Semen

Semen, also known as seminal fluid, is an organic fluid created to contain spermatozoa. It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals and can fertilize the female ovum. In humans, seminal fluid contains several components besides spermatozoa: proteolytic and other enzymes, as well as fructose, are elements of seminal fluid that 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. Semen is also a form of genetic material. In animals, semen has been collected for cryo conservation. Cryoconservation of animal genetic resources is a practice that calls for the collection of genetic material in efforts for the conservation of a particular breed.

Fertilization

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 the insemination of a female by a male through copulation. In most vertebrates, including 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.

Human semen

Composition

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 ductal fluid by reabsorbing some fluid. Once the semen enters the ductus epididymis the principal 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 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 (c.f. sexual conflict) 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 flavour 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: (SOURCE: wikipedia)

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 20×106 spermatozoa/mL or more, sperm count of 40×106 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:

Appearance and consistency

Human semen in a petri dish

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 that 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 to 30 minutes, a prostate-specific antigen present in the semen causes the de coagulation 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.

Quality

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.

Quantity

The volume of semen ejaculate varies but is generally about 1 teaspoonful or less. A review of 30 studies concluded that the average was around 3.4 millilitres (mL), with some studies finding amounts as high as 5.0 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 in its amount.

Increasing semen volume

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 in the US would be), and none of the claims has been scientifically verified. Similar claims are made about traditional aphrodisiac foods, with an equal lack of verification.

Storage Semen can be stored in diluents such as the Illini Variable Temperature (IVT) diluent, which have been reported to be able to preserve the 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.

Health

Disease transmission

Semen can transmit many sexually transmitted diseases and pathogens, including viruses like HIV and Ebola. Swallowing semen carries no additional risk other than those inherent in fellatio. This includes transmission risk for sexually transmitted diseases such as human papillomavirus (HPV) or herpes, especially for people with bleeding gums, gingivitis or open sores. Viruses in semen survive for a long time once outside the body.[medical citation needed] Blood in semen (hematospermia)

The presence of blood in semen or hematospermia may be undetectable (it can only 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.

Semen allergy

In rare circumstances, humans can develop an allergy to semen, called human seminal plasma sensitivity. It appears as a typical localized or systemic allergic response upon contact with seminal fluid. There is no one protein in semen responsible for the reaction. Symptoms can appear after first intercourse or after subsequent intercourse. A semen allergy can be distinguished from a latex allergy by determining if the symptoms disappear with the use of a condom. Desensitization treatments are often very successful.

Benefits to females

Females may benefit from absorbing seminal fluid. Such benefits include male insects transferring nutrients to females via their ejaculate; in both humans and bovines, the fluid has antiviral and antibacterial properties; and useful bacteria such as Lactobacillus have been detected in fluid transferred from birds and mammals.