The prostate is a small gland that produces most of the fluid in semen, helping sperm survive and reach an egg. About the size of a walnut and weighing roughly 30 grams (the weight of five quarters), it sits just below the bladder and wraps around the urethra, the tube that carries both urine and semen out of the body. That positioning is central to how the prostate does its job, and also explains why prostate problems so often affect urination.
Where the Prostate Sits and Why It Matters
The prostate is tucked between the bladder above and the rectum behind it. The urethra runs directly through the center of the gland, which means any change in prostate size can squeeze the urethra and restrict urine flow. This is why enlarged prostates cause urinary symptoms like weak streams, frequent nighttime trips to the bathroom, and difficulty fully emptying the bladder.
The gland’s location in front of the rectum is also why doctors can feel it during a digital rectal exam. The back wall of the prostate sits close enough to the rectal wall that a physician can assess its size, shape, and firmness through a simple physical check.
What the Prostate Actually Produces
The prostate’s primary job is manufacturing a thin, slightly alkaline fluid that makes up roughly 20 to 30 percent of semen volume. This fluid isn’t just a carrier for sperm. It contains a specific mix of components that keep sperm alive and functional long enough to fertilize an egg.
Citric acid is one of the most concentrated ingredients, providing energy that sperm cells use as fuel. Zinc, present in smaller amounts, acts as a natural antibacterial agent, protecting both the prostate itself and the broader urinary and reproductive tract from infection. The fluid also contains specialized enzymes that break down proteins. These enzymes serve a specific purpose: they liquefy semen after ejaculation and help sperm push through cervical mucus and the protective outer layer of the egg.
Perhaps the most important function of prostatic fluid is neutralizing acidity. The vaginal environment is naturally acidic, which would kill most sperm within minutes. The alkaline prostatic fluid buffers that acidity, giving sperm a much longer window to reach the egg. Without this protection, fertility would drop dramatically.
The prostate also produces PSA (prostate-specific antigen), a protein that helps keep semen liquid. PSA is the same substance measured in blood tests used to screen for prostate problems, since small amounts leak into the bloodstream.
How the Prostate Works During Ejaculation
The prostate isn’t just a passive factory. It contains smooth muscle tissue that actively contracts during ejaculation to push its fluid into the urethra at precisely the right moment. Electrophysiology studies show that the prostate generates slow electrical waves even at rest, producing mild contractions that gently squeeze secretions into the urethra. During ejaculation, these electrical signals ramp up significantly, and the contractions become much stronger and more rhythmic.
Each contraction coincides with an ejaculatory spurt. The prostate’s muscle contractions also help increase pressure within the prostatic section of the urethra, which works alongside the bladder neck closing off to ensure semen travels outward rather than backward into the bladder. This coordination between the prostate, the bladder neck, and the pelvic floor muscles happens automatically through nerve signals, all within a few seconds.
How Hormones Control Prostate Growth
The prostate depends on male hormones (androgens) to develop, function, and maintain its tissue. Testosterone, produced mostly in the testes, is the starting material. But inside prostate cells, an enzyme converts testosterone into a much more potent form called DHT. This converted hormone is the primary driver of prostate activity.
DHT binds to receptors inside prostate cells and switches on genes that regulate cell growth and secretion. During fetal development and puberty, DHT is essential for building the prostate and developing male reproductive anatomy. In a healthy adult prostate, DHT maintains a careful balance between new cell growth and natural cell death, keeping the gland at a stable size.
The problem is that this system doesn’t always stay balanced as men age. DHT can tip the scales toward too much cell growth and too little cell death, causing the prostate to enlarge gradually over decades. This is the hormonal mechanism behind benign prostatic hyperplasia, or BPH, the most common prostate condition in older men.
How the Prostate Changes With Age
A healthy prostate in a man’s 20s or 30s weighs about 28 to 30 grams. By the 40s, the gland typically starts growing. Average weight climbs to about 31 grams by the 50s, 35 grams by the 60s, and over 46 grams past age 75. In some men, the prostate can eventually reach the size of a lemon.
This growth isn’t always a problem. Many men with enlarged prostates have no symptoms at all. But for a significant number, the expanding tissue presses on the urethra and causes noticeable urinary changes. Among men aged 40 to 64, about 5 to 6 percent have been diagnosed with BPH and related lower urinary tract symptoms. That number jumps to 29 to 35 percent for men 65 and older. Autopsy studies paint an even broader picture: 90 percent of men over 80 show microscopic evidence of BPH, whether or not they ever experienced symptoms.
Medications that block the enzyme converting testosterone to DHT can slow or reverse this growth by shrinking the prostate, improving urine flow, and reducing the risk of complications like complete urinary blockage. These are the only treatments that target the underlying hormonal cause of the enlargement rather than just managing symptoms.
PSA and What It Tells You
Because the prostate produces PSA and releases small amounts into the bloodstream, a blood test can measure PSA levels as a general indicator of prostate health. There is no single “normal” number. PSA levels naturally rise with age and with prostate size, so a reading that’s unremarkable for a 70-year-old might warrant further investigation in a 45-year-old.
As a general guideline, levels above 4.0 ng/mL are often flagged for follow-up. Some doctors use lower thresholds (around 2.5 ng/mL) for younger men and higher ones (around 5.0 ng/mL) for older men. An elevated PSA doesn’t mean cancer is present. Infections, recent ejaculation, BPH, and even vigorous exercise can temporarily raise PSA. The test is a screening tool, not a diagnosis.