The Anatomy and Function of the Prostate Gland

Michelangelo's David notwithstanding, the anatomy of the human male leaves a lot to be desired. Our organs of reproduction and recreation are hopelessly intertwined with our organs of liquid waste disposal. As one observer facetiously noted, ''Only a Civil Engineer could have designed the body [since] who else would design a waste disposal line through a recreational area?''1

Sitting in the center of this anatomical assemblage is the prostate, a reddish-brown organ approximately an inch and a half in diameter. It lies at the bottom of the pelvis, with the penis below, the bladder above, the pelvic bone in front, and the rectum behind (Figure 3). This last juxtaposition is especially important, because feeling the prostate through the rectal wall—the much-maligned digital rectal exam—is the only way a physician can physically assess this organ. Fortunately, the majority of cancers develop in the posterior portion of the prostate, thereby making them detectable to a skilled examining finger.

The prostate has been variously described as looking like a walnut, a chestnut, or a small plum. In a young man, it weighs approximately 20 gm, then increases in size as the man ages. It contains muscles and glands, the latter secreting fluid that assists and protects male sperm. One component of the prostate fluid is prostate specific antigen (PSA), described in Chapter 2.

f^ure3. ioratton of Prostate

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The prostate contributes approximately one third of the fluid that makes up the semen. The other two thirds comes from the paired seminal vesicles, small glands that sit at the base of the bladder and drain through the prostate into the urethra. Joining the seminal vesicle ducts in the prostate are the paired vasa deferentia, which carry sperm from the testicles. The vasa deferentia, seminal vesicle ducts, and ducts from the internal prostate glands all join together at the urethra in the middle of the prostate (Figure 4).

Thus, the prostate center is the Grand Central Station of the male reproductive system. There, at the time of orgasm, sperm and the accompanying fluid begin their journey down the urethra, through the penis, and with luck up the vagina and uterus, perhaps to find a waiting egg in the fallopian tubes. According to Dr. Peter Scardino's Prostate Book, the sperm travel ''at the startling rate of 28 miles per hour, which, by amusing coincidence, is also the top speed a world-class human runner can achieve during a sprint.''2

This complicated system would work fine, except for the fact that the urethra has a second function, as the exit for urine. Filtered by the kidneys and then deposited into the bladder, which sits on top

Where The Prostate Gland Sitting Down

What a Curious Organ

I would like to sit down with my doctor and talk to him about the prostate. What a curious organ. What can God have been thinking when He designed it this way?

—Anatole Broyard, Intoxicated by My Illness

of the prostate, urine passes via the urethra directly through the middle of the prostate. To avoid a constant dribble of urine, the muscles at the base of the bladder function as an internal sphincter (although technically they are not a true sphincter). The urethra also has an external sphincter, a true sphincter, just below the prostate. Both sphincters must relax for urination to take place.

When one or both sphincters are damaged, as during surgical

removal of the prostate, or are not working properly, which may happen as a side effect of medication, the result may be some degree of incontinence. During orgasm and ejaculation, the external sphincter opens to allow the semen to leave, while the internal sphincter closes to prevent semen from flowing upward into the bladder. When the sphincters do not work properly, semen may flow into the bladder; this is called retrograde ejaculation. It is harmless, but obviously does not result in the fertilization of female eggs. Alternatively, if the internal sphincter does not close during orgasm, urine may descend through the urethra, a common but usually temporary complication of surgical removal of the prostate (see Chapter 3).

But this anatomical anarchy actually is even worse. Running close to the sides of the prostate are tiny arteries, veins, and nerves that go to the penis and control erection. If they are damaged during surgical removal or irradiation of the prostate, the man may achieve only a partial erection or no erection at all. This impotence is a common side effect of prostate cancer treatment, as discussed in Chapter 10.

Given this anatomy, it becomes apparent why enlargement of the prostate, due to either benign prostatic hypertrophy (BPH) or cancer, may cause serious problems. An enlargement of the prostate may squeeze the urethra, thereby making the urinary stream progressively smaller and urination more difficult. This process occurs commonly in aging men, since the prostate begins to enlarge during middle age. The reason for this enlargement is unknown; it is caused by testosterone stimulation but appears to serve no useful evolu tionary purpose other than to make urology a necessary medical specialty.

Given this anatomy, it also becomes apparent why treating prostate cancer can so often lead to incontinence and impotence. It is virtually impossible to surgically excise, irradiate, or otherwise remove a cancerous growth in the prostate without damaging surrounding structures. As one observer summarized the situation: ''God's specialty was humanity, not urology.''3

Most people assume that prostate cancer is a disease exclusively of men. This is not quite true. In the first few weeks of development in utero, males and females are exactly alike. The anatomy of both develops from the same structures. Therefore, there are remnants of female structures in males, and remnants of male structures in females. In women, the remnants of the prostate are tiny, paired para-urethral glands that lie beside the urethra. Rarely, these glands can become cancerous, the result being a female equivalent of prostate cancer. Approximately sixty such cases have been described in the medical literature. Thus, we have equality between the sexes: men can (rarely) get breast cancer, and women can (rarely) get the equivalent of prostate cancer.

APPENDIX B

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