Semen, also known as seminal fluid, is an organic fluid that may contain spermatozoa. It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals and can fertilize female ova. In humans, seminal fluid contains several components besides spermatozoa: proteolytic and other enzymes as well as fructose are elements of seminal fluid which promote the survival of spermatozoa and provide a medium through which they can move or "swim".
Semen is produced and originates from the seminal vesicle, which is located in the pelvis. The process that results in the discharge of semen is called ejaculation.
Depending on the species, spermatozoa can fertilize ova externally or internally. In external fertilization, the spermatozoa fertilize the ova directly, outside of the female's sexual organs. Female fish, for example, spawn ova into their aquatic environment, where they are fertilized by the semen of the male fish.
During internal fertilization, however, fertilization occurs inside the female's sexual organs. Internal fertilization takes place after insemination of a female by a male through copulation. In low vertebrates (amphibians, reptiles, birds and monotreme mammals), copulation is achieved through the physical mating of the cloaca of the male and female. In marsupial and placental mammals, copulation occurs through the vagina.
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.
Seminal plasma of humans contains a complex range of organic and inorganic constituents.
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 and buffer the acidic environment of the vaginal canal, and protect DNA inside the sperm from acidic denaturation.
The components and contributions of semen are as follows:
| Gland | Approximate % | Description |
| testes | 2–5% | Approximately 200- to 500-million spermatozoa (also called sperm or spermatozoans), produced in the testes, are released per ejaculation. If a man has undergone a vasectomy, he will have no sperm in the ejaculation. |
| seminal vesicle | 65–75% | amino acids, citrate, enzymes, flavins, fructose (2–5 mg per mL semen, the main energy source of sperm cells, which rely entirely on sugars from the seminal plasma for energy), phosphorylcholine, prostaglandins (involved in suppressing an immune response by the female against the foreign semen), proteins, vitamin C |
| prostate | 25–30% | acid phosphatase, citric acid, fibrinolysin, prostate specific antigen, proteolytic enzymes, zinc (the zinc level is about 135±40 micrograms/ml for healthy men. 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.) |
| bulbourethral glands | < 1% | galactose, mucus (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. Contributes to the cohesive jelly-like texture of semen.), pre-ejaculate, sialic acid |
A 1992 World Health Organization report described normal human semen as having a volume of 2 ml or greater, pH of 7.2 to 8.0, sperm concentration of 20×10 spermatozoa/ml or more, sperm count of 40×10 spermatozoa per ejaculate or more, and motility of 50% or more with forward progression (categories a and b) of 25% or more with rapid progression (category a) within 60 minutes of ejaculation.
A 2005 review of the literature found that the average reported physical and chemical properties of human semen were as follows:
| Property | Per 100mL | In average volume (3.4mL) |
|---|---|---|
| Calcium (mg) | 27.6 | 0.938 |
| Chloride (mg) | 142 | 4.83 |
| Citrate (mg) | 528 | 18.0 |
| Fructose (mg) | 27.6 | 9.25 |
| Glucose (mg) | 102 | 3.47 |
| Lactic acid (g) | 62 | 2.11 |
| Magnesium (mg) | 11 | 0.374 |
| Potassium (mg) | 109 | 3.71 |
| Protein (g) | 5.04 | 0.171 |
| Sodium (mg) | 300 | 10.2 |
| Urea (g) | 45 | 1.53 |
| Zinc (mg) | 16.5 | 0.561 |
| Buffering capacity (β) | 25 | |
| Osmolarity (mOsm) | 354 | |
| pH | 7.7 | |
| Viscosity (cP) | 3–7 | |
| Volume (mL) | 3.4 | |
| Values for average volume have been calculated and rounded to three sig figs. All other values are those given in the review. | ||
Semen is typically translucent with white, grey or even yellowish tint. Blood in the semen can cause a pink or reddish colour, known as hematospermia, and may indicate a medical problem which should be evaluated by a doctor if the symptom persists.
After ejaculation, the latter part of the ejaculated semen coagulates immediately, forming globules, while the earlier part of the ejaculate typically does not. After a period typically ranging from 15 – 30 minutes, Prostate-specific antigen present in the semen causes the decoagulation of the seminal coagulum. It is postulated that the initial clotting helps keep the semen in the vagina, while liquefaction frees the sperm to make their journey to the ova.
A 2005 review found that the average reported viscosity of human semen in the literature was 3–7 cP.
Semen quality is a measure of the ability of semen to accomplish fertilization. Thus, it is a measure of fertility in a man. It is the sperm in the semen that is the fertile component, and therefore semen quality involves both sperm quantity and sperm quality.
The volume of semen ejaculate varies. A review of 30 studies concluded that the average was around 3.4 milliliters (ml), with some studies finding amounts as high as 4.99 ml or as low as 2.3 ml. In a study with Swedish and Danish men, a prolonged interval between ejaculations caused an increase of the sperm count in the semen but not an increase of its amount.
Some dietary supplements have been marketed with claims to increase seminal volume. Like other supplements, including so-called herbal viagra, these are not approved or regulated by the Food and Drug Administration (as licensed medications would be), and none of the claims have been scientifically verified. Similar claims are made about traditional aphrodisiac foods, with an equal lack of verification.
Semen can be stored in diluents such as the Illini Variable Temperature (IVT) diluent, which have been reported to be able to preserve high fertility of semen for over seven days. The IVT diluent is composed of several salts, sugars and antibacterial agents and gassed with CO2.
Semen cryopreservation can be used for far longer storage durations. For human sperm, the longest reported successful storage with this method is 21 years.
In addition to its central role in reproduction, some studies have made claims that semen may have certain beneficial effects on human health:
Other studies claim adversarial effects:
Semen can be the vehicle for many sexually transmitted diseases, including HIV, the virus that causes AIDS.
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.
Semen contains many proteins with potent antimicrobial activity against bacteria, fungi and virus. But none of these proteins are active against Neisseria gonorrhoeae, a common cause of sexually transmitted disease.
The presence of blood in semen or hematospermia may be undetectable (it only can be seen microscopically) or visible in the fluid. Its cause could be the result of inflammation, infection, blockage, or injury of the male reproductive tract or a problem within the urethra, testicles, epididymis or prostate.
It usually clears up without treatment, or with antibiotics, but if persistent further semen analysis and other urogenital system tests might be needed to find out the cause.
In rare cases, people have been known to experience allergic reactions to seminal fluids, known as human seminal plasma hypersensitivity. Symptoms can be either 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.
One 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 of semen allergy can often be overcome by repeated exposure to seminal fluid. In more severe cases, it is important to seek the advice of a physician, particularly in the event that a couple is trying to conceive, in which case, artificial insemination may be indicated.
Scientists at Utrecht University studied the condition whereby some men "get flu-like symptoms such as feverishness, runny nose, extreme fatigue and burning eyes immediately after they ejaculate. Symptoms can last for up to week." This condition is termed post orgasmic illness syndrome or POIS, and it was discovered that this stemmed from an allergy to their own semen, its effects could be cured using hyposensitization therapy or allergen immunotherapy.
A recent study has suggested that semen acts as an antidepressant in women, so that women physically exposed to semen are less likely to suffer from depression. It is thought that the psychological effects of semen are a result of its complex chemical make-up including several mood-altering hormones (testosterone, oestrogen, follicle-stimulating hormone, luteinizing hormone, prolactin and several different prostaglandins). In a scientific survey of 293 college women it was also found that those who did not use condoms were most likely to initiate sex and to seek out new partners as soon as a relationship ended, suggesting that the chemical dependency to semen creates a "rebound effect". The effect of semen on a male sexual partner (as the receiver of semen) is not known.
Qigong and Chinese medicine place huge emphasis on a form of energy called 精 (pinyin: jīng, also a morpheme denoting "essence" or "spirit") – which one attempts to develop and accumulate. "Jing" is sexual energy and is considered to dissipate with ejaculation so masturbation is considered "energy suicide" amongst those who practice this art. According to Qigong theory, energy from many pathways/meridians becomes diverted and transfers itself to the sexual organs during sexual excitement. The ensuing orgasm and ejaculation will then finally expel the energy from the system completely. The Chinese proverb 一滴精，十滴血 (pinyin: yì dī jīng, shí dī xuè, literally: a drop of semen is equal to ten drops of blood) illustrates this point.
The scientific term for semen in Chinese is 精液 (pinyin: jīng yè, literally: fluid of essence/jing) and the term for sperm is 精子 (pinyin: jīng zǐ, literally: basic element of essence/jing), two modern terms with classical referents.
In Ancient Greece, Aristotle remarked on the importance of semen: "For Aristotle, semen is the residue derived from nourishment, that is of blood, that has been highly concocted to the optimum temperature and substance. This can only be emitted by the male as only the male, by nature of his very being, has the requisite heat to concoct blood into semen." According to Aristotle, there is a direct connection between food and semen: "Sperms are the excretion of our food, or to put it more clearly, as the most perfect component of our food."
The connection between food and physical growth, on the one hand, and semen, on the other, allows Aristotle to warn against "engag[ing] in sexual activity at too early an age ... [since] this will affect the growth of their bodies. Nourishment that would otherwise make the body grow is diverted to the production of semen.... Aristotle is saying that at this stage the body is still growing; it is best for sexual activity to begin when its growth is 'no longer abundant', for when the body is more or less at full height, the transformation of nourishment into semen does not drain the body of needed material."
Additionally, "Aristotle tells us that the region round the eyes was the region of the head most fruitful of seed ("most seedy" σπερματικώτατος), pointing to generally recognised effects upon the eyes of sexual indulgence and to practices which imply that seed comes from liquid in the region of the eyes." This may be explained by the belief of the Pythagoreans that "semen is a drop of the brain [τὸ δε σπέρμα εἶναι σταγόνα ἐγκέφαλου]."
Greek Stoic philosophy conceived of the Logos spermatikos ("seminal word") as the principle of active reason that fecundated passive matter. The Jewish philosopher Philo similarly spoke in sexual terms of the Logos as the masculine principle of reason that sowed seeds of virtue in the feminine soul.
The Christian Platonist Clement of Alexandria likened the Logos to physical blood as the "substance of the soul," and noted that some held "that the animal semen is substantially foam of its blood". Clement reflected an early Christian view that "the seed ought not be wasted nor scattered thoughtlessly nor sown in a way it cannot grow."
Women were believed to have their own version, which was stored in the womb and released during climax. Retention was believed to cause female hysteria.
In some pre-industrial societies, semen and other body fluids were revered because they were believed to be magical. Blood is an example of such a fluid, but semen was also widely believed to be of supernatural origin and effect and was, as a result, considered holy or sacred.
Dew was once thought to be a sort of rain that fertilized the earth and, in time, became a metaphor for semen. The Bible employs the term "dew" in this sense in such verses as Song of Solomon 5:2 and Psalm 110:3, declaring, in the latter verse, for example, that the people should follow only a king who was virile enough to be full of the "dew" of youth.
It was widely believed, in ancient times, that gemstones were drops of divine semen which had coagulated after having fertilized the earth. There is an ancient Chinese belief that jade, in particular, was the dried semen of the celestial dragon.
Based upon the resemblance of dandelion juice to human semen, it was historically believed that the flower magically promoted the flow of sperm. (This belief probably derives from the doctrine of signatures.)
The orchid’s twin bulbs were thought to resemble the testicles, and there was an ancient Roman belief that the flower sprang from the spilled semen of copulating satyrs.
Barbara G. Walker recounts these examples of sacred semen in The Woman’s Dictionary of Symbols and Sacred Objects, the thesis of which is that myth and folklore show a pre-patriarchic rule by women that was later supplanted by masculine culture.
In primitive mythology around the world, semen is very often considered analogous to breast milk in some way. In the traditions of Bali, it is considered to be the returning or refunding of the milk of the mother in an alimentary metaphor. The wife feeds her husband who returns to her his semen, the milk of human kindness, as it were.
In some systems of medical philosophy, such as traditional Russian medicine and the Vital Force theory of Herbert Nowell, semen is regarded as the product of a complex physiological interaction between a man and a woman (rather than merely the product of the male reproductive system).
When the British Secret Intelligence Service discovered that semen made a good invisible ink, Sir George Mansfield Smith-Cumming noted of his agents that "Every man (is) his own stylo".
Some reasons for human ingestion of human or other semen are erotic gratification and physical and spiritual benefits.
There is no risk in ingesting the semen of a healthy man. Swallowing semen carries no additional risk other than those inherent in fellatio. Fellatio does carry some transmission risk for sexually transmitted diseases such as HIV or herpes, especially for people with bleeding gums, gingivitis or open sores.
Even if semen is cold before the individual ingests it, viruses can stay active for a long period of time once outside the body.
Research has suggested that performing unprotected oral sex on a person infected with human papillomavirus (HPV) might increase the risk of oral or throat cancer. The study found that 36% of the cancer patients had HPV compared to only 1% of the healthy control group. It is believed that this is due to the transmission of HPV because this virus has been implicated in the majority of cervical cancers.
An average ejaculation (3.4 mL) contains approximately the same amount of protein as the white of an egg. It also has trace amounts of many nutrients such as zinc, calcium and potassium, as well as vitamin B12. The limited studies on the health benefits of semen ingestion are positive.
Some female infertility, preeclampsia and miscarriages are due to the inherent presence of antibodies that destroy the proteins or antigens in her sexual partner's semen. Having oral sex and swallowing the semen of the partner may help make the pregnancy safer and more successful as the woman is ingesting her partner's antigens.
There has been no scientific research conducted into whether oral ingestion of semen has an antidepressive effect, however, semen does contain several mood-elevating compounds such as endorphins, estrone, prolactin, oxytocin, thyrotropin-releasing hormone, and serotonin. The noted beneficial effects of these hormones have thus far been studied with vaginal absorption only.
In some cultures, semen is attributed with special properties of masculinity. Several tribes of Papua New Guinea, including the Sambia and the Etoro, believe that semen provides sexual maturation among the younger men of their tribe. To them, sperm possesses the manly nature of the tribal elders, and in order to pass down their authority and powers, younger men of their next generation must fellate their elders and ingest their semen. This custom commences among prepubescent males and postpubescents. This act may also be attributed to the culturally active homosexuality throughout these and other tribes.
The church father Epiphanius records that the Borborites and other libertine Gnostic sects consumed semen as the Body of Christ. The Pistis Sophia and Testimony of Truth harshly condemn such practices.
In the modern St. Priapus Church, consumption of semen in the presence of others is a form of worship.[dubious ]
There are several sexual practices involving the ingestion of semen. They can be done with one or more partners, like snowballing, felching and creampie eating, or with multiple partners, like the practices of bukkake and gokkun, which originate from Japan.
A huge variety of euphemisms and dysphemisms have been invented to describe semen. For a complete list of terms, see sexual slang.
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