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The more you know about the normal development and function of the prostate, where it’s located, and what it’s attached to, the better you can understand how prostate cancer develops and impacts a man’s life over time—due either to cancer growth or as a result of treatments.
The normal prostate is a small, squishy gland about the size of a walnut. It sits under the bladder and in front of the rectum. The urethra—the narrow tube that runs the length of the penis and carries both urine and semen out of the body—runs directly through the prostate. The rectum, or lower end of the bowel, sits just behind the prostate and the bladder.
Sitting just above the prostate are the seminal vesicles—two little glands that secrete about 60% of the substances that make up semen. Running alongside and attached to the sides of the prostate are the nerves that control erectile function.
The prostate is not essential for life, but it’s important for reproduction. It seems to supply substances that facilitate fertilization and sperm transit and survival. Enzymes like PSA are actually used to loosen up semen to help sperm reach the egg during intercourse. (Sperm is not made in the prostate, but rather the testes.)
Other substances made by the seminal vesicles and prostate—such as zinc, citrate, and fructose—give sperm energy to make this journey. Substances like antibodies may protect the urinary tract and sperm from bacteria and other pathogens.
The prostate typically grows during adolescence under the control of the male hormone testosterone and its byproduct DHT, or dihydrotestosterone.
The prostate is divided into several anatomic regions, or zones. Most prostate cancer develops from the peripheral zone near the rectum. That’s why a digital rectal exam (DRE) is a useful screening test.
Benign prostatic hypertrophy (BPH), a non-cancerous prostate condition, typically develops from the transition zone that surrounds the urethra, or urinary tube. This is why BPH causes more difficulty with urination than prostate cancer typically does.
Because the prostate is close to several vital structures, prostate cancer and its treatment strategies can disrupt normal urinary, bowel, and sexual functioning.
Urinary function—Under normal circumstances, the urinary sphincters (bands of muscle at the base of the bladder and at the base of the prostate) remain tightly shut, preventing urine that’s stored in the bladder from leaking out. During urination, the sphincters are relaxed and the urine flows from the bladder through the urethra and out of the body.
During prostatectomy—the surgical removal of the prostate—the bladder is pulled downward and connected to the urethra at the point where the prostate once sat. If the sphincter at the base of the bladder is damaged during this process, or if it’s damaged during radiation therapy, some degree of urinary incontinence or leakage may occur.
Bowel function—Solid waste that’s filtered out of the body moves slowly down the intestines, and, under normal circumstances, the resultant stool is excreted through the anus following conscious relaxation of the anal sphincter. Damage to the rectum caused by radiation, or more rarely, by surgery, can result in bowel problems, including rectal bleeding, diarrhea, or urgency.
Sexual function—If the erectile nerves are damaged during prostatectomy, which was standard during this type of surgery up until the mid-1980s, the ability to achieve erection is lost, though sexual desire is not affected. Erectile dysfunction can also result from damage to these nerves by radiation therapy, though this process usually occurs more slowly over time.
Modern techniques in surgery (nerve-sparing), radiation (intensity modulated radiation therapy, positioning devices, 3-D conformal technologies), and seed placement (brachytherapy) have been developed to try to minimize these side effects, and this process continues to improve.
Fertility—About 10% of men with prostate cancer have what is known as seminal vesicle invasion. This means the cancer has either spread into the seminal vesicles or has spread around them. If that occurs, seminal vesicles are typically removed during prostatectomy and targeted during radiation therapy. The loss of the prostate and the seminal vesicles renders men infertile. After surgical removal, ejaculation is dry, but orgasms may still occur.