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Facts about sex:  What is semen?

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Semen is the scientific name for the fluid a man ejaculates at the point of orgasm. It is made up of sperm, which are produced in the testicles, and seminal fluid, which is produced by the various sex glands. Seminal fluid is a highly complex fluid with many different components. 

The most important sex glands involved in production of the seminal fluid are the seminal vesicles at the base of the bladder. They secrete a viscous alkaline fluid which makes up about 60% of the volume of semen.  The alkaline quality of semen is very important as it neutralizes the acidic environment of the male urethra and the female vagina, which would kill sperm or make it inactive. The fluid from the seminal vesicles also contains fructose, a simple sugar molecule, which provides energy for the sperm to survive and move about. Both the excretions from the seminal vesicles and a much smaller contribution from the Cowper's glands give semen its sticky quality.

The second main source of seminal fluid is the prostate gland. Its secretions make up about 25% of the volume of semen and give it its milky appearance. The prostate adds substances  which increase the sperms' survival rate and their ability to move about. 

The average amount of fluid a man ejaculates is between 2.5 and 5 ml with an average sperm count of 50 - 150 million sperm per milliliter. If the sperm count falls below 20 million per milliliter a man is likely to be infertile. The amount of ejaculate varies greatly with how long a man's sexual arousal lasts for before he ejaculates. Once a man becomes aroused more fluids are produced by the glands. So if you take longer over your foreplay, your glands have more time to produce a greater volume of fluid, which may not necessarily impress your female partner, but will increase the strength and pleasure of your orgasmic and ejaculatory contractions.

Semen tends to be sticky and thick right after ejaculation, but soon liquefies somewhat and becomes more runny. This is a normal process that occurs in all men. It is also normal for the color and texture of semen to vary over time, ranging from a homogenous milky fluid to a clear liquid with streaks of milky fluid in it, and even gelatinous globules.


Occasionally men my experience other colorations of their semen, such as a pink color. The pink color is due to blood in the semen, but this can be a minor thing or it could be the sign of something more important:

1) It could be due to minor trauma, for example, you may have been quite strong in stimulating yourself recently or during sex with a partner. In this case there would be nothing else to worry about and the pink color should not continue. The blood in the semen would be due to a burst blood vessel, similar to a burst blood vessel in the white of a person's eye.

2) You may have had unprotected intercourse recently and the pink may be the sign of a sexual infection (STD) you may have caught. If this is a possibility you need to go to a medical doctor to get yourself screened.

3) Should the pink color continue please do go to a medical doctor to get yourself checked. It is important that you look after your health even if this may be expensive! The pink color could be a sign of a general problem and needs investigating.


Source for the facts cited in this page: 

ABC of Sexual Health (2005) Second edition edited by John M Tomlinson, British Medical Journal Books and Blackwell Publishing.

Principles of anatomy and physiology (2000) Ninth edition by Gerard J. Tortora and Sandra Reynolds Grabowski. Publishers: John Wiley and Sons

Written by Anna, 12.01.07


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