The prostate gland produces a nutrient-rich fluid that makes up roughly 20 to 30 percent of semen, helping keep sperm alive and functional after ejaculation. But fluid production is only one of its jobs. The prostate also plays an active role in ejaculation itself and acts as a valve that separates the urinary and reproductive systems.
What the Prostate Produces and Why
The prostate secretes a thin, slightly alkaline fluid loaded with enzymes, zinc, citric acid (citrate), calcium, and magnesium, all in concentrations far higher than anywhere else in the body. Each of these components serves a purpose. Zinc has antibacterial properties that help protect the reproductive tract from infection. Citrate provides an energy source that sperm cells burn as fuel. The enzymes help liquefy semen after ejaculation so sperm can swim freely.
The fluid’s chemistry also controls the pH of semen. The vaginal canal is naturally acidic, which is hostile to sperm. Prostatic fluid buffers that acidity, creating a more survivable environment. Within the prostatic fluid itself, pH can range from about 6.2 to 8.0 depending on citrate levels, but the overall effect on semen is protective.
Its Role During Ejaculation
The prostate isn’t just a passive gland that drips fluid into the mix. It contains smooth muscle tissue that contracts rhythmically during ejaculation, squeezing its secretions into the urethra at precisely timed intervals. Electrophysiology studies have recorded these contractions occurring in bursts roughly one second apart, with an average of about four to five spurts per ejaculation. Each contraction coincides with a measurable spike in pressure inside the prostatic urethra, which helps propel semen outward. Without this muscular action, ejaculation would lack the force needed to expel semen effectively.
A Valve Between Two Systems
The prostate sits just below the bladder, wrapped around the urethra, the tube that carries both urine and semen out of the body. This positioning lets it function as a traffic controller. Muscles around the prostate form an involuntary valve where the bladder meets the urethra. During urination, these muscles relax to let urine flow. During sexual activity, they close off the bladder so semen travels outward instead of backward. You can’t consciously control this valve; it operates automatically.
How Hormones Drive the Prostate
The prostate depends on male sex hormones, particularly a potent form of testosterone called DHT. The prostate itself converts testosterone into DHT locally, and this locally produced DHT is what stimulates the gland to grow during puberty and maintain its secretory activity throughout adulthood. DHT is responsible for keeping prostate cells active and productive. It’s also, unfortunately, the main driver behind the gland’s tendency to keep growing with age, which leads to common problems later in life.
Size, Location, and Structure
A healthy adult prostate weighs about 25 grams and is roughly the size of a walnut. It sits below the bladder and in front of the rectum, which is why doctors can feel it during a rectal exam. The urethra runs directly through its center, a detail that becomes medically significant if the gland enlarges. The prostate is divided into several zones, with the inner transition zone being the area most prone to growth and the outer peripheral zone being where most cancers develop.
How the Prostate Changes With Age
In your 20s, the prostate is walnut-sized and typically causes no issues. By 40, it may have grown slightly. By 60, it’s often the size of a lemon, and in some men it can exceed three times its normal weight, surpassing 80 grams. This age-related growth is called benign prostatic hyperplasia (BPH), and it’s extremely common.
BPH doesn’t mean cancer. It’s a noncancerous overgrowth of prostate tissue driven by decades of DHT exposure. The problem is mechanical: as the prostate swells, it squeezes the urethra running through it and presses against the bladder. This gradually interferes with the very urinary function the prostate is supposed to support.
The symptoms are recognizable. You may need to urinate more often, especially at night. Starting a stream may require straining. The flow itself can feel weak, slow, or stop-and-start. You might feel like your bladder never fully empties, or experience sudden urgent needs to urinate. In more advanced cases, BPH can cause painful urination, pain after ejaculation, or blood in the urine.
None of these symptoms mean the prostate has stopped performing its reproductive functions. It still produces fluid and still contracts during ejaculation. But the growth that causes BPH can make the urinary valve function progressively worse, turning what was once an efficient two-system switch into a bottleneck.