This fluid is contributed by the accessory male reproductive organs. Some 60% of the volume of ejaculate is produced by the seminal vesicles, and most of the remainder is generated by the prostate. A small amount of viscous mucus secreted by the bulbourethral glands contributes to the cohesive jelly-like texture of semen.

Seminal plasma of humans contains a complex range of organic and inorganic constituents. They include metal and salt ions, sugars, lipids, steroid hormones, enzymes, prostaglandin hormones, amino acids and basic amines. The seminal plasma provides a nutritive and protective medium for the spermatozoa during their journey through the female reproductive tract. The normal environment of the vagina is a hostile one for sperm cells, for it is very acidic (from the native microflora producing lactic acid), viscous, and patrolled by immune cells. The components in the seminal plasma attempt to compensate for this hostile environment.

Basic amines such as putrescine, spermine, spermidine and cadaverine are responsible for the smell and flavor of semen. These alkaline bases counteract the acidic environment of the vaginal canal (which is harmful to sperm), and protect DNA inside the sperm from acidic denaturation. Salts and metal ions in the semen help to create a more hospitable environment for the sperm in the vaginal canal. A typical ejaculation can contain up to 5 mg of zinc. Zinc serves to help to stabilize the DNA-containing chromatin in the sperm cells. A zinc deficiency may result in lowered fertility because of increased sperm fragility. Zinc deficiency can also adversely affect spermatogenesis.

The simple sugar fructose is the main energy source of sperm cells, which rely entirely on sugars from the seminal plasma for energy. Other components of semen (mucus and texturizing proteins) serve to increase the mobility of sperm cells in the vagina and cervix by creating a less viscous channel for the sperm cells to swim through, and preventing their diffusion out of the semen. Prostaglandin hormones are involved in suppressing an immune response by the female against the foreign semen.

Adapted from the Wikipedia article "Composition of human semen", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki