Click on the diagram to the left (on any numbered region on the left hand side) to cause this window to scroll...
You will learn the roll of each of these regions in the production of semen.
The testis produces the spermatozoa for the semen. However, at the time the spermatozoa leave the testis, they still are not mature. They can only swim in a poorly-coordinated fashion, and they are not yet fully capable of fertilization. You will see that other fluids that contribute to the semen help to fully activate the spermatozoa. The spermatozoa move out of the testis and into the epididymus continually.
The epididymus is like a storage area for the spermatozoa. After the spermatozoa are born, they make their way into the epididymus, where they await their release. Within the epididymus, the sperm are found in ducts. The cells lining the ducts secrete glycogen (the polysaccharide) and other substances. These substances nourish and support the spermatozoa, helping them to mature. The maturation of the sperm into cells capable of coordinated movement occurs here.
The spermatozoa leave the epididymus during ejaculation (in a little bit of fluid). As they travel through the male reproductive system, other secretions are added to the spermatozoa-containing solution.
3. Vas deferens
Also called the "ductus deferens," this region is strictly for transport of spermatozoa.
This is just a widened area of the vas deferens. It has no additional function for the production of semen. It is just that your book points it out so much that I thought I should indicate it and tell you of its little significance.
5. Seminal vesicle
The seminal vesicles secrete a fluid that contains:
fructose: a monosaccharide that spermatozoa can use to produce ATP... swimming is hard work and is quite energetically costly for the spermatozoa!
prostaglandins: a kind of hormone that causes the female reproductive organs to undergo smooth muscle contractions. You see, when the spermatozoa enter the female reproductive system, they have a long way to go before they reach the egg (if it is there!). The smooth muscle contractions are peristaltic contractions that help move the spermatozoa toward the ovaries.
a basic solution: the spermatozoa may have been stored for quite some time... in that case, they tend to accumulate cellular metabolism wastes, making their solution more acidic. The basic (alkaline) solution brings the pH of the spermatozoa-solution back toward a more neutral pH. Meanwhile, the female reproductive tract is a bit acidic, so the basic pH of the seminal vesicle secretion also helps to counteract that condition; the seminal fluid is only a little basic, though.
The seminal vesicle secretion is released during ejaculation and comprises a portion of the semen.
6. Prostate gland
The prostate gland also adds fluid to the semen. This fluid is milky in appearance. It is a basic solution, and serves the same role as the basic solution of the seminal vesicle. However, the prostate gland secretion is a bit more basic than the seminal vesicle secretion. So it is even more effective at restoring a more neutral semen pH and counteracting the acidic environment of the female reproductive system.
The prostate gland secretion also has the effect of increasing spermatozoan motility.
The prostate gland only secretes its fluid during ejaculation.
Note that when the prostate gland is removed, as is done during surgery for prostate cancer, the basic, milky secretion can no longer be added to the semen. Semen is still emitted during ejaculation, but the semen will not be effective for fertilization since the spermatozoa will not be as motile and the semen will be too acidic.
7. Bulbourethral gland
The bulbourethral glands (a.k.a., Cowper's glands) secrete a mucus-like fluid that is not really a semen component. Instead, the bulbourethral glands secrete during sexual arousal, not just during ejaculation, and serve to lubricate the end of the penis. Therefore the role of these glands is in facilitating internal fertilization, not in contributing to semen.
In addition, because the secretions of the bulbourethral glands occur before intercourse, it is thought that a secondary function of these secretions is to clear the urethra of any urine/wastes that may still be within it before the semen passes through.