The prostate is a small gland in the male reproductive system that produces roughly 25% to 30% of the fluid in semen. It sits just below the bladder and wraps around the urethra, the tube that carries both urine and semen out through the penis. While it’s best known for the problems it can cause as men age, the prostate plays an active role in fertility, urinary control, and sexual function.
Where the Prostate Sits
The prostate is shaped like an inverted cone, about the size of a walnut in younger men. Its wider base surrounds the neck of the bladder, and its narrower tip points downward toward the pelvic floor muscles that help control urination. Behind it sits the rectum, separated by a thin layer of tissue. This is why doctors can feel the prostate during a rectal exam.
The urethra runs directly through the center of the gland. That anatomical quirk is the reason prostate problems so often affect urination: if the gland swells, it squeezes the urethra and restricts flow.
Its Main Job: Producing Seminal Fluid
The prostate’s primary purpose is to contribute a nutrient-rich fluid that mixes with sperm during ejaculation. This prostatic fluid contains zinc, citrate, calcium, magnesium, and potassium, all of which help sperm survive and function properly. The fluid also provides the slightly alkaline environment sperm need to stay viable inside the more acidic female reproductive tract.
One of the key proteins the prostate produces is PSA (prostate-specific antigen). PSA’s actual biological job has nothing to do with cancer screening. It breaks down proteins in freshly ejaculated semen that cause it to clot, allowing the semen to liquefy so sperm can swim freely. Without this step, sperm would remain trapped in a gel-like mass. The zinc and other minerals in prostatic fluid also help synchronize the molecular chain of events that makes sperm motile and capable of fertilization.
How It Affects Urinary Flow
Because the urethra passes through the prostate, the gland’s muscular tissue plays a supporting role in controlling urine flow. During urination, the prostate’s smooth muscle fibers relax to allow urine through. During ejaculation, those same muscles contract to help propel semen forward while preventing urine from mixing in.
This dual role is why an enlarged prostate causes such recognizable urinary symptoms: a weak stream, difficulty starting, frequent urination at night, or the feeling that the bladder hasn’t fully emptied. The muscle tone within the prostate and urethra physically constricts the channel. Medications for this condition often work by relaxing those muscle fibers to open the passage back up.
The Nerves That Run Alongside It
Bundles of nerves responsible for erections run along both sides of the prostate on their way from the pelvic nerve network to the penis. These “cavernous nerves” are the autonomic signals that trigger and maintain an erection. The prostate itself doesn’t control erections, but its location means that any surgery on the gland risks damaging those nerve bundles. This is why nerve-sparing techniques during prostate surgery were such a significant development: preserving those nerves dramatically reduces the chance of erectile dysfunction afterward.
How Hormones Drive Prostate Growth
The prostate is highly sensitive to male hormones, particularly a potent form of testosterone called DHT. An enzyme in prostate tissue converts circulating testosterone into DHT, which stimulates the gland’s normal activity and growth. DHT is also responsible for forming the prostate in the first place during fetal development.
The prostate goes through two major growth phases. The first happens during puberty, when rising testosterone levels cause the gland to reach its adult size. The second begins around age 40 and continues gradually for the rest of a man’s life. Research tracking prostate volume across age groups shows measurable increases decade by decade: average prostate volume rises from about 28 cubic centimeters in men in their 40s to around 35 cubic centimeters by their 60s, a roughly 24% increase over two decades. Length grows the fastest, increasing nearly 10% over that same span.
This ongoing growth is driven by continued DHT activity within the gland. It’s a normal biological process, but in many men it eventually leads to benign prostatic enlargement, which is the most common reason for the urinary symptoms described above. Treatments that block the conversion of testosterone to DHT can slow or reverse this growth.
Why It Causes So Many Problems
The prostate’s location and hormone sensitivity make it uniquely prone to issues as men age. Three conditions account for the vast majority of prostate-related health concerns:
- Benign enlargement is the gradual, non-cancerous growth that affects most men over 50 and causes urinary symptoms by compressing the urethra.
- Prostatitis is inflammation or infection of the gland, which can occur at any age and causes pelvic pain, burning during urination, or flu-like symptoms.
- Prostate cancer is the most common non-skin cancer in men. Because the gland sits deep in the pelvis with critical nerves running along it, treatment decisions often involve weighing cancer control against the risks of urinary and sexual side effects.
All three conditions trace back to the same basic anatomy: a hormone-responsive gland wrapped around the urinary tract, nestled against the rectum, and flanked by the nerves that control erections. The prostate does its reproductive job efficiently, but its design creates trade-offs that become more apparent with age.