Normal Anatomy

About the size of a walnut (20 milliliters), a normal prostate is small and squishy and sits under the bladder and in front of the rectum. The urethra, a narrow tube that runs the length of the penis and carries both urine and semen, runs directly through the prostate. Just below the prostate are the seminal vesicles, which are two little glands that secrete about 60 percent of substances that make up semen. And, running alongside and attached to the sides of the prostate, are the nerves that control erectile function.

Normal Physiology

Though the prostate is not essential for life, it plays a vital role in reproduction. It is believed that the prostate supplies substances that facilitate fertilization and sperm transit and survival. Enzymes like PSA are used to loosen semen and help sperm reach the egg during intercourse (sperm is not made in the prostate, but rather the testes). Substances like zinc, citrate and fructose are made in the seminal vesicles and prostate, which give sperm energy to make the reproductive journey. Substances like antibodies may protect the urinary tract and sperm form bacteria and other pathogens.

The prostate typically grows during adolescence under the control of the male hormone testosterone and its byproduct DHT (dihydrotestosterone).

Treatment-Related Changes

Prostate cancer and its treatments can disrupt normal urinary, bowel and sexual functions, due to its relation to several vital structures.

Urinary function – With normal urinary function, the urinary sphincters remain tightly shut, preventing urine that’s stored in the bladder from leading out (urinary sphincters are the bands of muscle tissue at the base of the bladder and at the base of the prostate). During urination, the sphincters are relaxed and the urine flowers from the bladder through the urethra and out of the body.

During prostatectomy, 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 prostatectomy, or during radiation therapy, some level of urinary incontinence or leakage will occur.

Bowel function – Under normal circumstances, solid waste that’s filtered out of the body moves slowly down the intestines and 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 – During a prostatectomy, erectile nerves may be damaged, resulting in the loss of ability to achieve erection. Despite potential nerve damage, sexual desires are not affected. Nerves can also be damaged by radiation, though the process occurs very slowly over time.

Many techniques in surgery have been developed to try to minimize side effects. These techniques include nerve-sparing surgery, intensity modulated radiation therapy, radiation positioning devices, 3-D conformal radiation technologies and brachytherapy (seed placement).

Fertility – About 10 percent of men with prostate cancer have seminal vesicle invasion, a condition where the cancer spreads into the seminal vesicles or has spread around them. To treat, seminal vesicles are typically removed during prostatectomy and targeted during radiation therapy. This combined treatment of removing both the prostate and seminal vesicles will leave a man infertile and ejaculation is dry. However, orgasms may still occur.