Often described as a walnut or chestnut-shaped organ, the prostate is a gland that surrounds the beginning of the urethra. The prostate produces a milky fluid that provides nutrient to the sperm and is discharged into the urethra at the time of semen emission.

An organ exclusive to men, the development of the prostate is spurred by male hormones (especially testosterone). The rate of prostate growth decreases and may stop around age 20. A second growth period often occurs around age 45, as cells in the middle of the prostate start to reproduce more rapidly than normal. This growth may result in BPH or enlarged prostate.

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.

Normal Anatomy
The normal prostate is a small, squishy gland about the size of a walnut (20 milliliters). 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. The normal prostate is composed of glands and stroma. The glands are seen in cross section to be rounded to irregularly branching. These glands represent the terminal tubular portions of long tubuloalveolar glands that radiate from the urethra. The glands are lined by two cell layers: an outer low cuboidal layer and an inner layer of tall columnar mucin-secreting epithelium. These cells project inward as papillary projections. The fibromuscular stroma between the glands accounts for about half of the volume of the prostate.

As a male ages, there are more likely to be small concretions within the glandular lumina, called corpora amylacea, that represent laminated concretions of prostatic secretions. The glands are normally separated by stroma. The prostate is surrounded by a thin layer of connective tissue that merges with surrounding soft tissues, including nerves. There is no distinct capsule.

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.

Normal Physiology
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.

Prostate Zones
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.

Name	Fraction of gland	Description
Peripheral zone (PZ)	Up to 70% in young men	The sub-capsular portion of the posterior aspect of the prostate gland that surrounds the distal urethra. It is from this portion of the gland that more than 64% of prostatic cancers originate.
Central zone (CZ)	Approximately 25% normally	This zone surrounds the ejaculatory ducts. The central zone accounts for roughly 2.5% of prostate cancers although these cancers tend to be more aggressive and more likely to invade the seminal vesicles.
Transition zone (TZ)	5% at puberty	Prostate cancer originates in this zone in roughly 34% of patients. The transition zone surrounds the proximal urethra and is the region of the prostate gland that grows throughout life and is responsible for the disease of benign prostatic enlargement.
Anterior fibro-muscular zone (or stroma)	Approximately 5%	This zone is usually devoid of glandular components, and composed only, as its name suggests, of muscle and fibrous tissue.

BPH, a non-cancerous prostate condition, typically develops from the transition zone that surrounds the urethra, or urinary tube. This explains why the condition is typically more symptomatic than prostate cancer.

Treatment-Related Changes
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 tissue 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 measure of urinary incontinence or leakage will 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. Sexual desire is not affected, but severing or otherwise damaging the nerves can lead to erectile dysfunction. These nerves can also be damaged by radiation, though this process usually occurs much 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.