Semen

Basic Information

Semen is an organic fluid, also known as seminal fluid, that usually contains spermatozoa. It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals and can fertilize female ova. The process of discharge is called ejaculation.

During the process of ejaculation, sperm passes through the ejaculatory ducts and mixes with fluids from the seminal vesicles, the prostate, and the bulbourethral glands to form the semen. The seminal vesicles produce a yellowish viscous fluid rich in fructose and other substances that makes up about 70% of human semen. The prostatic secretion, influenced by dihydrotestosterone, is a whitish (sometimes clear), thin fluid containing proteolytic enzymes, citric acid, acid phosphatase and lipids. The bulbourethral glands secrete a clear secretion into the lumen of the urethra to lubricate it.

Sertoli cells, which nurture and support developing spermatocytes, secrete a fluid into seminiferous tubules that helps transport sperm to the genital ducts. The ductuli efferentes possess cuboidal cells with microvilli and lysosomal granules that modify the semen by reabsorbing some fluid. Once the semen enters the ductus epididymis the principle cells, which contain pinocytotic vessels indicating fluid reabsorption, secrete glycerophosphocholine which most likely inhibits premature capacitation. The accessory genital ducts, the seminal vesicle, prostate glands, and the bulbourethral glands, produce most of the seminal fluid.

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, as 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, and protect DNA inside the sperm from acidic denaturation.

Appearance and Consistency

Most semen is white in color, but grey or even yellowish semen can be normal as well. Blood in the semen, hematospermia, can cause a pink or reddish color and may indicate a medical problem which should be evaluated by a doctor.

After ejaculation, semen first goes through a clotting process, then becomes more liquid. It is postulated that the initial clotting helps keep the semen in the vaginal canal, but liquefaction frees the sperm to make their long journey to the ova. Immediately after ejaculation, semen is typically a sticky, jelly-like liquid often forming globules. Within five to forty minutes, it will become more watery and liquid before finally drying.

Semen as an Anti-Depressant

Research has suggested that semen may have anti-depressant properties. In studies, women who did not use condoms but instead absorbed semen vaginally sustained a better mood. Research has not demonstrated that the semen is the cause or simply correlates with the ultimate cause of the difference in mood between women who use condoms and those that do not.[5][6]

Transmission of Disease

Semen can be the vehicle for many sexually transmitted diseases, including HIV, the virus that causes AIDS.

It is also hypothesized that components of semen, such as the spermatozoa as well as the seminal plasma, can cause immunosuppression in the body when introduced to the bloodstream or lymph.[citation needed] Evidence for this dates back to 1898, when Elie Metchnikoff injected a guinea pig with its own and foreign guinea pig sperm, finding that an antibody was produced in response; however the antibody was inactive, pointing to a suppression response by the immune system.[citation needed]

Further research, such as that by Mathur and Goust, demonstrated that non-preexisting antibodies were produced in humans in response to the sperm. These antibodies mistakenly recognized native T lymphocytes as foreign antigens, and consequently T lymphocytes would fall under attack by the body's B lymphocytes.

Other semen components are shown to spur an immunosuppressive effect are seminal plasma and seminal lymphocytes. Semen contains proteins with potent bactericidal activity but these proteins are not active against Neisseria gonorrhoeae a common cause of sexually transmitted disease.

Semen allergy

In rare cases, people have been known to experience allergic reactions to seminal fluids, known as human seminal plasma hypersensitivity. Symptoms can be localized or systemic  and may include vaginal itching, redness, swelling, or blisters within 30 minutes of contact. They may also include generalized itching, hives, and even difficulty breathing.

The best way to test for human seminal plasma sensitivity is to use a condom during intercourse. If symptoms dissipate with the use of a condom, it is possible that a sensitivity to semen is present. Mild cases can often be overcome by repeated, incremental exposure. In more severe cases, it is important to seek the advice of a physician, particularly when a couple is trying to conceive. (In some cases, artificial insemination may be required.)