The prostate is a small gland in the male reproductive system whose main job is producing fluid that nourishes, protects, and transports sperm. 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 key to how it works, and also why it can cause problems as men age.
Where the Prostate Sits
Picture a walnut-sized gland tucked directly beneath the bladder. The urethra runs straight through the center of it. This means the prostate essentially acts as a gateway: everything leaving the bladder, whether urine or semen, passes through prostate territory. In a younger man with a healthy prostate, this arrangement works seamlessly. But because the gland tends to grow over time, that shared pathway can become a source of trouble later in life.
In your 40s, the prostate typically weighs around 28 grams. By your 60s it’s closer to 35 grams, and past 75 it can reach 46 grams or more. That growth gradually squeezes the urethra and can slow or interrupt urine flow, which is why urinary symptoms are so common in older men.
Making the Fluid That Carries Sperm
Sperm cells are produced in the testicles, but they can’t survive the journey on their own. The prostate contributes roughly a third of the total fluid in semen, and that fluid is loaded with specific ingredients sperm need. It contains citric acid, which serves as an energy source for sperm cells. It contains zinc, which helps stabilize sperm DNA. And it contains enzymes that keep the fluid at the right consistency.
One of the most important enzymes the prostate produces is PSA (prostate-specific antigen), which most people only associate with cancer screening. Its actual biological purpose is to liquefy semen. Right after ejaculation, semen forms a thick, gel-like clot. PSA breaks that clot down over the next several minutes, freeing sperm cells to swim toward an egg. Without this liquefaction step, sperm would stay trapped in place.
Protecting Sperm From Acid
The vaginal environment is acidic, with a pH designed to ward off bacteria. That acidity is also hostile to sperm. Prostatic fluid solves this problem by being slightly alkaline, with a pH between 7.2 and 7.8. When semen enters the vaginal canal, this alkaline fluid neutralizes enough of the surrounding acid to keep sperm alive and moving. Without that chemical buffer, most sperm would die before reaching the egg.
Pushing Semen Out of the Body
The prostate isn’t just a fluid factory. It’s partly made of smooth muscle, and those muscle fibers play an active role during ejaculation. At the moment of orgasm, the prostate contracts in rhythmic bursts. Each contraction squeezes prostatic fluid into the urethra and helps propel semen forward. Researchers measuring electrical activity in the prostate during ejaculation found that these contractions directly correspond to individual ejaculatory spurts, each one producing a measurable spike in pressure inside the urethra. So the prostate functions as both a chemical contributor and a mechanical pump.
How Hormones Control It
The prostate is heavily regulated by hormones, particularly a potent form of testosterone called DHT (dihydrotestosterone). Your body converts about 10% of its testosterone into DHT each day, and much of that conversion happens in the prostate itself. DHT is what drives the prostate to develop during puberty, and it continues stimulating prostate activity throughout adulthood.
This hormone dependency is a double-edged sword. DHT keeps the prostate functioning normally, but it’s also the main driver behind the gland’s tendency to enlarge with age. That same local DHT production that supports healthy prostate activity also fuels the gradual growth that eventually causes urinary problems in many men. It’s also why some treatments for prostate enlargement work by blocking DHT production.
Why Its Location Causes Urinary Problems
Because the urethra passes directly through the prostate, any increase in prostate size puts pressure on the urinary pathway. This is the root cause of benign prostate enlargement, one of the most common conditions in men over 50. As the gland grows, it can compress the urethra like a clamp around a garden hose. The result is a familiar set of symptoms: a weak urine stream, difficulty starting urination, needing to urinate more frequently (especially at night), and feeling like the bladder hasn’t fully emptied.
These symptoms are not the same as prostate cancer, though they can overlap. Most prostate enlargement is benign, meaning it’s not cancerous. But the symptoms alone can significantly affect quality of life.
Prostate Cancer Screening
PSA, the same enzyme that liquefies semen, also leaks into the bloodstream in small amounts. Elevated blood levels of PSA can signal prostate problems, including cancer. The U.S. Preventive Services Task Force recommends that men between 55 and 69 discuss PSA-based screening with their doctor and make an individual decision based on their own risk factors and preferences. For men 70 and older, the task force recommends against routine PSA screening because the potential harms of overdiagnosis and overtreatment tend to outweigh the benefits at that age.
The most significant risk factors for prostate cancer are older age, African American race, and a family history of the disease. Men with these risk factors may want to start the screening conversation earlier, though no separate formal recommendation exists for these groups. Digital rectal exams, once a standard part of prostate screening, are no longer recommended as a standalone screening tool due to insufficient evidence that they improve outcomes.