Sex For Dummies. Dr. Ruth K. Westheimer
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Название: Sex For Dummies
Автор: Dr. Ruth K. Westheimer
Издательство: John Wiley & Sons Limited
Жанр: Секс и семейная психология
isbn: 9781119596585
isbn:
For the sperm to be successful at their task of making babies, they have to overcome many obstacles after making a long journey. You may well recognize their final shape — an oval head with a long tail that helps to propel them along — but sperm don’t start out that way (see Figure 2-4).
Illustration by Kathryn Born
FIGURE 2-4: The sperm: independent, a good swimmer, and a heckuva guy.
From humble beginnings
Early in their life cycles, sperm are called germ cells. (In this case, I think most people would have preferred a nice, long Latin name; but rest assured, these cells have nothing to do with what we commonly associate the word germ.)
Germ cells are produced in the seminiferous tubules, which are long, spaghetti-like tubes that are connected to each other, packed into a tight ball, and surrounded by a tough membrane. This package is called — drumroll, please — a testicle. (Between these tubes are cells that produce the male hormone testosterone.) As the germ cells travel along the tubes, slowly but surely they turn into sperm.
Their metamorphosis complete, the sperm leave the testicle and head for the epididymis on their way to the vas deferens. (Now’s the time to look at Figure 2-5, and be amazed that sperm can find their way without any help from GPS.)
Illustration by Kathryn Born
FIGURE 2-5: The sperm leave the testicle and head for the epididymis and vas deferens.
Meiosis: Small division
Now that you’ve had a chance to look at the diagram and can picture in your mind’s eye the journey that the spermatozoa take, I have to tell you about one more important transformation that they make.
When a germ cell undergoes meiosis, it forms two new cells, each of them having only half of the DNA code: 23 bits of genetic material (called chromosomes) instead of the normal 46.
When a sperm teams up with a female egg, which also only has 23 chromosomes, their genetic materials intertwine, and the resulting baby ends up with a package containing a total of 46 chromosomes that is a mixture of both the mother’s and the father’s genetic material.
When the male germ cells divide, the sex chromosomes divide also. The male has one X and one Y chromosome; the female has two X chromosomes.
Whether the sperm that reaches the egg first has an X (female) or Y (male) chromosome determines whether the baby will be a girl or a boy.
When they’re ready, the sperm leave the testes (another name for testicles) and enter the epididymis, which is a series of tiny tubes that lie on top of the testes. (For those of you into amazing statistics: If unfurled, these tubes would reach 60 feet in length.) During their journey through the epididymis, sperm learn to swim. They enter the epididymis with useless tails and leave it as little speed demons. (See the advice that practice makes perfect lies at the very heart of human life.)
Vas deferens
If you go back to Figure 2-5, you see that the sperm’s next stop on their voyage is the vas deferens, a tube that ejects the sperm into the urethra, through which semen and urine pass. In the urethra, the sperm are mixed with fluids from the seminal vesicles and the prostate (which I discuss in more detail later in the “The Prostate Gland” section); then they make their way out into the world through ejaculation.
The combination of these fluids and the sperm is called semen. The amount of semen ejaculated during orgasm is generally around a teaspoonful, though it varies depending on when the man last ejaculated. The semen is whitish in color, has a distinctive smell, and is thick when it first comes out. Sperm only comprise about 5 to 10 percent of the volume, but they are the only part of the semen that can cause pregnancy.
Too few sperm (male infertility)
Just because your testicles look normal doesn’t mean that they are fully functioning. If a couple tries to conceive but can’t seem to do it, one of the first things that doctors look for is a problem with the man’s sperm. The most common problems are a low sperm count (which means that the man isn’t producing enough sperm) or the sperm he is producing lack sufficient motility, the ability to swim to the egg. The basis for the problems may be abnormal sperm production, which can be difficult to treat or can be as simple as changing from tighty whities to boxers because heat is known to decrease sperm count. Another cause can be a blockage somewhere along the line, which may be corrected through surgery.
Interestingly enough, most semen analysis is done by gynecologists, specialists in the female reproductive system. A gynecologist is usually the first person a woman consults when she has problems getting pregnant. Commonly, the gynecologist asks that the man’s sperm be analyzed. If the tests reveal a problem with the sperm, the man is sent to a urologist for further evaluation.
Why boys wear cups
Despite the fact that some men adopt a tough-guy, macho image, the heart of their maleness, the testicles, is highly sensitive. The testicles are so sensitive that men may experience some pain down there just by thinking about the pain that occurs when their testicles are struck by an object.
If a boy has never had the sensations caused by a blow to the scrotum, then he may not see the need to wear СКАЧАТЬ