The scrotum (SKROH-tum) is a loose, wrinkled pouch beneath the penis, covered with sparse pubic hair. The scrotum contains the testicles, each in a sac, separated by a thin layer of tissue. In the last chapter we discussed how a woman’s gonads (the ovaries) are located in her abdomen. This is different from the male gonads (the testicles), which sit outside the body. This is because the production and survival of sperm require a temperature that is a few degrees lower than the body’s temperature, so the scrotum is actually a kind of cooling tank for the testicles.
When the testicles become too hot, sperm production is halted; in fact, soaking the testicles in hot water has been used as a form of birth control. (Of course, such a technique is highly unreliable, and it takes only a few hardy sperm to undo an hour of uncomfortable soaking. I do not recommend you try it!) Likewise, after a prolonged fever, sperm
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production may be reduced for as long as 2 months. It has also been suggested that men who are trying to impregnate their partner wear loose-fitting underwear, for tight jockstraps or jockey shorts have been shown to reduce sperm counts somewhat, though the effects are reversible (Shafik, 1991). Semen quality has even been shown to undergo seasonal changes, with decreasing quality of semen and sperm counts during the summer (R. J. Levine, 1999).
The scrotum is designed to regulate testicular temperature using two different mechanisms. First, the skin overlying the scrotum contains many sweat glands and sweats freely, which cools the testicles when they become too warm. Second, the cremaster muscle of the scrotum contracts and expands: when the testicles become too cool,
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