Semen
Bodily fluid containing spermatozoa for fertilization.
Semen, also known as seminal fluid, is a bodily fluid that contains spermatozoa from the male gonads of animals. In humans and placental mammals, seminal fluid is ejaculated through the penis via the urethra. This fluid contains proteolytic and other enzymes as well as fructose, which together promote the survival of spermatozoa and provide a medium through which they can move from the vagina into the uterus and to the fallopian tubes, where they can fertilize the female ovum and form a zygote.
- composition
- 70% from seminal vesicles, rest from prostate and bulbourethral glands
- typical volume
- about 3.4 mL (range 2.3–5.0 mL)
- pH range
- 7.2 to 8.0
- sperm concentration
- 20×10^6 spermatozoa/mL or more
- viscosity
- 3–7 centipoises
- appearance
- translucent with white, grey, or yellowish tint
Lore & Background
Semen is collected from animals for artificial insemination or cryoconservation of genetic material. Cryoconservation of animal genetic resources is a practice that calls for the collection of semen in efforts for conservation of a particular breed. 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. Internal fertilization occurs inside the female's sexual organs after a male inseminates a female through copulation.
Reader's Guide
Semen plays a critical role in reproduction across many animal species. In humans, its composition—including fructose, proteolytic enzymes, and basic amines—helps sperm survive the acidic environment of the vagina and reach the fallopian tubes. Semen quality, measured by sperm count, motility, and volume, is a key indicator of male fertility. Semen can also transmit sexually transmitted infections, including HIV and Ebola, and in rare cases cause allergic reactions known as human seminal plasma sensitivity. Beyond reproduction, seminal fluid has been studied for its antiviral and antibacterial properties, and its role in modulating the female reproductive tract's immune environment. Storage methods such as cryopreservation allow semen to be preserved for decades, aiding in genetic conservation and assisted reproduction.
Did You Know?
- Semen contains basic amines such as putrescine, spermine, spermidine, and cadaverine that counteract the acidic environment of the vagina.
- After ejaculation, semen coagulates immediately and then liquefies within 15 to 30 minutes due to prostate-specific antigen.
- The longest reported successful storage of human sperm via cryopreservation is 21 years.
- In macropods, semen coagulates and forms a mating plug in the vagina after copulation.
Frequently Asked Questions
What is Semen?
Semen is a biological fluid produced by the male reproductive system that carries spermatozoa toward the female egg for fertilization. In humans and other placental mammals it is expelled through the urethra during ejaculation.
What role does Semen play in the reproductive storyline?
It acts as the transport and survival medium that carries sperm from the vagina through the uterus and into the fallopian tubes, where fertilization of the ovum can take place. Its enzymatic and nutritional cargo keeps spermatozoa viable throughout that journey.
What is Semen made of?
Roughly 70 percent of the fluid is secreted by the seminal vesicles, with the remaining share contributed by the prostate and bulbourethral glands. The mixture includes fructose, proteolytic enzymes, and other compounds that sustain sperm motility and longevity.
What are Semen's key stats (volume, pH, sperm count)?
A typical sample measures about 3.4 mL (range 2.3–5.0 mL), registers a slightly alkaline pH between 7.2 and 8.0, and carries at least 20 million spermatozoa per milliliter. Viscosity generally falls in the 3–7 centipoise window.
What does Semen look like?
It appears as a translucent fluid with a white, grey, or yellowish tint. The subtle color variation is normal and reflects the blend of secretions from the different contributing glands.
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