The prostate gland produces a nutrient-rich fluid that makes up roughly 25% to 30% of semen. This fluid nourishes and protects sperm, helping them survive long enough to reach and fertilize an egg. But the prostate does more than just produce fluid. It also acts as a muscular pump during ejaculation and plays a gatekeeping role between the urinary and reproductive systems.
Where the Prostate Sits and Why That Matters
The prostate is a small, walnut-sized gland that wraps around the urethra, the tube that carries both urine and semen out of the body. It sits just below the bladder. This positioning is central to its function: the urethra passes directly through the prostate, giving the gland a dual role in both urination and reproduction. In younger men, the prostate typically has a volume of about 28 cubic centimeters. By age 60 to 70, that average rises to around 35 cubic centimeters, a slow growth of roughly 2% to 2.5% per year.
Producing the Fluid That Keeps Sperm Alive
Sperm cells are made in the testicles, but they can’t survive the journey to an egg on their own. The prostatic fluid they travel in contains zinc, citrate, calcium, magnesium, and potassium, all of which support sperm health in specific ways.
Zinc is one of the most important components. The prostate concentrates zinc at levels far higher than any other tissue in the body. This zinc stabilizes the tightly packed DNA inside each sperm cell by forming structural bonds that hold the genetic material together. It also protects sperm membranes from oxidative damage and has antibacterial properties. Fertile men have significantly higher zinc concentrations in their semen than infertile men, roughly 14 mg per 100 ml compared to about 10 mg per 100 ml.
The fluid also helps buffer acidity. The vaginal environment is naturally acidic, which would kill unprotected sperm within minutes. Prostatic secretions have a pH between 6.5 and 7.2, and the proteins and phosphates in semen create a buffering system that keeps the overall pH in the range of 7.0 to 8.5, the zone where sperm can migrate and survive in cervical mucus.
Liquefying Semen So Sperm Can Move
Immediately after ejaculation, semen forms a thick, gel-like clot. This coagulation is caused by proteins from the seminal vesicles (another set of glands). If semen stayed in this clotted state, sperm would be trapped and unable to swim.
The prostate solves this by producing an enzyme called prostate-specific antigen, or PSA. Most people know PSA as a blood test marker for prostate problems, but its actual biological job is to break down those clotting proteins. PSA acts like a molecular scissors, cutting the gel into a thinner liquid over the course of several minutes. This liquefaction frees the sperm cells to begin swimming toward the egg. Without this process, fertility would be severely compromised.
The Muscular Pump Behind Ejaculation
The prostate isn’t just a gland. It’s also packed with smooth muscle fibers, both inside its tissue and in the connective tissue capsule that surrounds it. During ejaculation, these muscle cells contract forcefully, squeezing stored prostatic fluid out into the urethra. This happens in coordination with the release of sperm from the testicles and fluid from the seminal vesicles, combining everything into semen at the moment of ejaculation. The prostate’s contractions are part of what gives ejaculation its pulsing, forceful quality.
How Hormones Control the Prostate
The prostate is one of the most hormone-sensitive organs in the male body. Testosterone circulating in the blood reaches the prostate, where an enzyme converts it into a more potent form called DHT (dihydrotestosterone). DHT is the primary driver of prostate growth and function throughout life. During fetal development, DHT is responsible for forming the prostate in the first place. During puberty, it triggers the prostate to grow to its adult size and begin producing fluid. In adulthood, DHT maintains the gland’s day-to-day secretory activity.
This hormone dependence has a downside. Because DHT continuously stimulates the prostate, it commonly drives excessive growth as men age, a condition known as benign prostatic hyperplasia, or BPH.
How the Prostate Changes With Age
Prostate enlargement is one of the most common changes men experience as they get older. Half of all men over 50 show evidence of BPH. By the 60s, the rate climbs to 50% to 70%. Among men over 70, it reaches 80% to 90%. Because the prostate wraps around the urethra, even modest growth can squeeze the urinary channel and cause symptoms: a weak stream, frequent urination (especially at night), difficulty starting or stopping, and a feeling that the bladder hasn’t fully emptied.
These urinary symptoms increase steadily with age. In one large community survey, about 8% of men in their 30s reported lower urinary tract symptoms, compared to 35% of men in their 60s. Prostate enlargement doesn’t affect all men equally, but the trend is consistent enough that most men will notice some change in urinary function over time. The enlargement itself is not cancerous, though prostate cancer is a separate risk that also increases with age and shares some overlapping symptoms.
The reproductive function of the prostate also shifts. As the gland’s tissue composition changes with age, the volume and quality of prostatic fluid can decline. Combined with other age-related changes in testosterone levels and sperm production, this contributes to the gradual decrease in fertility that most men experience in their later decades.