Semen

As we have seen, the semen or seminal fluid ejaculated through the opening of the penis comes from a variety of sources. Fluids are supplied by the seminal vesicles, the prostate gland, and the Cowper’s glands, with the seminal vesicles providing the greatest portion (DeMoranville, 2008). The amount of seminal fluid that a man ejaculates—roughly 1 teaspoon on average—is influenced by a number of factors, including the length of time since the last ejaculation, the duration of arousal before ejaculation, and age (older men tend to produce less fluid). The semen of a single ejaculation typically contains between 200 million and 500 million sperm, which account for only about 1% of the fluid’s total volume. Chemical analysis shows that semen is also made up of ascorbic and citric acids, water, enzymes, fructose, bases (phosphate and bicarbonate buffers), and a variety of other substances. None of these materials is harmful if swallowed during oral sex. How­ever, semen of an HIV-infected man can transmit the virus to the man’s partner if the recipient has open sores or bleeding gums in his or her mouth (see Chapter 15).